Gravity Field and Structure of the Sorong Zone Eastern

by

Sardjono

Thesis Submitted for the Degree of Ph.D. Department of Geological Sciences University College London

University of London June 1998 ProQuest Number: 10042723

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ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT

Gravity surveys along coastlines of in the Banggai-Sula, Eastern , , Bacan and Obi were carried out as part of the Sorong Fault Zone Project. Results of the Surveys were integrated with gravity data previously acquired by other projects, including on-land gravity data from the Bird Head area Irian Jaya (Dow et al 1986), Seram (Milsom 1977), Bum Island (Oemar and Reminton 1993) and (Silver et al. 1983) as well as marine gravity information within and surrounding the Sorong Fault Zone (Bowin et al. 1980). Gravity expeditions of the Sorong Fault Zone Project also include measurements in Mayu Island and the island group of Talaud, situated further north in the Central Molucca region. A total of one hundred and forty two gravity data were acquired in the region of Banggai-Sula islands, forty seven in eastern part of Central Sulawesi, about four hundred in Halmahera, Bacan and Obi, and seventy nine in Mayu and Talaud. Surveys in the eastern part of Central Sulawesi were carried out for the purpose of tieing the older gravity data obtained from Silver et al. (1983) and the more recent data of the Sorong Fault Zone Project. About one thousand thirty hundred and thirty gravity data were acquired as part of the Irian Jaya Geological Mapping Project (IJGMP) in the period of 1978-1983, a project commissioned by the Indonesian Geological Research and Development Centre (GRDC) and the Australian Bureau of Mineral Resources (BMR). The remoteness of the survey areas of the Sorong Fault Zone Project necessitated a careful planning for travel arrangements and provision of logistics.

A wide range of magnitude of gravity field was observed in the Sorong Fault Zone, extending from values below -250 mGal recorded in the southern part of the to values in excess of +320 mGal measured near to sea level in the coastal areas south of Mangole and north of Sulabesi, the two islands of the Sula Group. Steep gradients of free-air gravity were observed in south of Mangole (about 13 mGal/km) and west of Obi (about 15 mGal/km) but elsewhere were gentler. Analyses of gravity data along the Sorong Fault Zone in the region of Bar ggai-Sula Islan ds controlled in part by geological, reflection seismic and sidescan sonar data, have produced four models which suggest that the crustal structures beneath the zone consist predominantly of attenuated continental fragments, juxtaposed to thick layer of tectonic mélange and anomalous oceanic crusts. The continental fragments appear to be severely attenuated and limited in extent in the east but thicker and wider towards the west. The tectonic mélange is underlain by deep seated oceanic crust in the Molucca Sea region. The anomalously thin North crust appears to underlie a very thin layer of sediments and to have suffered some degree of arching. The deep seated oceanic crust and the thick layer of tectonic mélange are interpreted as the resuh of the shiMng of the lithospheric plate of the Molucca Sea. The descent of this :ç,hte :T.iy have producced bending forces which may have initiated flexure which propagates through the surrounding region. Depending on the rigidity of the crustal slab, arching and fracturing may have occurred in the crustal rocks. The arching of the oceanic crust of the North Banda Sea may have been one result of this process. The continental fragments of the Banggai-Sula region appear to dip northwards and this may, in addition to the effect of tectonics along the Sorong Fault Zone, also be interpreted as the response of the continental fragments to the sinking of the lithospheric plate of the Molucca Sea. In the Obi region, the gravity data suggest that most of the island is underlain by peridotitic and basaltic rocks. Continental crust appears to form the basement in the south and extend offshore south of the island and juxtaposed to oceanic rock. The ultramafrc and basic rocks appear to be emplaced on Obi by a high angle reverse fault which separates the continental block in the south from the oceanic material in the north. The exposed basaltic rocks could be a remnant of the oceanic crust of the Plate.

Ill ACKNOWLEDGMENT

Financial support for this project was provided by the University of London Consortium for Geological Research in Southeast . Equipment and personnel for gravity expeditions were provided by the Geological Research and Development Centre (GRDC), Bandung, Indonesia.

My appreciation is due to Professor Robert Hall for bringing me to join the research team of the Sorong Fault Zone Project. My thanks are also due to Dr. Rah Sukamto the former director of GRDC and his successor. Dr. Irwan Bahar, who have granted me a temporary leave from the service. I truly thank Diane Cameron, the Administrator of the Southeast Asia Research Group, for helping me with all aspects of formalities. My thanks are also due to all academic and administrative staff as well as all members of the Birkbeck College and University College London Research School of Geological and Geophysical Sciences who have provided personal and professional assistance towards the completion of this study.

Finally, my sincere gratitude is due to Dr. John Milsom for initiating and supervising this project. Dr. Milsom has always provided valuable assistance and practical advice in all aspects of this study and has spent a considerable amount of time in reading, criticising and subsequently making corrections to this thesis.

IV CONTENTS

ABSTRACT ii ACKNOWLEDGMENT iv CONTENTS V LIST OF FIGURES viii LIST OF TABLES x

CONTENTS

Chapter 1 INTRODUCTION 1 1.1 Background 1 1.2 Gravity Expedition in the Sorong Fault Zone 3 1.3 Organisation of the Thesis 10

Chapter 2 THE PRINCIPAL FACTS 15 2.1 Observed Gravity 15 2.2 Longitude and Latitude 18 2.3 Height 19 2.4 Accuracy of the Gravity Map 22

Chapter 3 GRAVITY REDUCTION AND INTERPRETATION TECHNIQUES 27 3.1 The Reduction of Gravity Data 27 3.1.1 The latitude correction 32 3.1.2 The free-air correction 3 3 3.1.3 The Bouguer correction 3 6 3.1.4 Terrain correction 39 3.1.5 Isostatic effects 42 3.1.6 Geological correction 43 3.1.7 Correction for shipbome observations 44 3.2 Interpretation Techniques 45

Chapter 4 TERRANE GEOLOGY OF THE SORONG FAULT ZONE 51 4.1 Introduction 51 4.2 Fault Strands of the Sorong Fault Zone 53 4.2.1 Sorong Fault 53 4.2.2 Koor Fault 54 4.2.3 Molucca-Sorong Fault 55 4.2.4 North Misool-Sorong Fault 56 4.2.5 Bum Fracture 56 4.2.6 Seram Trough 57 4.2.7 North Sula-Sorong Fault 57 4.2.8 South Sula-Sorong Fault 58 4.3 Oceanic Terranes ‘jg 4.3.1 Molucca Sea Collision Zone 59 4.3.2 North Banda Sea 60 4.4 Arc Terrane of the 62 4.4.1 West Halmahera-Tamrau Terrane 62 4.4.2 East Halmahera- Terrane 63 4.4.3 Arfak Terrane 64 4.5 Continental Terranes 65 4.5.1 Banggai-Sula Platform 65 4.5.2 -Seram Microcontinent 67 4.5.3 Misool Terrane 68 4.5.4 Kemum Terrane 68 4.5.5 Netoni Terrane 69 4.6 Amalgamated Terrane 69 4.6.1 East Sulawesi Terrane 70 4.6.2 Obi Terrane 70 4.6.3 Bacan Terrane 71

Chapter 5 SIDESCAN SONAR, SEISMIC IMAGES AND SEISMICITY 86 5.1 Sidescan Sonar 86 5.1.1 Eastern arm GLORIA coverage 88 5.1.2 Central region GLORIA coverage 91 5.1.3 Northern Arm GLORIA coverage 92 5.1.4 Southwestern arm GLORIA coverage 93 5.1.5 Southeastern arm GLORIA coverage 94 5.2 Seismic Images 95 5.2.1 Seismic images Segment 1 96 5.2.2 Seismic images Segment 2 97 5.2.3 Seismic images Segment 3 98 5.2.4 Seismic images Segment 4 98 5.2.5 Density analyses based on velocity of seismic wave 98 5.3 Seismicity 99

Chapter 6 GRAVITY FIELD AND STRUCTURE OF THE SORONG FAULT ZONE, EASTERN INDONESIA 114 6.1 Introduction 114 6.2 Provinces of Gravity Anomalies in Sorong Fault Zone 115 6.2.1 Gravity province of Kepala Burung (1) 116 6.2.2 Gravity province of the North (2) 117 6.2.3 Gravity province of the North Banda Basin (3) 119 6.2.4 Gravity province of Southeast Arm Sulawesi (4) 121 6.2.5 Gravity province of East Arm Sulawesi 122 6.2.6 Gravity province of the South Molucca Sea 123 6.2.7 Gravity province of Halmahera (7) 126

VI 6.2.8 Gravity province of Obi ( 8 ) 128 6.2.9 Gravity province of the Sula Group (9) 128 6.2.10 Gravity province of the Banggai Islands (10) 131 6.3 Structure of the Sorong Fault Zone 132 6.3.1 Crustal structure of Western Mangole Island 134 6.3.2 Crustal structure of the shelf region West Taliabu 138 6.3.3 Crustal structure of the Banggai Islands 141 6.3.4 Crustal structure of the Obi region 146

Chapter 7 CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDIES 189 REFERENCES 192 APPENDICES Appendix A Gravity anomalies in Talaud Islands, Central Molucca Sea 200 Appendix B Gravity data reduction spreadsheets 204 B.l. Example of spreadsheet for gravity data reduction 204 B.2. Spreadsheet templates for gravity data reduction 205 Appendix C Gravity Data Sorong Fault Zone Project 1978-1993 222 C.l Gravity Expedition 1987 222 C.2 Gravity Expedition 1989 226 C.3 Gravity Expedition 1990 230 C.4 Gravity Expedition 1992 234 C.5 Gravity Expedition 1993 239 Appendix D List of principal base stations of the Indonesian Regional Gravity Network and sketches of base stations established during the gravity expedition of the Sorong Fault Zone Project 241 Appendix E Barometric Levelling 248 Appendix F Information on density rocks in Sorong Fault Zone and Kai Islands Region 250

VII LIST OF FIGURES

Chapter 1 Fig. 1.1 Tectonic setting of Eastern Indonesia and the surrounding region 11 Fig. 1.2 Tectonic elements within and surrounding the Sorong Fault Zone 12 Fig. 1.3 National Gravity Base Station Network of Indonesia 13 Fig. 1.4 Areal coverage of gravity expeditions of the Sorong Fault Zone Project 14

Chapter 2 Fig. 2.1 G240 gravity meter drift record, expedition 1992 25 Fig. 2.2 G826 gravity meter drift record, expedition 1993 25 Fig. 2.3 Typical diurnal variation of barometric pressure 26

Chapter 3 Fig. 3.1 Relationship between geoid, ellipsoid and topography 48 Fig. 3.2 Various elements in gravity data reduction 48 Fig. 3.3 Gravitational effect of a cylindrical ring element 49 Fig. 3.4 Gravitational effect of a right circular cone 49 Fig. 3.5 Mass inhomogeneity above datum and the Extended Bouguer Gravity 50

Chapter 4 Fig. 4.1 Terrane tectonic in the Sorong Fault Zone 72 Fig. 4.2 A tectonic model of Eastern Indonesian Region 73 Fig. 4.3 Bathymetry of the Sorong Fault Zone and the surrounding region 74 Fig. 4.4 Interpreted seismic profiles and strands of the Sorong Fault 75 Fig. 4.5 Interpreted seismic profiles north of Sula Islands region 76 Fig. 4.6 Terranes of Kepala Burung area, Irian Jaya 77 Fig. 4.7 Earthquake foci beneath the Molucca Sea Collision Zone 78 Fig. 4.8 A gravity model of the Molucca Sea Collision Zone 79 Fig. 4.9 Simplified geological map of Halmahera 80 Fig. 4.10 Simplified geological map of Waigeo 81 Fig. 4.11 Simplified geological map of Banggai-Sula region 82 Fig. 4.12 Simplified geological map of Buru-Seram Microcontinent 83 Fig. 4.13 Simplified geological map of Obi 84 Fig. 4.14 Simplified geological map of Bacan 85

Chapter 5 Fig. 5.1 GLORIA sidescan imagery of and parts of Sorong Fault Zone 104 Fig. 5.2 Line drawing interpretation of sidescan sonar imagery 105 Fig. 5.3 Approximate location of seismic line QS-1 106 Fig. 5.4 Segment 1 seismic line QS-1 107 Fig. 5.5 Seismic images and characteristics of drowning carbonate platform 108 Fig. 5.6 Segment 2 seismic line QS-1 109 Fig. 5.7 Segment 3 seismic line QS-1 110 Fig. 5.8 Segment 4 seismic line QS-1 111

Vlll Fig. 5.9 Seismicity of the Sorong Fault Zone and the surrounding region 112 Fig. 5.10 Lithospheric sections and seismicity in the Sorong Fault Zone 113

Chapter 6 Fig. 6.1 Gravity contour map of the Sorong Fault Zone 151 Fig. 6.2 Provinces of gravity anomalies in the Sorong Fault Zone 152 Fig. 6.3 Residual gravity anomalies of Sulabesi (minimum curvature trend) 153 Fig. 6.4 Residual gravity anomalies of Sulabesi (maximum curvature trend) 154 Fig. 6.5 Scenario of dispersion of Sulabesi and Mangole 155 Fig. 6.6 Standard crustal sections 156 Fig. 6.7 Lines of gravity profiles analysed for crustal models 157 Fig. 6.8 Location of Western Mangole gravity profile 158 Fig. 6.9a and 6.9b Preliminary crustal structure of Western Mangole region 159 Fig. 6.9c and 6.9d Dips the Moho and adds thick mélange to match observation 160 Fig. 6.9e and 6.9f Introduce oceanic crusts and sediments improves the match 161 Fig. 6.9g and 6.9h Typical flower structure and depression of the Moho 162 Fig. 6.9i and 6.9j Possible structures of Western Mangole crust 163 Fig. 6.10 Gravitational effects of crustal layers of Western Mangole 164 Fig. 6.11 Location of the gravity profile of the shelf region West Taliabu 165 Fig. 6.12a and 6.12b Gravitational effects of seawater and Moho at about 20 km 166 Fig. 6.12c and 6.12d Thins oceanic crust of North Banda Sea improves the match 167 Fig. 6.12e and 6.12f Introduce mélange and arc-volcanics to improve the match 168 Fig. 6.12g and 6.12h Carbonate platform and reef build-up to improve the match 169 Fig. 6.13 Gravitational effects of crustal layers of the shelf region West Taliabu 170 Fig. 6.14 Location of the gravity profile of the Banggai Islands region 171 Fig. 6.15a and 6.15b Effects of the water layer and the Moho at about 20 km 172 Fig. 6.15c and 6.15d Gravitational effects of mélange and oceanic crust 173 Fig. 6.15e and 6.15f Adjustments of Moho and mélange to improve the match 174 Fig. 6.15 g and 6.15h Alternative Moho and introduction of sediments 175 Fig. 6.15i and 6.15j Thick oceanic crust in Tomori Basin to match observation 176 Fig. 6.15k and 6.151 Tomori Basin is underlain by continental fragment 177 Fig. 6.15m and 6.15n Alternative crustal structures of Banggai Islands region 178 Fig. 6.16 The 2-D and 2 V2-D responses of crustal model of Banggai Islands 179 Fig. 6.17 Location of gravity profile across Obi 180 Fig. 6.18a and 6.18b Effects of seawater and the Moho at about 20 km 181 Fig. 6.18c and 6.18d Gravilati ji^a; effects of lower Moho and ultramafrc block 182 Fig. 6.18e and 6.18f Gravitational effects of a block of basic rocks 183 Fig. 6.18g and 6.18h Effects of oceanic crust and arc-volcanics 184 Fig. 6.18i and 6.18j Gravitational fleets of sediments and dipping basalt block 185 Fig. 6.18k and 6.181 Effects of altering the geometry of crustal block in the south 186 Fig. 6.18m, 6.18n and 6.180 Effects of oceanic crust, sediments and mélange 187 Fig. 6.19 The 2-D and 2Î4-D responses of crustal model of Obi region 188

IX Appendix D Fig. D.l Gravity base station Lining Harbour, Talaud Islands 243 Fig. D.2 Gravity base station Luwuk Hotel Melati 244 Fig. D.3 Gravity base station Luwuk Bubung Airport 245 Fig. D.4 Gravity base station Banggai, Banggai Island 246 Fig. D.5 Gravity base station Kolonodale Hotel Lestari 247

LIST OF TABLES

Chapter 3 Table 3.1 Corrections in the reduction the gravity data of the Sorong Fault Zone Project 32 Table 3.2 Relationship between R/H and g/gp, 37 Table 3.3 Relationship between (j> and g/gp 38

Appendix D Table D. 1 List of principal gravity base stations in Indonesia 241

Appendix F Table F. 1 Density values derived from velocity of seismic waves 250 Table F.2 Density values of rock samples from Sula Islands region 258 Table F.3 Density values of rock samples from Kai Islands region 258 Chapter 1 INTRODUCTION

1.1 Background

The Sorong Fault Zone (Fig. 1.1) is defined for the purpose of this thesis as the region extending from Kepala Burung (Irian Jaya) in the east to the East Arm of Sulawesi in the west (Hall et al. 1987). It is a major left-lateral fault system which separates from the Philippine Sea Plate and which juxtaposes Mesozoic- Tertiary continental rocks with arc volcanic and ophiolitic rocks. The continental crust was derived from the Australian margin, whereas the arc and ophiolitic rocks are believed to have originated from the Philippine Sea Plate (Hall et al. 1987).

The Sorong Fault Zone is situated in Eastern Indonesia which occupies a zone of convergence between three of the ’s major lithospheric plates, the Indo-Australian, the Eurasian and the Philippine Sea Plate. This convergence zone (stippled area in Fig. 1.1) extends northwards to include the northern Molucca Sea region, southwards covering Timor and eastwards encompassing the northern part of and offshore Irian (). It is one of the most complex and active tectonic region on the Earth and includes a number of small basins, such as the Molucca Sea, which cannot be assigned to any of these three main plates.

The interaction between the three major lithospheric plates is in the form of oblique convergence which has developed the Sorong Fault Zone as a shear zone. The present tectonic scheme resulted as the Australian moved northwards relative to the Eurasian and the Philippine Sea plates during the Tertiary. Since the Neogene, the Australian continental block has moved past the southeast margin of the Eurasian Plate and has collided with the Philippine Sea Plate. Palaeomagnetic studies (Hall et al. 1987) have indicated that the Australian Plate moves NNE at a rate of about 75 km/Ma and the Philippine Sea Plate moves WNW at a rate of about 105 km/Ma, whereas the Eurasian Plate has only moved very small distance and can, to a first approximation, be regarded as a stationary frame of reference. This interaction results in oblique convergence between the Indo-Australian Plate and the Philippine Sea Plate oriented WSW-ENE, at a rate of about 130 km/Ma (see inset Fig. 1.1).

In the Kepala Burung area, the Sorong Fault system (Fig. 1.2) is a clearly defined zone of left-lateral faulting with an average width of about 10 km (Tjia 1973). To the west of the Sorong area, the fault splits to form the Molucca-Sorong Fault, the South Sula-Sorong Fault, the North Sula-Sorong Fault (Hamilton 1979) and the Bum Fracture (Tjokrosapoetro and Budhitrisna 1982). Stmctural lineaments which are generally oriented E-W may be traced on bathymetric map of the region (e.g. Mammerickx et al. 1976) and identified on seismic section (e.g. Letouzey et al. 1983) and side-scan sonar (GLORIA) images traversing the fault zone obtained during the 1988 RRS Charles Darwin cmise (Masson et al. 1988). At the western end, the fault zone terminates in the fold and thmst belt of eastern Sulawesi (Hall et al. 1987).

The Sorong Fault Zone Project was established in order to investigate the processes by which terranes formed and were subsequently transported and amalgamated in orogenic belts (Hall et al. 1987). The investigation used methods of terrane analysis which involved palaeomagnetic, stratigraphie, stmctural and sedimentary provenance studies as well as the geophysical studies which are the subject of this thesis. Results from palaeomagnetic, stratigraphie, stmctural and sedimentary provenance studies provide information on surface, allowing terrane boundaries to be delineated as well as the history of geology and tectonic to be reconstmcted. Results from the geophysical studies on the other hand provides, in addition to the terrane distribution, control in the third dimension i.e. depth or thickness of terrane blocks.

The geophysical work done in the course of the Sorong Fault Zone Project comprised acquisition, processing and interpretation of gravity data. Fieldwork on the gravity surveys consisted of measurements of gravity fields in the coastal areas of the islands within and surrounding the fault zone. The data processing included reduction of raw data to obtain the Bouguer gravity values, integration of the coastal gravity data with marine free-air data and other information obtained from previous studies (Milsom 1977, Bowin et al. 1980, Silver et al. 1983 and Dow et al. 1986) and presentation of the data in the form of gravity contour maps. The interpretation was based on the testing of models of crustal structure against the gravity observations using the GM-SYS™

gravity modeling program running under MS-DOS ®. As well as utilising gravity data to constrain the crustal configuration, other controls such as bathymetry, sedimentary isopach, reflection seismic and sidescan sonar images were used whenever possible and available.

1.2 Gravity Expedition in the Sorong Fault Zone

Gravity work in Indonesian waters in general and in the Sorong Fault Zone in particular dates back to an expedition using pendulum apparatus on board of a submarine (Vening Meinesz 1948) which culminated in the publication of the first isostatic gravity map of the Indonesian Archipelago. Because of the wide separation between the pendulum stations, these measurements could only resolve major crustal features, leaving smaller ones undetected. More recent marine gravity expeditions which also covered the Sorong Fault Zone were the results of joint efforts between the Geological Survey of Indonesia (GSI) and the United States Geological Survey (USGS), and these culminated in the publications of geophysical maps and geoscientific papers (Silver and Moore 1978, Bowin et al. 1980, Moore and Silver 1983, Silver et al. 1983) which in turn gave a strong stimulus to further investigations. Further work was carried out by Indonesian government organisations and private oil companies, and in joint co-operation project between Indonesian and foreign scientific institutions. Results from these expeditions, which included a coastal survey of Seram and Ambon islands just to the south of the project area (Milsom 1977), were incorporated into the present study to complement the coastal measurements made during the course of the Sorong Fault Zone Project.

Systematic gravity mapping in Indonesia started in the 1960’s and was pioneered by the Geophysical Section of the GSI with Mohamad Untung as the head of the section. The author joined the section in 1974 whilst finishing a university degree at the Institute of Technology Bandung. At that time access difficulties restricted gravity survey operations to the mapping of Java and islands or provinces close to Java.

A regional gravity base station network for the whole of Indonesia was established in the early 1970’s (Adkins et al. 1978). Measurements were made using LaCoste- Romberg geodetic gravity meters at major airports throughout the country relying on commercial airliners as the primary transport, allowing loops which contained one or more stations to be closed in one day or less, giving sufficient control on the drift of the instruments. This national gravity base station network (Fig. 1.3) was linked to the international absolute stations at Singapore Paya Lebar and Sydney Kingsford Smith airports and was referenced to values of absolute gravity based on the International Gravity Standard Network 1971 (IGSN 1971). The base station network provided calibration facilities for subsequent gravity measurements throughout the country.

Gravity mapping on remote islands such as Irian Jaya was initiated in 1978 as a joint co-operation project between the Indonesian Geological Research and Development Centre (GRDC) and the Australian Bureau of Mineral Resources (BMR), and was carried out under the auspices of the Irian Jaya Geological Mapping Project (IJGMP) which lasted from 1978 to 1986. This project concluded with the publication of the geological map of Irian Jaya on which gravity contours were superimposed (Dow et al 1986). The author was a member of the gravity field party of the IJGMP between 1980 and 1981, when the field acquisition was based in Manokwari, situated not far from the intersection between the E-W oriented Sorong Fault and the NNW-SSE oriented Ransiki Fault (Fig. 1.2). The author was also involved in fieldwork near Wasior and Nabire which are situated a short distance to the southeast of the present study area.

The IJGMP was implemented utilising helicopters as the primary method for gaining access to gravity stations, allowing fast and efficient coverage of the region. Other methods of transport were river work boats and larger vessels which were used in swampy and remote areas which prohibited the use of helicopters. A number of auxiliary base stations were established during this project which were directly linked to the nation-wide network (Marzuki and Sukardi, pers. comm. 1992). Gravity measurements were made at about 10 km intervals and the map was drawn at 5 mGal contour intervals. Some data from earlier surveys in Irian Jaya (Visser and Hermes 1962) were reprocessed and included in the IJGMP map. This gravity map was incorporated into the present study and defines the gravity field in the eastern part of the Sorong Fault Zone.

There were five distinct gravity surveys during the course of the Sorong Fault Zone Project, which lasted from 1987 to 1993 (Fig. 1.4). The first three sessions of fieldwork were carried out in 1987, 1989 and 1990 with the assistance of GRDC personnel including Daniel Lelitoly, Didi Pandu Tasno, Agus Haryono, Saultan Panjaitan and Tatang Padmawidjaja. The present author completed the work in two surveys, in 1992 and 1993.

The primary means for gaining access to the coastal gravity stations was by boat but when sea was to rough and road or tracks existed, approaches were made from land using either motorized vehicle or traversed on foot. A diesel-powered boat with a capacity of about 30 to 40 tonnes and a light (2 m wide by 5 m long) outboard-powered wooden speed boat were a perfect combination to support the expeditions, especially for long traverses which lasted up to 30 days in isolated areas where fuel and other essentials were scarce. Fuel, lubricants, spare parts, foods and other necessities had to be purchased from the larger towns but fresh water was obtainable at places en-route. Apart from functioning as the primary transporter, the larger boat was used as field office, workshop and sleeping quarter, capable of accommodating 5 survey personnel in some degree of comfort. This kind of boat is typically manned by 8 to 10 persons. The smaller speed boat with a 15 HP outboard engine could produce 8 to 12 gravity stations daily at 3 to 4 km intervals, depending on the state of the sea and the landing ground. When a motor boat was not available and a sampan was used instead, productivity was reduced by about 40%, so that only 5 to 7 stations could be occupied per day (A sampan is a variety of canoe about 0.6 m wide by 3 m long, made from a single log timbre. It is usually used by local people for commuting from one village to another or from villages to plantation areas where they usually work. Alternatively, it may simply be used for small scale fishing at short distance from villages). On shorter traverses (10 days or less) a wooden boat with a capacity of about 3 to 5 tonnes, powered either by a small diesel engine or an outboard motor, or combination of both, could produce 7 to 9 coastal gravity stations per day at interval 3 to 4 km. This mode of operation limited the number of survey personnel, allowing only one geophysicist, one geologist and three crew members.

On land, use was made of motorized vehicles whenever possible, but where roads did not exist, traverses had to be made on foot following narrow tracks along or adjacent to the coast. Tracks which connect villages are usually sufficiently wide for this work but in any other cases, cutting was necessary. Depending on the quality of the roads, access using motorized vehicles produced 8 to 12 gravity stations per day and traverses on foot produced 5 to 7 gravity stations daily, at intervals between 3 and 4 km.

The first gravity expedition of the Sorong Fault Zone was carried out within the period of July to September 1987. GRDC geophysicists Daniel Lelitoly and Didi Pandu Tasno made gravity measurements along the coasts of Temate, Bacan and South Halmahera (Fig. 1.4). A total of 164 gravity stations were occupied. Access was by a 30 tonnes transporter and a light wooden speed boat. Links to the national gravity network (Adkins et al. 1978) were made by tieing a new base station on Temate to the national base station at Pattimura airport, Laha, on the island of Ambon. Links were also made to the UGMP survey by reoccupying a base station at Jefinan Island airport in Sorong. Measurements were also made on the islands of Gebe, Gag and Waigeo whilst sailing from South Halmahera to Sorong.

The second gravity expedition was conducted in the period from October to November 1989. Gravity measurements were made along the coastlines of the islands of Bacan, Obi, Sulabesi and Mangole (Fig. 1.4) by Agus Haryono and Saultan Panjaitan (GRDC), occupying 167 coastal stations. Access to coastal gravity stations was by a 30 tonnes transporter combined with a light wooden speed boat. Measurements were again linked to the national gravity network at Pattimura airport Laha, on . In­ land gravity surveys on Obi has also been done by PT Gondwana for PERTAMINA (Indonesian State Oil Company) and several data points from these surveys (Agustiyanto, pers. comm. 1994) were incorporated in the present study to provide some control on contouring the gravity field on Obi.

The third gravity expedition was carried out within the period between October and November 1990. Gravity measurements were made by Tatang Padmawidjaja (GRDC) along the coastlines of North Halmahera and (Fig. 1.4), producing 169 new gravity stations in this area. A 30 tonnes transporter and a light wooden speed boat were again used for gaining access to the coastal gravity stations. Links to the national gravity network were made by tieing these measurements to the base station at Pattimura airport Laha, on Ambon Island via the auxiliary base station on Temate. Results of the first, second and third gravity expeditions of the Sorong Fault Zone Project have been documented by Milsom et a/. (1991) and have been incorporated into the present study.

The fourth gravity expedition was in the period from October to November 1992. Gravity measurements were carried out by the author covering the coastlines of Mayu and Talaud Islands in the central Molucca Sea region (Fig. 1.4). Measurements were also made on the Banggai Islands and the islands of the Sula Group which are situated between the South Molucca Sea and the North Banda Sea (Fig. 1.4).

Surveys in Mayu and Talaud used a small wooden speed boat and a 30 tonnes transporter which were hired from Temate. Mayu is both small and isolated in the central Molucca Sea region (inset A Fig. 1.4). Gravity measurements were made at 7 stations with an interval between 3 to 4 km along the coast around the island. The Talaud Islands consist of Karakelang, Salebabu and Kabaruan (inset B Fig. 1.4). A total of 72 gravity stations with an interval ranging from 3 to 4 km were occupied along the coast of these islands. Access was mainly by boat but approaches from land were made when surveying west coast of Karakelang. These were done because of the rough condition of the sea which prevented the use of boat to make safe landing. A van was hired from Rainis for surveying the southem half of the west coast of Karakelang from Beo to a station near Melong. Surveys on the northem half of the west coast of Karakelang was done on foot, traversing from the northem tip of the island to Beo, on the completion of survey on the east coast. A good road only extended a few kilometres north of Beo, leaving the rest of the northem half of the west coast inaccessible to motorized vehicles. All measurements in Mayu and Talaud were linked to national gravity network through the base station at Hasanuddin airport, Ujung Pandang, Sulawesi.

The Banggai Islands consist of Peleng, Labobo and Bangkurung (inset C Fig. 1.4). A total of 75 gravity stations at an average interval of about 3 km were occupied along the coastlines of these islands. In this survey, a 5 tonnes wooden boat powered by a small diesel engine was used for gaining access to the coastal gravity stations. The boat which was also fitted with a 15 HP outboard engine was locally hired in Banggai, the principal administrative town of the Banggai Islands. The outboard engine was used to provide additional speed when required. As well as using a boat, access was made from land using a hired tmck to carry out measurements along the east coast of the island of Banggai. This was again due to high surf which prevented safe approach using a boat.

Surveys on the islands of the Sula Group was carried out using a 10 tonnes transporter and a sampan for accessing stations on the coast. This diesel-powered boat was hired from the town of Banggai, as regular ferry services between Banggai and Taliabu were unavailable at the time of the survey. Merchant boats occasionally sail from Southeast Sulawesi to Taliabu and other islands in the Sula Group via Banggai but there is no consistent timetable for these irregular voyages.

The Sula Group consists of Taliabu, Mangole and Sulabesi (inset D Fig. 1.4) and lies between the South Molucca Sea and the North Banda Sea. Sulabesi and Mangole had both been covered during the 1989 survey. In 1992, a total of 17 gravity stations were established on the south coast of Taliabu and 4 on south coast of Mangole. The purpose of resurveying a part of Mangole was to either confirm or eliminate a single point gravity high obtained in the 1989 survey by Agus Haryono (GRDC). The measurements on Mangole in 1992 confirmed the gravity high encountered in the previous survey. An equipment failure prevented measurements being made along the north coast; the electric generator which had been hired from Luwuk (East Arm of Sulawesi) was broken and could not be repaired. Moreover, at that time (end of November 1992), the monsoon was already creating high surf which prevented a safe access to stations on the north coast of Taliabu. Roads or logging tracks probably exist along the north coast but period for boat hire had ended and decision was made to end the expedition.

All measurements in the Banggai-Sula region were linked to the national gravity network through the base station at Hasanuddin airport, Ujung Pandang, on Sulawesi. Results and operational aspects of the 1992 expedition are documented in Sorong Fault Zone Project Report No. 121 (Sardjono 1992).

The fifth gravity expedition of the Sorong Fault Zone Project was carried out in the period between June and July 1993. Measurements were made by the author along a traverse from Kolonodale and Rata in the north to Labota in the south. A total of 47 gravity stations were established at an average interval of approximately 4 km. The main aim of this small piece of fieldwork was to establish a link between the Sorong Fault Zone gravity survey and the work carried out by the University of California in Central Sulawesi (Silver et al 1983).

An outboard-powered wooden boat with a capacity of about 3 tonnes was used for gaining access to gravity stations around the bay near Kolonodale, but because of the rough condition of the sea where the coast faces the open sea of the , use was made on a motor bike for surveying the coastline from Kolonodale to Labota village where road terminates. Construction of a road through to Kendari was in progress at the time of the survey.

Links to the national gravity network were made by tieing all measurements to the gravity base station at Hasanuddin airport, Ujung Pandang, on Sulawesi. A link was also made in 1993 between Luwuk and Banggai to control the high drift observed during the 1992 survey of the Banggai Islands. 1.3 Organisation of the Thesis

The thesis contains seven chapters, a bibliographic section and appendices. This chapter has reviewed the tectonic background to the region surrounding the study area and discussed gravity work in the study area. Chapter 2 describes data acquisition and accuracies on the gravity surveys carried out by the author and also discussed aspects of previous gravity investigations jfrom which results have been incorporated into the present study. Chapter 3 describes the reduction and interpretation techniques applied to the gravity data. Chapter 4 discussed the geology of the study area in terms of the distribution of terranes.

The images produced by sidescan sonar (GLORIA) and seismic reflection surveys in the Sorong Fault Zone are analysed in Chapter 5 in which the seismicity of the area is also reviewed. Chapter 6 discusses the gravity field of the Sorong Fault Zone in terms of the identified anomalies in areas within the zone and presents analyses of the fault zone in terms of crustal gravity models. Chapter 7 completes the thesis with conclusions and recommendations for future work.

Four appendices containing the pertinent information in regard to this study accompany this thesis. Appendix A discusses survey results obtained on the Talaud Islands, north of the Sorong Fault Zone in 1992, which are marginally related to the present study. Appendix B contains an example of the spreadsheet for the reduction of gravity data using Quattro Pro™ program. Appendix C catalogues the gravity data acquired during the course of the Sorong Fault Zone Project. Appendix D contains descriptions and principal facts for base stations used in the present study. The theory and practice of barometric leveling are briefly reviewed in Appendix E. Appendix F contains information on the density of various crustal rocks in parts of the Sorong Fault Zone and the Kai Islands region which is situated to the south of the eastern portion of the fault zone.

10 Kilometres

Active convergent zone or intraplate thrusting PHILIPPINE Spreading centre SOUTH Spreading centre and transform fault EURASIAN Zone of normal faulting PHILIPPINE [archipelago Zone of strike slip faulting ANDAMAN CHINA %

PHILIPPINE PLATE SEA II AYU TROUGH MOLUCCA II PLATE % II .SORONG FAULT ZONE NEW GUINEA KALIMANTAN [^KEPALA TRENCH URUNG o SULAWESI RIAN BISMARCK NOR JAYA INDIAN BANDAr / \...... ^ IRIAN SEA yB A N D A i l (NEW GUINEA) SE A , / ^ t ^ SOLOMON JAVA ______^ TIMOR NEW GUINEA

CORAL SEA

Schem atic of convergence vectofs OCEAN AUSTRALIA 25Km

I105°E 112CPE

F ig u re 1.1 Tectonic setting of Eastern Indonesia and the surrounding region, showing the Sorong Fault Zone study area. The stippled area indicates the zone of interaction between the three major lithospheric plates; Indo-Australian, Eurasian and Philippine Sea Plate (After Rangin 1991, Hall et a l 1 9 9 2 ). ^ Active convergent zone or intraplate thrusting Talaud Zone of strike slip faulting Islands

Zone of normal faulting Kilometres 200

Morot» Sangihe Islands PHILIPPINE

o r / Mofotal SEA

Manado HALMAHERA

NORTH N ew Guinea -ARM SORONG FAULT ZONE Trench GebeN^ o Koof F«uH sw-ARM G ag o Waigeo M tnokwAri TOMINI MOLUCCA Batant SEA X BACAN to BANGGAI-SULA Raja Ampat Is. Sorong Fault MICRO-CONTINENT r

North Sul«*Sororra Kepala % Ytpan Fault Fault Y apen Misool Burung

ULFOF Sulabesi .sorong K Blntuni B«y

NORTH BANDA ^ SERAM SULAWESI SEA ^ ------\ A Tolo IRIAN JA YA Thrust \

SOUTHEAST SOUTHWEST GULF ARM OF o4»n«e» BONE Kai Islands Pandang BANDA SEA Tukanfl Bm i Islands Itlamls

Selayar ARAFURA SEA SOUTH BANDA SEA iiee-E 13/re I l3fE ____ I raffc Figure 1.2 The Eastern Indonesian Region, showing tectonic elements in and surrounding the Sorong Fault Zone. (Sources Hamilton 1979, L etouzey etal. 1983, Hall etal. 1990, Rehault etal. 1991, Hall etaL 1992, Milsom eta l 1992). ANDAMAN ^ . PHILIPPINES PHILIPPINE O ’ V, 11 SEA

SOUTH SABAH . ^ CHINA

CELEBES SEA MOLUCCA

M m do 28 PAC F C O C E A N SINGAPORE

KALIMANTAN SULAWESI

PAPUA IRIAN JAYA NEW GUINEA

,135-E UO'E w Jakarta B , BANDA SEA S'eanduST "— FLORES SEA - NDIAN 20 21 ^ y Æ -cS» 9 _ SEA AUSTRALIA SUMBA 25 0 CE 4 /V TIMOR Sydney Kilometres SEA

120'E . .140 100'E 105'E 110'E , 120'E______, 125' 130'E Figure 1.3 Indonesia National Gravity Base Network (Adkins et al. 1976). Links to the International absolute values were made by connecting the network to absolute stations through Paya Lebar airport Singapore and Kingsford Smith airport Sydney Australia. Absolute stations are located at the University in Singapore and at Sydney University Australia. Appendix D lists the principal facts of the base stations, including the absolute stations and auxiliary base stations established during the gravity expeditions of the Sorong Fault Zone Project. TALAUD MAYU ISLAND • Gravity Station SOUTH ISLANDS MOLUCCA SEA 6 Km 20 MANGOLE TALIABU KARAKELANG' Falabisaya Bobong 1992(4) B«, • Qravity Station MOLUCCA Sanana ■ Principal TowrWflago SEA SEE INSET B NORTH 10 Km BANDA • Gravity Station SULA SEA SULABESI GROUP MOLUCCA 50 Km SALEBABU CELEBES

SEA 1990(3) SEA NW SEE HALMAHERA INSET A •ARM PHILIPPINE Mayu 0

NORTH ARM 1992(4) SE-ARM MAKASAR TIfore' / 1 9 87(1)^ SEA Waigeo GULF G ebe, Kasiruta Manokwari OF Poh Head TOMINI SOUTH SEE Balanta o—^ Palu MOLUCCA SEA BACAI Sorong KEPALA INSET C Oo \ Biak EAST A BURUNG ] 1992(4) SULA GROUP KoKau Salawati STRAIT OBI BANGGAI Falabisaya Ya^ii ^ a Rata ^ Æ ot)ong ISLANDS V i 993(5) Kolonodale Bintunl Bay SULA WES! 1992(4) SE R A M SEA SEE \ Onin INSET E SEE INSET D Peninsula Labota SERAM NORTH Nabire BANDA SEA 1 BANGGAI Rata IR IA N JAYA SS ISLANDS

SOUTHWEST PELENG ARM ARAFURA GULF Kolonodale) Bay BANDA SEA OF GULF Ujung Pandang BONE OF TOLO SEA Dobto

Aru SOUTH Islands BANDA SEA Kilometres 200 FLORES SEA

Figure 1.4 Geography of the Sorong Fault Zone, showing Mayu Island, the island group of Talaud, the Banggai Islands, the Sula Group and the east coast of Central Sulawesi survey areas. Blocks indicate dates of gravity surveys and approximate areas covered. Insets show more details of the locations of those surveys which were carried out by the author. Chapter 2 THE PRINCIPAL FACTS

2.1 Observed Gravity

All gravity measurements made by the author were carried out using LaCoste- Romberg geodetic meters G240 and G826. These are highly reliable instruments which use a high stability ‘zero length’ steel spring which is thermostatically stabilised, giving a normal drift rate in the order of 0.01 mGal/day although, as discussed below, much higher drift rates are sometimes observed. Reading accuracy, that is repeatability of reading taken by an experienced operator, is also in the order of 0.01 mGal or better, however because of minor irregular variation in calibration factor the value obtained for a given gravity interval may differ by several hundredths of a milligal when different LaCoste-Romberg meters are used, or when a LaCoste-Romberg is compared with a non geodetic quartz spring meter.

In order to control the drifts, measurements were carried out in closed survey loops. The drift of the gravity measurements is defined as the difference between two readings made at different times at the same station, known as the ‘drift base station’. In a closed survey loop, measurements starts and end at the same station. This allows identification and subsequent removal of the drift within the loop. In the course of the survey described in this thesis, in which loops often extended over periods of several days, overnight drifts were recorded by taking measurements at the ‘overnight station’ in the evening when the survey was suspended and in the next morning when the survey resumed.

In the 1992 survey, the low drift rate of less than 0.01 mGal/day was recorded when surveying Mayu and Talaud in the central Molucca Sea region but larger ones were observed when measurements were made around the Banggai Islands and in the Sula Group. In the Banggai Islands survey a drift rate in the order of 0.5 mGal/day was identified when completing the survey loop at the Banggai base station. Further degradation in the performance of the instrument was noted when surveying the south

15 coast of Taliabu and Mangole, where a drift rate of about 1 mGal/day was recorded. The most probable reason for the high drift rate in the Banggai islands and the Sula Group surveys was inadequate charging of the gravity meter batteries. The electric generator which was hired from Luwuk, on East Arm Sulawesi, did not operate effectively due to shortage of spare parts. Furthermore, inadequate supplies of mains electricity in the region made it impossible to recharge the batteries from this source. This situation caused the batteries to be insufficiently charged which in turn destabilized the thermostat and degraded the performance of the gravity meter.

Figure 2.1 shows a plot of the drift of the gravity meter G240 used during the surveys in the central Molucca Sea and the Banggai-Sula . The overall drift was about 15 mGal and the main dashed line in the figure is drawn on the assumption that the drift has occurred linearly from 28 September 1992, when a measurement was made at Hasanuddin airport Ujung Pandang on the way to the survey areas, to 30 November 1992 on the completion of the 1992 expedition. However, segments of drift lines obtained in Temate, Mayu, Talaud, Peleng, Banggai, Taliabu and Mangole indicate that the drift occurred irregularly during this period, with particular high drift rates between 5* and 24^ November.

Despite the high and irregular nature of the drift, notably in the Banggai-Sula surveys, the drift within each loop was necessarily assumed to have been linear when corrections were made for stations within the loop. The effect of this is to introduce the uncertainty in observed gravity in the order of a milligal for the stations of this survey. This would be unacceptably large in most circumstances but because of the extremely large gravity difference in the Banggai-Sula area, such results are still usable. To provide some further control on these high drifts, a second visit was made to the Banggai Island in 1993. Drift corrections for surveys in Mayu and Talaud were also made on the same principle.

In the 1993 survey, an overall drift rate of less than 0.01 mGal/day was recorded. This was obtained on the basis of measurements made at Hasanuddin airport Ujung Pandang on the commencement and completion of the expedition which lasted in 21 days. This excellent performance of the instrument was probably achieved by supplying

16 the gravity meter from a pure direct current (dc) source to maintain a constant heating of the ‘sensing spring’ during the night time when not surveying. A set of 8 D-size dry cells batteries were arranged in series to provide a 12 Volts direct current source. The batteries which were used in this way lasted for about 10 to 12 hours, depending on whether a heavy-duty or regular types of batteries were used. This allowed sufficient time to recharge the primary sealed acid lead batteries so that these were sufficiently fresh in the morning when survey work started. These strategy was adopted primary because of the restricted availability of mains electric power throughout the survey area and because of the suspicion that the use of unstable mains power sources had led to the degradation of the performance of the gravity meter in the 1992 surveys. Figure 2.2 shows the drift characteristics of the G826 gravity meter used during the 1993 expedition. Although the overall drift rate was in general less than 0.01 mGal/day, the drift still occurred in an irregular fashion within this period. Most notably, the drift obtained in the Kolonodale survey loops which amounted to about 0.05 mGal/day. However, in all other cases the drift rates were of the order of about 0.01 mGal/day (Bubung and Luwuk) or less (Palu and Ujung Pandang).

In the processing of the gravity data, tide corrections which are non-linear in nature, were carried out prior to the removal of the drifts which are linear by assumption. Corrections of the tidal gravity effects were carried out using the Longman formulae (Longman 1959) and Honkasalo approach (Honkasalo 1964), implemented in the ET (Earth Tide) computer program by Almond (1986). Richard Almond was involved in a joint co-operation project between GRDC and BMR in Kalimantan (Borneo) under the auspices of the Indonesia-Australia Geological Mapping Project (lAGMP). During the implementation of the lAGMP, he coded and translated a number of computer programs which had previously run on an HP-1000 mini computer on to MS-DOS® machines at GRDC in Bandung. The Earth Tide program was slightly modified by the present author to enable interactive entry of the required variables for each station including , year, month, date, hour, longitude, latitude and elevation. Results of the computation can be displayed on the screen or printed.

17 2.2 Longitude and Latitude

Navigation on boat, land vehicles and foot traverses was by the use of topographic maps at a scale of 1:250,000 and identifying coastal and topographic features. Map at the scale of 1:250,000 was the only ones which were adequately reliable to use at the time of the surveys. These maps, which were originally sourced from the United States Army Map Services, are known as the AMS series were produced prior to 1965. These maps were also used by GRDC as base reference for compilation of gravity maps at scale of 1:250,000.

Although all stations were located on the coasts, the accuracy with which locations could be determined and plotted on the maps was not always very high, particularly on long, straight and featureless coasts such as the western part of south coast of Taliabu. In other cases where coastline was heavily indented with distinct topographic features {e.g. the southwest part of Peleng), determining and plotting a station on the map was relatively easier.

The accuracy of plotting a feature on the base maps relative to the absolute standards of longitude and latitude is much more difficult to assess. The smallest dot of a fine marker of size 0.1 millimetre has a diameter of approximately 25 to 50 metres. A dot which was produced using a 0.5 millimetres marker implies an area of about 125 to 250 metres. Therefore in a situation where a feature on the map exactly matched the situation in the field, the uncertainty of plotting the feature on the map was estimated to be about 250 metres. Difficulties in matching features on the map and situations in the field could sometime arise and these in turn magnified the uncertainty in determining and plotting stations on the base maps. Quantifying this error is very difficult, but it is estimated that the uncertainty in the location of a station in this circumstances is in the order of 500 metres. This assumes that the maps themselves are totally accurate. This is unlikely to be the case but no discrepancies were observed in the field, which can be taken as indications that the ± 500 metres error is unlikely to have been exceeded.

In the latitude of the study area (about 0° to 4°S), a change of latitude of one minute (approximately 1.85 km), corresponds to a theoretical gravity change of about 0.4

18 mGal, but changes in longitude have no corresponding effect. The uncertainty of about 500 metres which was estimated above therefore corresponds to an error in gravity anomaly of about 0.11 mGal if co-ordinate shifts occurs in the N-S direction, otherwise the error is less.

A navigation aid such as hand-held satellite receiver of the Global Positioning System (GPS) when operated in single mode would have given an accuracy of about 100 metres. Another mode of reception known as the ‘differential interferometric configuration’ using at least 3 receivers improves the accuracy into the order of sub­ metre. However, the gravity expeditions of the Sorong Fault Zone Project were not equipped with a GPS receiver and locations of gravity stations were determined visually.

2.3 Height

All gravity data acquired during the course of the Sorong Fault Zone Project were obtained at stations situated at or close to sea level and heights were referenced visually to actual sea level using a meter tape or meter stick, giving an uncertainty of about 0.1 metre in the vertical extent, which is equivalent to an error in gravity anomaly of approximately 0.04 mGal when a reduction density of 2.67 Mg.m'^ is used.

The actual sea level which were used as the reference may vary considerably throughout the study area, but since the information on the tidal gauge were unavailable, reduction of the reference level into a common datum was impossible. To a first approximation, the discrepancies may be assumed to be within the range of about 2 metres, giving an error in gravity anomaly of about 0.62 mGal. The overall error which originated from uncertainties in determining the location and elevation of a station was approximately 0.76 mGal, which is trivial if compared to the large range of gravity anomaly throughout the survey area (from -5 mGal around Kolonodale on the east coast of Central Sulawesi to +320 mGal in the western part of south coast of Mangole) and the very high gradients in most areas. The maps which accompany this thesis are contoured at interval of 10 mGals or greater.

19 In the case of surveys in Irian Jaya, the heights of stations were determined by using height differences computed from differences in barometric pressure. For the purpose of a reference, the theory of this is presented in Appendix E, in which it is demonstrated that, in a dry atmosphere where temperature decreases with height at a uniform rate (a constant lapse rate), the difference in height //between two points having pressure po and Pi \s given by

x^

H = ^^^ (2.1) g

where x = — — (2.2) Po g is the acceleration due to gravity 0 is the mean temperature of the air column between the two points r is the gas constant per gram

In the Irian Jaya surveys pressures were measured using aneroid barometers. These instruments can be read to the nearest hundredth of a millibar which is equivalent to an elevation range of 0.1 metre, but readings are repeatable only to about five hundredths of a millibar. Absolute readings are unreliable and it is necessary to recalibrate at intervals under laboratory condition to obtain values of po.

The ‘single base’ method of observation was used, the field and base barometers were read simultaneously at the base station at the start and finish of each set of observations and the base barometer was read at intervals of fifteen to twenty minutes throughout the intervening period. This method is normally satisfactory provided that field observations are made less than 30 km from the base station, that there is no significant pressure gradient between the field station and base, that a number of points of known height are occupied and that not more than two hours elapses between repeat readings at base with the field barometer. Because of difficulties associated with the Irian Jaya operation, all these rules were violated, the most serious obstacle being the lack of usable known heights within the survey area and the heights were therefore determined from ‘sea-level’ stations.

20 A correction has also to be made for humidity (Crone 1948). Measurements of the humidity were carried out at base station only, using wet and dry bulb thermometers. Barometric leveling in a tropical region such as Irian Jaya is relatively easier than in regions at higher latitudes. The behaviour of air masses in the tropics is more regular and predictable than in any other part of the globe. A typical example of an observed tropical diurnal pressure curve (Milsom 1971), with a peak at about 0930 and a minimum at about 1630 local time is shown in Figure 2.3. Although in no case was it possible to monitor an entire diurnal curve simultaneously at two stations, the regularity of these curves allows some general comparison to be made between those observed at different places on different days. From these comparisons, and from consideration of the closure diagram of the network of stations with repeated readings some conclusions were drawn by Milsom (1971).

First, the significance of sea breeze was emphasized. Sea breezes (and the corresponding, but weaker, land breezes at night) occur because of the difference in thermal capacity and conductivity between land and sea. In day time, because the land surface heats faster than the sea, the temperature of the near-ground air column increases and it expands, resulting in an increase in pressure at all heights above ground level. The upper air excess pressure is relieved by seaward air flow at height, which in turn results in a lowering of sea level onshore pressure relative to the pressure out to sea. The lowering of pressure at an inland station is at its greatest in mid-afremoon and so tends to emphasize the diurnal minimum. The amplitudes of diurnal pressure curves at low-lying inland bases were commonly 4 to 5 millibar, one millibar or more higher than the average for coastal bases.

A second important effect which was apparent from comparison of the diurnal pressure curve obtained at difference bases concerns the relation between temperature observed on the surface and the temperature of the ‘free’ atmosphere. As is shown in Appendix E. If the lapse rate was uniform the mean temperature of the air column may be used without errors in calculating the height. In practice, the mean of the temperature at the base and field stations is usually used.

21 As ground temperature usually rises until about 1500 local time, it would be expected that the pressure difference between low and high stations would be a minimum at that time, implying that the amplitude of the diurnal curve should decrease with altitude. Comparison of the diurnal curves shows that while this is to some degree valid, the effect is significantly less than would be expected from the observed temperatures; in fact, because of sea breezes, the amplitude of the curves obtained at high inland bases are often greater than those recorded on the coast.

Land and sea breezes are well understood in meteorology, and a number of theoretical analyses have been made (Haurwitz 1947, Schmidt 1947) but despite this, there is little experimental data were published on the accompanying pressure changes. It is likely, however, that at about 0900 local time, the distribution of pressure in the atmosphere over the land and the sea is approximately in a balance so that barometric leveling involving stations close to a coast should be carried out at or near this time. However, once again practical considerations prevented this being done in Irian Jaya surveys, measurement continues throughout the day. Elevation errors may therefore be expected to be in the order of 5 to 10 metres in mountainous areas, equivalent to a 1 to 2 mGal error in Bouguer anomaly. Detailed analysis of the errors has not been carried out within the context of this thesis, since discussion of the gravity in Irian Jaya is based on the published GRDC-BMR map (Dow et al. 1986).

2.4 Accuracy of the Gravity Map

Although exact figure on the accuracy of the gravity data acquired during the course of the Sorong Fault Zone Project was difficult to assess, on the basis of the discussion in Section 2.2 and 2.3, an estimation of errors which do not exceed 2 mGal appeared to be acceptable. Accuracies of gravity information which originated from other sources were even more difficult to quantify, since published materials concerning these information often do not detail the analyses or results of the analyses on the accuracy of the data. Apart from being left with uncertainty in the accuracy of information in the published materials, the processing of the data from previous surveys often used different reduction formula. Moreover, data reduction may have been incorrectly carried

22 out in the sense that the use of one formula was made but links were made to a reference value computed using another formula.

In one case, gravity information which originated from previous surveys in Central Sulawesi (Silver et al. 1983) were incorrectly reduced. The use of the 1930 normal gravity formula was made by Silver et al (1983) to carry out the reduction of their data but links were made to the national gravity base stations network which were computed on the basis of the IGSN 1971 (Milsom pers. comm. 1994). In order to bring the 1983 data in line with the Sorong Fault Zone Project data, recomputation on the data were carried out (Milsom pers. comm. 1994) and ultimately, links to the Sorong Fault Zone Project surveys were made by the author during the 1993 expedition. In this respect therefore, the accuracy of the Central Sulawesi gravity data (Silver et al 1983) is regarded similar to the Sorong Fault Zone Project gravity data which is not in exceed of 2 mGal but original accuracy of the 1983 surveys is not known, possibly also in the order of about 2 mGal.

The accuracy of in-land surveys of Obi mentioned in Chapter 1 is estimated at about 2 mGal if the heights were measured barometrically but possibly better if optical leveling were used.

On Bum Island, immediately to the south of the study area, the only published gravity information is in the form of gravity profile. No location is given for this profile but statement was made that the interpretation was carried out for western part of the island. By identifying the orientation (N-S) and the length of the profile (approximately 70 km), it was deduced that the profile must cut across the central western part of Bum Island. This profile has been used to provide control over the gravity contouring in the Bum region but uncertainties are clearly very large and the quantification on this would be impossible.

Gravity map of Seram published by Milsom (1977) has been incorporated in this study. All stations were at sea level and the overall error in the Bouguer anomalies are estimated at less than 2 mGal (Milsom pers. comm. 1995).

23 Gravity data of Kepala Burung Irian Jaya (Dow et al. 1986) has been as well integrated into the present study. Coastal stations may be accurate within less than 2 mGal but in the mountainous areas the uncertainties in the Bouguer anomalies may be well in exceed of 2 mGal level possibly higher. However, the configuration of the measurement network which consists of interlocking loops enabled optimization on the Bouguer anomalies to be performed, giving an accuracy of less than 2 mGal or better (Barlow pers. comm. 1980).

Gravity data firom marine coverage prior to the introduction of GPS navigation are notoriously unreliable and crossover error for the tracks firom different surveys very fi-equently exceed 10 mGal (Wessel and Watts 1988). The overall accuracy of marine firee air gravity map of Bowin et al (1980) therefore not be very high but probably compatible with the 25 mGal contour interval being used in this study.

The vastly improved satellite-derived firee-air gravity maps of offshore areas based on ERS-1 altimetry become available too late for incorporation in this study but would in any case have added a little in an area which is relatively well covered by conventional marine gravity measurements. The along track accuracy claimed for the ERS-1 data is about 5 mGal or better.

24 KEY: SORONG FAULT ZONE PROJECT 1992 Mayu, Talaud and Banggai-Sula Gravity Surveys 1J40.962 Gravity reading

1740 T ------Drifts at base stations 1740.962

------Overall drift

Talaud T.29 Base station T 1755

Ujung Pandang BG.1

1730 -1840^^—•'m o ■■ 1750 - 1915 BG.O Mayu O' Banggai 1726.300 BG.O 1835 1835 1745 TaliatHJ 1910

Mayu Peleng

1720 J- 1780 1830-^ 1 7 4 0 -L 1905

Mangole

1 1775 1900

Ternate Talaud Banggai-Sula

30 30 September October

Figure 2.1 The G240 gravity meter drift recorded during the surveys in the Central Molucca Sea and the Banggai-Sula regions.

-1 7 8 0 1773.632 1773.749 o ------o

Ujung Pandang

•1760 SORONG FAULT ZONE PROJECT 1993 East Coast Central Sulawesi Gravity Surveys

KEY:

-1 7 4 0 1J04.135 Gravity reading

Drifts at base stations

Overall drift -1 7 2 0 Kolonodale Base station

1704.135 1704.366

Bubung Kolonodale -1 7 0 0 1696.049 1696.453 «------_ ------^ ... . . 1693.955 o -o o o- Luwuk

1681.409 1681.359 ■1680 o------o------o Palu

•1660

Figure 2.2 The G826 gravity meter drift obtained during the surveys on the east coast of Central Sulawesi.

25 KEY : - 1010 Base barometer curve

Field barometer at base

Field barometer at station 6615.0044

Field barometer at station 6615.0004

Field barometer at station 6615.0046

Relative drift line, base to 6615.0004

Relative drift line, base to 6615.0046 - 1008

- 1006

Time (hours)

08:00 10:00 12:00 14:00 16:00 18:00

Figure 2.3 Typical diurnal variation of barometric pressure (After Milsom 1971). Chapter 3 GRAVITY REDUCTION AND INTERPRETATION TECHNIQUES

3.1 The Reduction of Gravity Data

Gravity reductions are attempts to remove or reduce the effect on observed gravity of causes which are not of immediate geological interest. The reduction procedure attempts to convert the gravity measured at a point on the surface of the earth to the one which would have been measured at the point on a reference surface which is vertically above or below the true point of measurement. The ideal reference surface is known as the geoid (Fig. 3.1) and is defined as the gravitational equipotential surface coincident with mean sea level (e,g. Lambeck 1988). In land areas the position of the geoid is difficult to define, since it has to be computed from gravity measurements {e.g. Li et al. 1995), and the Earth ellipsoid, a much simpler surface, is usually taken as the reference.

The procedure of the reduction of gravity data of the Sorong Fault Zone Project consisted of the latitude correction, the free-air correction and the Bouguer correction. Some discussion on the isostatic correction and corrections to sea surface measurements are also included since this study used marine data (Bowin et al. 1980) and data from earlier surveys in Irian Jaya (Dow et al. 1986) in which isostatic effects are large. However the details of the reductions applied to the marine surveys (Bowin et al. 1980) were unavailable and data from surveys in Irian Jaya were obtained in the form of Simple Bouguer gravity values. The various types of corrections are discussed below in order to supplement the descriptions of each stage of the reduction procedure. Although, as already noted, no attention has been given to isostatic and topography- related corrections in this study so far, it will be desirable in the future to apply these corrections when more reliable topographic data and bathymetry become available.

In the procedure of the reduction, the computed anomalies represent a measure of the deviation of the gravity field from the fields due to idealised models of the Earth

27 of increasing complexity. In the latitude correction stage, the observed gravity gp obtained at a point on the surface P (Fig. 3.2) is reduced by subtracting the theoretical gravity at the same latitude on the ideal Earth ellipsoid. The correction thus has form

Sq ^ S p -Ys 3.1

where ys is the theoretical gravity computed at the surface of the reference ellipsoid.

At this stage the intermediate result gg represents the simplest form of gravity anomaly, portraying the gross deviation of the gravity field of the real Earth from that of the simplest Earth model, the ellipsoid.

It can be argued that the latitude correction should also take account of the difference in elevation between the geoid and ellipsoid in the form

Yq = Ys- (dy/dr)N 3.2

N represents the height of the geoid above the ellipsoid.

However uncertainties as to the actual location of the geoid prevent this second order correction being applied since the quantity yq contains an unknown parameter N, the geoid height. The justification for neglecting the corrections can be provided in terms of the geoid height anomaly which can be computed using the approximation suggested by Fowler (1990, p. 176-179). To illustrate this, in the Airy isostatic model vyith sea water, crustal and mantle densities of 1.03,2.67 and 3.07 Mg.m'^, respectively, and reference crust 30 km thick, the geoid height N for on-land stations of height 77 is

N « 5.72 H (0.6 + 0.07675H) metres 3.3 where 77 is the elevation of an on-land station expressed in kilometres. Thus a compensated mountain range 2 km high would result in a positive geoid anomaly of

28 about 9 metres which is equivalent to a discrepancy of about 1.8 mGal in the theoretical gravity value which should be subtracted from the theoretical value. Likewise, the geoid height N for an Airy compensated ocean basin of depth d is given by

N a -3.51 d (0.6 - 0.051 d ) metres 3.4 where d is expressed in kilometres. Therefore, a compensated ocean basin 5 km deep would result in a negative geoid height of approximately 6 metres which is equivalent to a discrepancy of approximately 1.2 mGal which should be added to the theoretical gravity value

Since interpretation of the results of the gravity surveys of the Sorong Fault Zone Project was concerned with very large anomalies (10 mGal contour interval) and very steep gradients (several mGal/km in many cases), and since most stations were established close to sea level, these discrepancies are of very minor significance and have been ignored. In cases where surveys were carried out inland, with stations where heights varied considerably from sea level to mountain ranges of about 2000 metres, e.g. the Irian Jaya surveys (Dow et al. 1986), the distances of the stations from the reference ellipsoid implied the existence of a correction to the international formula. However, this correction is still small in comparison with anomaly sizes and survey accuracy and has again been neglected. Furthermore, isostasy in these regions is still a subject of debate; applying the geoid corrections would introduce more uncertainty to the interpretations.

The fact that the point of measurement P is not on the geoid/ellipsoid, which was an assumption of the latitude correction, is taken into account in the free-air correction stage, i.e. the elevation of the point at which measurements were made is considered. This reduction compensates for the fact that the gravitational attraction decreases with distance from the centre of the Earth and hence with height above the geoid. At this stage the results of the reduction (the free-air gravity) represents not merely the deviation of the gravity field from the simplest Earth model (the Earth

29 ellipsoid) but begins to take account of the effect of gravity field on variations of elevation above the geoid.

The effects of topographic masses remain after the free-air correction has been applied and these are removed in the so called two-stage approach consisting of the Bouguer correction and the terrain correction. In the Bouguer correction the effects of topographic masses above the reference surface are approximated by the effect of a horizontal slab of infinite extent with thickness equal to the height of the station (the Bouguer slab). The resulting anomaly is called the simple Bouguer gravity, representing a model which accounts for mass distribution between the earth's surface and the geoid by assuming no topographic undulation in the region surrounding the observation point. The results of the Sorong Fault Zone gravity surveys have been reduced only to this point, which is adequate in view of the large anomalies and steep gradient encountered.

The assumption that the topography corresponds to a Bouguer slab, which is horizontal and extends infinitely in all directions away from the gravity station, is obviously incorrect. For maximum accuracy, allowance should be made for the effect of the actual topography, and also for earth curvature. Terrain corrections allow for any deviation in topographic height from the upper surface of the Bouguer slab. The correction for the Earth curvature which compensates for discrepancies between the infinitely horizontal Bouguer slab and the slightly curving Earth's surface can be very significant in mountainous areas {cf. St. John 1967) but is negligible for the stations established during the Sorong Fault Zone Project, which were all at or close to sea level.

The effect of lateral density variations caused by surficial and near-surface geological features is sometimes also included. Application of terrain and, where necessary, curvature corrections results in the extended Bouguer gravity, giving a final gravity field value which is largely free of effects of mass distributions between the Earth's surface and the reference surface (the geoid). A number of further reductions can be applied to gravity data and are also described in this chapter since it may be desirable to apply them to the Sorong Fault Zone data at some future date.

30 Although it would be possible to make corrections directly for the effect of topography above the reference surface without first computing for the effect of the Bouguer Slab, it is mathematically simpler to evaluate the effect of the Bouguer Slab and then compensate for deviations of topography from the upper surface of the Bouguer Slab. A peculiarity of this two-stage approach is that terrain corrections are always positive. The mass of the hill A above the gravity station P (Fig. 3.2) exerts an upward attraction on the gravity meter, and the correction is clearly positive (added to the observed field). The valley B lies in a region that the calculation on the Bouguer Slab assumed to be filled with rock mass, the gravitational attraction of which would have had a downward component. The correction must therefore allow for over­ correction by the Bouguer Slab and is again positive.

Isostatic corrections may be applied according to some assumed isostatic compensation model (e.g. Airy compensation by depressing or elevating the Moho, or Pratt compensation by density changes throughout long columns extending down to a deep isopiestic level). When this correction is applied, the result of the reduction is called the isostatic gravity, representing gravity field model in which topographic masses are supported by buoyancy forces. Isostatic effects may be large but because of the large number of possible ways in which compensation may be achieved, they are best allowed for in the interpretation stage.

The reduction of the gravity data of the Sorong Fault Zone Project to simple Bouguer anomaly was carried out using the Quattro Pro^^ Version 4.0 spreadsheet program which runs under MS-DOS® Version 5.0 available in the Regional Geology Laboratory of the Department of Geological Sciences, the University College London. An example of the spreadsheet for the reduction of the gravity data is included in Appendix B. Details of the reductions which have been, or might be, applied to other data from the Sorong Fault Zone are discussed in the sections which follow. The contents of these sections are summarised below (Table 3.1).

31 Table 3.1 Corrections applied in the procedure of the gravity data reduction of the Sorong Fault Zone Project

Section Correction Applied (?) Comment 3.1.1 Latitude Applied Essential 3.1.2 Free-air Applied Essential, but station heights are small except in Irian Jaya 3.1.3 Bouguer plate Applied Essential, but station heights are small except in Irian Jaya 3.1.4 Terrain Not applied Topography poorly defined by available maps, measurements at or close to sea level 3.1.5 Isostatic Not applied Isostatic mechanism unknown, investigated via modelling 3.1.6 Geological Not applied Investigated via modelling

The special problems presented by data collected on surface ships are discussed in Section 3.1.7.

3.1.1 The latitude correction

The latitude correction is applied to remove the effect of the earth's ellipticity. At the surface of a uniform, biaxial ellipsoidal earth, the gravity field g would be given by an equation of the form

3.5 where go is the equatorial gravity, (j) the latitude and a and b are constant. The latitude corrections for the gravity data of the Sorong Fault Project were carried out using the 1967 formula which may be written as

g = 978031.85 ( 1 + 0.0053024sin'^- 0.0000059siri^2ip) mGal 3.6

Although based on a reference ellipsoid which is now being replaced by an improved model known as WGS 84, it was felt that a change would be pointless for the present study since the best fitting Earth ellipsoid will not be determined until the whole of the

32 Earth's surface has been covered by regional gravity surveys. The differences between the 1967 formula and WGS 84 produces differences in normal gravity no more than 1 mGal at any point on the global reference surface, and this is trivial for the 10 mGal and 25 mGal contour intervals used in this study. Moreover, any change in latitude formula might also require a change in base station values, i.e. the IGSN 1971 values at these stations might no longer be appropriate. Problem of this type have frequently arisen with the use of the 1967 formula to reduce data based on a Postdam system base station, or of the 1930 formula to reduce data based on IGSN 1971. The original data from Central Sulawesi supplied by Professor Silver (Silver, pers comm 1993) was an example of the latter type of error.

It has been proposed by O'Keefe and Kaula (1964) that instead of referring gravity measurements to the real earth, the hydrostatic figure be used, therefore relating the anomalies more directly to the existing state of stress. Departures from this figure can, therefore, be attributed to departures from the hydrostatic stress state of the earth i.e. deviatoric stresses within the earth body {e.g. Lambeck 1988). Again, given the uncertainties and approximations implicit in the very regional interpretations presented in this thesis, such complications need not be considered here.

3.1.2 The free-air correction

The free-air correction is applied to compensate for variations in the distance of gravity stations from the Earth's centre; in common practice sea level is considered as the reference surface approximating to the geoid (the equipotential surface at mean sea level) and the height of the station above or below this level is used in the calculations. The effects of topographic masses are ignored and individual free-air anomalies are therefore strongly dependent on elevation. However, if the topography is isostatically compensated, i.e. if there is no net mass excess or deficiency in the Earth's uppermost layers, the integral of free-air anomaly over a sufficiently large area should be zero. Non-zero average of free-air anomalies therefore indicate departures from local isostatioc equilibrium.

33 The derivation of free-air correction, is given by Heiskanen and Vening Meinesz (1958, p. 148), who show that

gF=2^h{\-~-) 3.7 r 2r where gm is the force of gravity midway between the point of measurement and sea level and r is the local radius of the earth. The first term in this equation amounts to about 0.3086 mGal.m'\ The second term in the Equation 3.7 is almost negligible being only about 0.07 mGal.m'^ at 1000 metres altitude but at altitudes over 2000 metres the effect becomes significant. For instance, at 2000 metres the second term amounts to approximately 0.3 mGal.m'^ and at 5000 metres it reaches about 1.7 mGal.m'\

A less often considered question concerns the application of the terrain corrections to free-air anomalies and the related difficulties introduced by local changes in earth curvature (Milsom 1971). Whether or not a terrain correction should be applied depends entirely on the definition of free-air anomaly adopted, but since anomaly maps are normally used to investigate the state of stress in the earth, it may be thought desirable that the integral over a wide area in which isostatic equilibrium prevails should be zero. St. John (1967) pointed out that corrections should, strictly speaking, be applied for the effects of topographic masses above the level of the station, as these masses lie outside the closed surface to which Green’s theorem may be applied. In addition such masses may be compensated isostatically by mass deficiencies at depth. In this case both the excess mass (above the observation point) and the deficit mass (below the observation point) affect the gravity field at the station in the same sense and the combined effect may be significant. Terrain corrections for stations situated on mountain peaks and broad valleys may be negligible (St. John 1967). Valleys below the level of the station do not necessitate a terrain correction to the free-air anomaly on any system since both the mass deficit and any compensation at depth lie within the Green’s theorem surface. In cases where a station is located at the bottom of narrow river valleys (Milsom 1971), a terrain correction has sometimes been applied by assuming an Airy type isostatic compensation of the external topography. The effect of the

34 correction is to increase the value of the free-air anomaly computed for low-lying stations in mountainous areas, and therefore to reduce to some extent the very steep gradients normally associated with the unsmoothed anomalies. The correction appears valid in terms of the requirement of zero free-air integral in stable areas, but individual values may differ significantly from those of free-air anomaly as normally obtained. In this thesis the more common definition of free-air anomaly is adopted and terrain corrections have not been applied.

Errors in free-air anomaly arises from inaccuracies in the measurement of both gravity field and station height; as discussed in the previous chapter, the errors in gravity measurements in the Sorong Fault Zone Project were small and can therefore usually be ignored in comparison with errors due to inaccurate elevations. The probable error in elevation of stations situated close to sea level is of the order of two metres, corresponding to approximately 0.62 mGal in free-air correction.

Even if a region is in a state of complete isostatic equilibrium, the gravitational effects of the topographic masses and their compensation at depth do not cancel for the surface observations, although this condition may be approached in extensive plateau areas. The inverse square law and directional effects ensure that the field due to large surface masses is dominant near the gravity station and that the field due to the compensation becomes relatively more important as distance increases. In this respect the most effective part of the topography is that which lies directly between the geoid and the gravity station. The higher the station, the greater the mass involved, so that free-air anomalies normally show a positive correlation with height are extremely sensitive to changes in height and gradients are large and unrelated to changes in underlying geological structure. Accordingly it is normal practice to smooth onshore free-air anomalies prior to contouring, the cut-off value of the smoothing filter being usually determined by the 'wavelength' of the topography. A commonly used smoothing filter is the sine function (Bracewell 1965) given by the equation

sin nx ^ Ç smcx = ------3.5 nx

35 A perfect smoothing filter should not introduce errors, although, as in any averaging process, some of the initial information is lost. If the distribution of the observation points is irregular, aliasing errors may be introduced (St. John 1967). Because of the difficulties associated with interpreting free-air anomalies onshore, they have not been used in this thesis. The free-air correction has been applied simply as an intermediate stage in the reduction to Bouguer anomaly.

3.1.3 The Bouguer correction

The Bouguer correction was developed by Bouguer (1749) as a simple correction for the effect of the rock masses lying between the point of observation and the reference surface. As noted above, these masses are the primary cause of the very high gradients observed in unsmoothed free-air anomalies. For a wide range of topography the gravitational effect of the Bouguer model, an infinite horizontal slab of uniform density, is very close to reality, as can be demonstrated by some simple calculations.

Firstly it can be shown that the gravitational effect Ag of a cylinder ring element at any axial point (Fig. 3.3), distance h and H (h

Ag = 2!rpG [ ] 3.9 where G = 6.673x10-11 m^kg''s'^ is the gravitational constant, /othe density of the ring and r and R the inner and outer radii respectively. This equation is valid whether h and 77 are measured in the same direction or not, since only even powered terms are involved. The physical reality underlying this mathematical result is that the effect at the origin of the element from -h to +h is always zero. With the notation shown in Fig. 3.3, the above equation can be rewritten as

36 Ag = 2npG (k + l-m-n) 3.10

For the Bouguer Plate both r and R are zero, and the difference between (if+R^) and

R approaches zero as R approaches infinity, giving the simple Bouguer plate formula

g B = 27rpGH 3.11

An idea of the effect of deviations of the terrain from the Bouguer Plate can be obtained by comparing this expression with the field at the centre of the upper surface of a finite disc. Table 3.2 shows the relationship between the ratio between R/Hand g / g B .

Table 3.2 Relationship between R/H and g / g B

R/H g/gB 50 0.99 10 0.95 5 0.90 1 0.58

Since gB is itself directly proportional to //, the difference in milligals between g and gB increases rapidly with increase in the height of the block, for constant radius.

The model used above is, for certain, far from realistic, and in particular makes it easy to forget that topographic relief is as significant above the station as below it. For coastal stations, it is almost always topography above the level of the station which is important. Since excess masses above station level and mass deficits below both result in an attenuation of field at the station, corrections for deviation of the topography from the Bouguer Plate are always positive and never cancel. It is quite useful to compare the field due to a right circular cone at its own apex (Fig. 3.4) with gB, remembering the results can be applied to a station at the top of a conical hill or at the bottom of a conical depression.

37 Referring to Fig. 3.4 the gravity field at the apex due to the laminae of thickness dh may be obtained using the following equations

dg = iTtpG ((h + dh)-h-l+n) 3.12

now 1-n = dh siri(p thus dg = 2npG (1 - sin

g = 2npG ( 1 -sin

The following table shows the relationship between ^ and g / g B

Table 3.3 Relationship between andg/g^

g^gB 35' 0.99 2°50' 0.95 5°25' 0.90 25° 0.58

Numerically the difference is proportional to h.

In regions of low relief the simple Bouguer correction provides a satisfactory approximation to the effects of elevation and topography, provided only that an appropriate density is used. If this is not done the resulting Bouguer anomalies will remain markedly dependent on elevation, Nettleton's method of determining the bulk density of near surface rocks (e.g. Nettleton 1939) being based on this fact. Simple Bouguer anomaly maps based on unsuitable value of density can be very misleading if elevations vary widely and large changes occur in lateral density, but do serve important purpose. Since the simple Bouguer anomaly is derived solely from an assumed and constant density and from the four principal facts (longitude, latitude, height and observed gravity) of the gravity station, the original data can in principle be recovered from the anomaly map. This will not be the case if further assumptions and corrections

38 are introduced. Useful re-interpretations have often been made on the basis of simple Bouguer anomaly maps when the original data have been lost or destroyed and the production and wide circulation of such maps still represents an important safeguard. The fact that all gravity stations in the Sorong Fault Zone Project were read within a few metres of sea level virtually eliminates the effect of density contrasts in the topography as a source of error in interpretation.

3.1.4 Terrain correction

Terrain correction is an attempt to compensate for irregularities of topographic surfaces above and below the level of the Bouguer Plate discussed above. The gravitational effect of masses above the Bouguer Plate as well as of depressions below the level of the plate {i.e. the station height) is to reduce the value of the observed gravity at the station. Since the Bouguer Plate was assumed to have a flat surface the computed gravitational effect of these discrepancies must be added to the observed gravity {i.e. terrain corrections are always positive).

The classical method for carrying out terrain corrections is to use a transparent Hammer Chart (Hammer 1939) overlain on a topographic map at a compatible scale and centred on the gravity station under consideration. The difference between the average height of the terrain and the station height is estimated for each compartment. Software suites are available for carrying out this routine {e.g. Kane 1962, Milsom 1971, Ballina 1990, Ma and Watts 1994) and can to some extent speed-up the computation but the lack of digital topographic data at suitable intervals demands the laborious digitisation of the topographic maps in and surrounding the survey areas. Without digital topographic data {i.e. without a Digital Terrain Model), performing terrain corrections is equally time-consuming whether automatic (using a computer) or manually (using the Hammer Chart). As a result, for small scale surveys where no Digital Terrain Models are available, the classic method of using Hammer Chart is still widely and conveniently used.

39 Although mathematically simple, the computation procedure in terrain corrections is tedious. In principal, the terrain correction for a gravity station is written in terms of a gravitational attraction of a cylindrical shell experienced at a gravity station situated at the axial point of the cylinder; and the overall correction for a station is obtained by summing up all gravitational effects of each shell surrounding the station extending to a predefined radial distance. The use of the term shell in this context refers to a particular compartment of a radial zone if the computation is carried out using the Hammer Chart or to an elemental prism of predefined size and radial distance if computation of terrain effect is done using computer programs (e.g. Kane 1962, Takin and Talwani 1966, Milsom 1971, Zhou et al. 1990, Ballina 1990, Ma and Watts 1994). As has already been noted, anomaly Ag due to a cylinder shell at an axial point is given by

Ag = 2jrpG [ (H^+R^) - (h^+R^) * + (h^+R^) ] 3.14

A first requirement to solve this eqiTftion is that the relative magnitudes of the parameters h, H, r and R should be known. If a cylinder is to be used to approximate to the actual topography, it is known that, in the outer three zones at least, the heights will inevitably be very much smaller than the radii. It is much rarer for the average topographic level at a given distance from an observation point to differ from the height at that point by more than the distance of separation (Milsom 1971), i.e. consistent and sustained topographic slopes of more than 45° are rare. Attention should be paid to the fact that beyond a certain distance from the gravity station, the effect of the Earth’s curvature should be taken into consideration, i.e. at distances in excess of about 30 km the zone radii are always much larger than the mean topographic height (Milsom 1971). However, curvature corrections are significant only for stations at siginificant elevation above sea level and are therefore not necessary for stations of the Sorong Fault Zone survey. Since 'Extended' Bouguer anomalies are obtained by correcting for deviations of the actual land surface from the Bouguer plane, a vast amount of additional topographic information must be used. Use of this data, whether by approximating contour lines by

40 polygons or by estimation of the average height of topographic blocks, is at least partly subjective.

Although the main purpose of the Bouguer and, more particularly, the Extended Bouguer, correction is to reduce the dependence of the contours on station elevation, it must be realised that, because of density variations in the superficial crustal layers, this never be done completely. The reason for this is illustrated in Figure 3.3. The extended Bouguer anomaly relates the gravity observations at A and B after removal of the effects of the topography above the geoid. The mass inhomogeneity if not included in these calculations, represents a source of error. However, masses such as 7, below the reference level, are not considered in the reduction calculations and their effect forms a valid part of the computed anomaly. Clearly the field due to 7 at ^ will be different from the field at B, also from the field at on the reference surface (which cannot certainly be measured). This implies that one can never say that the Extended Bouguer, or any other, anomaly represents a reduction to the reference level. The elevation of the point of observation cannot be altered by any reduction process, and where this is likely to be an important factor it should be allowed for in interpretation. In the case of the Sorong Fault Zone surveys (except Irian Jaya), location of virtually all stations close to sea level effectively eliminates this problem.

If either station height varies largely or topographic relief undulates ruggedly, topographic effects may be significant out to distance at which the 'flat earth' approximation (implicit in the Bouguer assumption) is no longer valid. Corrections for earth curvature are less conceptually simple than might appear at first glance; carried to a logical conclusion terrain corrections would have to be extended around the whole earth and be applied to the theoretical field of a spherical shell, twice the field of a Bouguer plate of the same thickness. However a shell with thickness equal to the station height would be a very poor approximation to reality, firstly because the mean elevation of the Earth's surface is very close to zero and secondly because most deviations from zero level are compensated by mass change at depth. For distant points the effects of surface irregularities and their compensation are very nearly equal. Maps of the combined effect of topography and its assumed isostatic compensation at all

41 points on the globe are published by the Isostatic Institute of the International Association of Geodesy (Kârki et al 1961). These maps ignore all topographic-isostatic effects from sources within 166.7 km of the observation points {i.e. 1!4° of latitude, the outer radius of the Hayford zone O) and are based on the assumption that topographic changes are compensated by changes in the depth of a major density discontinuity at about 30 km below the geoid (the Airy isostatic assumption). For these distant corrections the exact nature of the isostatic model used is not very important.

3.1.5 Isostatic effects

Isostatic corrections represent attempts to allow for the effect of compensation of the local as well as the distant topography. The masses being considered are generally within a few tens of kilometres from the point of calculation but even so the vector of their gravitational attraction makes only a small angle with the direction of the earth's main gravitational field. Under these conditions the value of the correction is critically dependent on the nature of the isostatic model used. Two main classes of assumption have been made, the continuous (Pratt model) and the discontinues (Airy model), but the discovery of the Mohorovicic seismic velocity discontinuity (Moho), and its identification as the boundary between the earth's crust and mantle, led to the virtual abandonment of the Pratt model. Early observations of seismicity showed a strong correlation between topographic height and depth to Moho. Since a significant increase in velocity almost certainly indicates a significant increase in density, the Airy model appeared to be proven correct. More recently, seismic refraction studies have directed attention towards the variations in mantle velocity at the Moho. Woolard (1968) had shown that for the continental of the United States a simple relation between surface elevation and crustal thickness can be established only where mantle velocity lies in the range between 8.0 and 8.2 km.s"\ In other areas a correlation is observed between thin crust, crustal uplift and low mantle velocity, implying reduction in mantle density. Possibly the transfer of mass between crust and the upper mantle may be a second important mechanism for maintaining isostatic equilibrium. In some cases the

42 compensation approaches that proposed by Pratt, with the topographic mass supported by a density deficiency throughout an extended column.

As yet there have been no determinations of mantle velocity made in the study area and the most recent work on refraction seismic studies near the East Arm Sulawesi and the Banggai Islands regions (McCaffrey et al. 1981) indicated a maximum velocity of only 6.5 km.s'^ which was interpreted as representing the granitic basement of the region (McCaffrey 1981). However, a number of measurements made around the Solomon Islands (Furumoto et al 1970) showed variations from a low of 7.3 km.s"^ to a high of 8.5 km.s'^ east of the islands. This suggests, by analogy with the North American observation mentioned above, that isostatic adjustment in this area are not made only by lowering of the Moho.

A further weakness of the conventional isostatic anomaly is that no allowance is made for the compensation of mass excesses or deficiencies present in the upper crust. The distribution of such variations is seldom sufficiently understood for corrections of this type to be practicable, even if the computation time involved were not prohibitive, and as a results isostatic anomalies are of very limited use in areas of strong density contrasts.

As the Sorong Fault Zone occupies a region in which terranes of various affinities juxtaposed to eacl% other, implying strong density contrast throughout most of the region. This suggests that isostatic anomalies may not be very useful to use for studying this particular region. Isostatic corrections have therefore not been used, but isostatic effects are critically important consequences of the models being employed.

3.1.6 Geological correction

The geological correction is an attempt to allow for the effect of a sub-geoidal mass distribution (usually a sedimentary basin). The geology of an area is seldom well enough understood for the purpose of this correction to be made with any confidence.

43 The geology of the Sorong Fault Zone is at present still a subject of controversy and applying this correction would therefore have been misleading. A variant of the geological correction may be applied to marine gravity to allow for the thickness of the water layer, as discussed in the next section.

3.1.7 Correction for shipborne observations

In the discussion above an assumption has been made that the gravity observations are taken on the ground surface. However, a large number of gravity measurements are now made on-board surface ships and some results of this type (Bowin et al. 1980) have been used in this study. In one respect these data are easier to handle than those obtained on land, since the measurements are all made at sea level and, after instrumental and acceleration corrections have been made, the fi*ee-air anomaly is obtained directly by the application of the latitude correction. However these ftree-air anomalies are critically affected by sea floor topography and a number of so called Bouguer reductions have been proposed to eliminate or reduce this effect. Most involve 'replacing' the layer of sea water with that of an equivalent volume of rock of some specified density, the actual density chosen being the subject of controversy. Perhaps the most common assumption is to use the mean density of upper crustal rock (2.67 Mg.m'^) but in oceanic areas there is much to be said in favour ot the choice of the mean density of the sea floor basalt (2.80 Mg.m'^). Previous gravity work in east of the East Arm Sulawesi and north of Banggai Islands (Silver et al 1983) used a density of 2.80 Mg.m'^ as the mean density for modelling the crustal structure in this area. In the present study, however, a choice of the standard value of 2.67 Mg.m'^ has been made for reduction of the gravity data and modelling of crustal structures in the Sorong Fault Zone.

Since the mass deficiency in the sea water is compensated entirely or in part by a rise in level of the Moho, 'infilling' of the sea with material of higher density results in Bouguer anomalies which are strongly positive. The characteristics of the marine Bouguer correction have been discussed by Vajk (1964), who proposed a method of

44 reduction which he refers to as the 'modified free-air anomaly*. Essentially this is an anomaly calculated with reference to sea level for land stations and to a standard sea floor in the ocean. Corrections are made only for deviations from these conditions, assumptions being made as to the bulk density of bathymetric features. The major deviation is represented by the continental margins and in such areas a model continental margin is to be fitted to the observed bathymetry, removing from this the effect of sea bed relief. However, as has been demonstrated by a multitude of seismic refraction studies {cf. Drake 1966), continental margins are rarely simple structures and the essentially two dimensional app roach used by Vajk (1964) can seldom be applicable. This is particularly true in tectonically active areas such as the Sorong Fault Zone and the surrounding region.

3.2 Interpretation Techniques

The interpretations of the gravity field in this thesis are based on the technique known as forward modelling, in which a geological model is designed and the corresponding gravity field is computed. This field is compared with the observed field and the model is adjusted until the computed and observed fields are in close agreement. At this stage, the computed model may or may not represent the appropriate solution; in other words, a model may or may not be geologically plausible. Ambiguity does exist in the modelling work {e.g. Skeels 1947, Roy 1962), implying that a number of models may satisfy a given observed field, but only a few may be possible approximations to the geological section under investigation. Other constraints such as bathymetry, depth information from boreholes, isopach maps, sea-bottom morphology and seismic profiles may be used to provide controls on the geometry of the model. The present study used bathymetry, isopach maps and seismic profiles to provide some control on the geometry of the models. The forward modelling approach implies that models may be created either using the digitiser, or drawn directly on the screen using the mouse or entered manually using the keyboard; in all cases, the software evaluates the field response due to the models and displays it graphically on the video screen. In

45 the modelling described here both models and data were entered into the computer manually.

The interpretations in this study used the forward modelling approach as implemented in a potential field modelling software package which is copyrighted as the GM-SYS™. The package is available commercially from Northwest Geophysical Associates, Inc., PO Box 1036 Corvallis - Oregon 97339, USA. This software runs on any MS-DOS machine equipped with a processor or processors capable of performing floating-point operations, EGA or VGA graphics and a mouse as a pointing device and a plotter.

Many aspects of the implementation in the GM-SYS™ are inherited the principals of the work by Talwani et al (1959) although the software makes use of the algorithms described by Won and Bevis (1987). The Talwani et al (1959) method is based on the field due to two-dimensional (2-D) bodies, le. bodies which are oriented at right angles to the gravity profile being inspected, have infinite strike length and can be described by cross-sections of polygonal shape. In detail, the technique relies on the transformation of the field equation from surface integrals to line integrals so that the field introduced by each polygon is determined by the summation of terms each of which is associated with a single side. The gravity field of such bodies are reasonable approximations to the fields produced by bodies in which the the along-strike dimension is at least three times as great as the cross strike dimension. Cady (1980) presented an approach to three-dimensional (3-D) models based on the 2-D models with limited strike length. The strike length may be different on opposite sides of the profile and the equations even allow for bodies to be completely offset fi*om the profile. This technique, now universally known as the two-and-a-half (2!4-D) modelling, forms the bases of the Won and Bevis (1987) programs.

Methods proprietary to the Northwest Geophysics Associates Inc. have been used to improve the efficiency and speed of the system so that it is suitable for use in an interactive graphical computing environment. Hardcopy of models may be obtained

46 directly when a plotter is connected to the computer. Alternatively, graphics metafiles may be produced and reprocessed for production of reports.

The GM-SYS™ modelling system accepts both absolute density and relative density values for analysing models. However, absolute density values correspond to absolute gravity fields, quantities which are not of interest in the present study; relative density values {i.e. density contrasts) were therefore used in the analysis and this strategy gives compatible magnitudes of the gravity field in the study area.

The GM-SYS™ program package is capable of computing both gravity and magnetic fields 'simultaneously' (although the program allows the user to view only either the gravity field or the magnetic field at any one time) and interactively, permitting changes to be made to subsurface geological models whilst the computed fields are displayed graphically on the computer monitor screen and are adjusted in ‘real-time’ as changes are made to the models. The present study only utilised the gravity modelling option, since no magnetic measurements were made during the course of the Sorong Fault Zone Project. It would be desirable in the future to combine gravity with magnetic modelling when on-land or airborne magnetic data become available.

The majority of the gravity analyses presented in this present study were based on the 2-D approximation, the extreme E-W elongation of gravity contour lines in the Sorong Fault Zone indicating that 2V2-D modelling would be pointless and that it would, in any case, be difficult to determine realistic strike lengths. However, for models of the gravity fields in the Sulabesi, Banggai and Obi areas, where Bouguer anomaly contours adopt more elliptical forms, the 2-D and 216-D responses have been compared. The differences even in these cases are minor and almost certainly smaller than the errors introduced by the use of very simplified geological models.

47 Mountainous area

g e o id a l e le v a tio n - -

h : height of station K norm al d : depth of point M to ellipsoid N : geoid height

F igu re 3.1 A diagram showing relationship between the geoid, ellipsoid and topography (source: Verma 1985).

Topography

hill Bouguer Slab (assumed) Earth Curvature V v a lle y

F igu re 3 .2 A diagram illustrating various elements described in the gravity reduction (see text for explanation). Simplified from Verma 1985.

48 o

F igu re 3.3 A diagram showing the geometry for the computation of the gravitational effect of a cylindrical ring element at a point O (after M ilsom 1971).

7K

F igu re 3 .4 A diagram showing the geometry for the computation of the gravitational effect of a right circular cone at a point O (after M ilsom 1971).

49 Geoid-—

Figure 3.5 The mass inhomogeneity X should be removed to obtain the Extended Bouguer Gravity, but not Y,

50 Chapter 4 TERRANE GEOLOGY OF THE SORONG FAULT ZONE

4.1 Introduction

The oblique convergence between the Eurasian, Philippine Sea and Australian plates results in intricate sliver tectonics which have led to the complex terrane distribution in the Sorong Fault Zone and the surrounding region (Fig 4.1). The area surrounding the Sorong Fault Zone has been described in terms of a great number of distinct terranes which are believed to have formed and evolved in a variety of environments {cf. Pigram and Davies 1987, Letouzey et al. 1983). A broad distinction can be made between terranes which are believed to be underlain by old (Palaeozoic or older) continental crust and those formed in an oceanic environment, partly as a consequence of arc volcanism. Terranes with continental affinities are recognised to originate chiefly from the northern margin of the Australian continent. The oceanic terrane units may be further subdivided into terranes which are thought to have been derived from the Plate and those which are associated with ocean basins further north, such as the Philippine Sea Plate. Arc terranes in the Sorong Fault Zone are derived mainly from the Philippine Sea Plate. The amalgamated terranes, as the name implies, are composed of terranes with various affinities and are often intensely tectonised. Dispersion and amalgamation of these terranes have involved strike slip movements along the various elements of the Sorong Fault Zone, and the strands of the fault now form many of the terrane boundaries. One tectonic model which accommodates such distribution is that proposed by Charlton (1986), which is shown in Fig 4.2.

In the discussion which follows, the Sorong Fault Zone is defined (Hall et al. 1987) as the zone which includes the region extending from the Kepala Burung of Irian Jaya in the east to eastern Sulawesi in the west (Fig 1.2). In the Kepala Burung area, the Sorong Fault is a clearly defined zone of left-lateral faulting with an average width of approximately 10 Km (Tjia 1973). Even in this region, however, the situation is

51 complicated by the additional presence of the sub-parallel Koor Fault to the north, which Pigram and Davies (1987) considered to be more important terrane boundary. Both faults terminate in the east against the NNW-SSE Ransiki Fault, which is taken as marking the eastern limit of the project area. Left lateral transcurrent faulting is important throughout the remainder of New Guinea (Milsom 1985) but its discussion is beyond the scope of this thesis. To the west of Sorong, the Sorong Fault continues offshore but branches and splits to form the Molucca-Sorong Fault, the North Sula- Sorong Fault, the South Sula-Sorong Fault and the Bum Fracture (Hall et al. 1987, Tjokrosapoetro and Budhitrisna 1982). At the western end, the fault zone terminates in the fold and thmst belts of the eastern Sulawesi. To the north, the zone is juxtaposed against the Molucca Sea Collision Zone. To the south, the zone is adjacent to the Banda Arc. Most of this area is covered by sea, making it impossible to identify faults directly by visual means. However, bathymetric contour lines of the region (Fig. 4.3) show lineations which may indicate the existence of fault strands or terrane boundaries. The consequences of the lateral movements are readily recognised on a number of the islands, allowing the continuations of the fault zone to be traced in regions covered by sea. Peculiarities in the shapes of the various islands and juxtapositioning of islands with distinct contrasts in geology clearly indicate strike slip movements. For example, the EW-trending Sula Island group, which comprises Taliabu, Mangole and Sulabesi, is geographically close to Sulawesi but lithologically has greater affinities with Kepala Burung. Studies of the seismicity and other geophysical data have also allowed the various strands of the fault zone to be located more accurately (Hamilton 1979, Silver et al. 1983, Letouzey et al. 1983), although by Indonesian standard the area is one of low seismic activity.

In this chapter the characteristics of the individual strand of the fault zone are described first, followed by descriptions of terranes which they separate.

52 4.2 Fault Strands of the Sorong Fault Zone

Although most of the Sorong Fault Zone is covered by water, geophysical studies i.e. reflection seismic {e.g. Letouzey et al. 1983, Silver et al. 1983), marine free- air gravity (Bowin et al. 1980) and bathymetry (Mammerickx et al. 1976), have all confirmed the existence of the Sorong Fault Zone and strands which are derived from it. The generally east-west orientation of contour lines of both bathymetry (Fig. 4.3) and gravity field (Fig. 6.1) indicate distinct east-west oriented features which may be interpreted as representing the fault zone. Interpreted seismic profiles (Fig. 4.4 and Fig. 4.5) have also clearly shown the location of various strands of the Sorong Fault Zone. A more recent marine expedition by the RRS Charles Darwin Cruise CD30 (Masson et al. 1988) deployed, besides other marine scientific apparatus, the GLORIA long range sidescan sonar system for imaging sea-bottom morphological features. Coverage was obtained over some parts of the Sorong Fault Zone (see Chapter 5 of this thesis).

Strands of the fault zone recognised in this study include the Sorong Fault, the Koor Fault, the Molucca-Sorong Fault, the North Misool-Sorong Fault, the Buru Fracture, the Seram Trough, the North Sula-Sorong Fault and the South Sula-Sorong Fault (Fig. 1.2 and Fig. 4.1).

4.2.1 Sorong Fault

In the northern part of Kepala Burung area (Fig. 4.6), Sorong Fault (Visser and Hermes 1962) forms the boundary between continental crust of the Australian Plate in the south and Mesozoic bathyal shales and Mid Miocene volcanics similar to those along the northern flank of the New Guinea central ranges (Tamrau terrane; Pigram and Davies 1987). In the west, near the township of Sorong, the fault forms a zone of left- lateral strike slip faulting having width of approximately 10 km (Tjia 1973) and containing large blocks of various rocks of both continental and oceanic affinities (Dow and Sukamto 1984). Offshore west of Sorong, the fault zone continues but is covered

53 by sea. However, a distinct ENE-WSW oriented lineation in the extreme north of Salawati may be interpreted as representing the continuation of the fault zone (Pigram and Davies 1987). This zone of left-lateral faulting extends WSW as far southwest as offshore south of the Raja Ampat Islands (Fig. 1.2) where the zone splits into two major fault strands, the North Molucca-Sorong and the North Misool-Sorong faults.

4.2.2 Koor Fault

The boundary between the oceanic crust of the Pacific Plate and the New Guinea continental margin sediments appears to be represented by the Koor Fault (Pigram and Davies 1987, Dow and Sukamto 1984), situated on the extreme north of the Kepala Burung, approximately 30 km north of the Sorong Fault (Fig. 4.6). Geological mapping (Dow and Sukamto 1984) has confirmed that the ENE-WSW oriented Koor Fault forms the boundary which separates the Mesozoic trough-type sediments and the overlying Middle Miocene intermediate and acid volcanics of continental affinities from island arc volcanic rocks of the Pacific Plate.

Koor Fault extends ENE-WSW covering a distance of about 100 km and may continue offshore west. The narrow strait between Salawati and Islands separates two terranes similar to those separated by the Koor Fault and logically therefore marks its continuation. The strait continues as a narrow region of deep water passing south of the Raja Ampat Islands into the Seram Sea (Milsom pers. comm. 1995). The western termination of the Koor Fault Zone may be a merger with the Sorong Fault west of Salawati but this only on a speculative interpretation since no direct evidence is currently available.

54 4.2.3 Molucca-Sorong Fault

West of Salawati Island at about 130°E; 1°S, i.e. immediately south of the Raja Ampat Islands (Fig. 1.2), the Sorong Fault is believed to split into two strands, forming the Molucca-Sorong Fault and the North Misool-Sorong Fault, which are prominent tectonic features in this region {e.g. Letouzey et al. 1983). The Molucca-Sorong Fault extends as far as the region southwest of Bacan Island where the fault intersects a north- south oriented thrust belt, the West Halmahera Thrust, which covers a distance of almost 300 km.

On bathymetric maps (Fig. 4.3) the Molucca-Sorong Fault appears to be delineated by the 1000 m contour line in the marine area between Bacan and South Halmahera to the north and Obi to the south. A narrow bathymetric trough about 100 km long northeast of Obi appears to be the expression of this fault zone. The north- south oriented lineation of the 1000 m water depth contour line northwest of Obi may indicate, although only to a limited extent a conjugate element of the fault zone, running north-south. However, this feature should be further verified since the argument is purely speculative. The narrow bathymetric trough widens towards the west as it passes south of Bacan Island to the point where the Molucca-Sorong Fault intersects the West Halmahera Thrust. Acute turning edges of bathymetric contour lines southwest of Bacan indicate abrupt changes in water depth which may be interpreted as marking the area of intersection between these two features.

On the seismic profiles (Fig. 4.4) interpreted by Letouzey et al. (1983), the Molucca-Sorong Fault is represented by bathymetric depression reaching almost 3 s TWT on the deepest trough i.e. about 2200 m (profile 1). These troughs (profile 1, 2 and 3) are bounded by moderate to gently sloping seafloor, a geometry which suggests that they may indicate a zone of transtensional faulting, a characteristic feature of a strike-slip regime at a releasing bend (Park 1989, Reading 1980).

55 4.2.4 North Misool-Sorong Fault

The North Misool-Sorong Fault occupies a zone which extends southwest from the area where the principal Sorong Fault Zone splits. It extends approximately 100 km before it diverges into three other strands in the area midway between Misool and , forming the Buru Fracture, the North Sula-Sorong Fault and the South Sula- Sorong Fault (Fig. 1.2).

On the bathymetric map (Fig. 4.3) the North Misool-Sorong Fault Zone appears to be delineated by a NE-SW oriented sea-bottom depression represented by the 1000 m contour line of water depth. Letouzey et al (1983) recognised the North Misool-Sorong Fault on the interpreted seismic profiles (Fig. 4.4, profiles 1, 2 and 3) as a narrow bathymetric ridge at about 3 s TWT on profile 1, about 1 s TWT on profile 2 and a relatively flat sea-bottom feature at about 1 s TWT on profile 3. This interpretation of the North Misool-Sorong Fault is associated with a positive bathymetric feature and implies that it may form a zone of transpressional faulting (Park 1989, Reading 1980).

4.2.5 Buru Fracture

The Buru Fracture (Tjokrosapoetro and Budhitrisna 1982) extends southwest from an area midway between Obi and Misool islands (Fig. 1.2). On the bathymetric map (Fig. 4.3) this fracture zone is rather obscured but appears to be delineated by the NE-SW trending 2000 m and 3000 m contour lines off northwest Seram. Seismic images across the fracture zone were not available for the present study and interpretation of sidescan sonar GLORIA images (see Chapter 5) does not provide strong evidence for the occurrence of the Buru Fracture. The interpretation by Tjokrosapoetro and Budhitrisna (1982) was presumably made on the basis of surface geology which they extrapolated offshore to argue for the existence of the Buru Fracture.

56 4.2.6 Seram Trough

The Seram Trough extends WNW from approximately 50 km offshore northwest of west Seram (Fig. 1.2) and swings SE offshore west of Onin Peninsula in the Kepala Burung area. On bathymetry (Fig. 4.3) the trough appears to be delineated by the depression represented by the 1000 m contour line and deepens as it approaches its western termination east of Sulabesi. On the interpreted seismic profiles of Letouzey et al. (1983) the Seram Trough is clearly defined as a sea-bottom depression reaching to more than 4 s TWT (Fig. 4.4). The southern part of the trough is characterised by intensely deformed sediments forming north-dipping thrust packets but to the north, a thick sequence of relatively undisturbed sediments (about 2 s TWT thick) rests on acoustic basement at about 5 s TWT depth.

4.2.7 North Sula-Sorong Fault

Passing south of the Obi Island (Fig. 1.2), the North Sula-Sorong Fault extends westwards and continues as far west as northeast Mangole before it transmutes into a zone of thrusting, the Sula Thrust, (Letouzey et al. 1983, Silver et al. 1983). On bathymetry (Fig. 4.3) the North Sula-Sorong Fault and the Sula Thrust appear to coincide with the 1000 m contour line which runs parallel to the north coast of Mangole and Taliabu and as far west as a major strike-slip fault, the Greyhound Strait Fault (Hamilton 1979) which separates Taliabu from the Banggai Islands. Silver et al. (1983) interpreted the Sula Thrust as a zone of moderate to low-angle thrust faulting (Fig. 4.5), which brings the tectonic melange of the Molucca Sea onto the Banggai-Sula Microcontinental Platform (see Section 4.5.1).

The interpreted seismic profiles (Fig. 4.4 profiles 1, 2 and 3) showed that the North Sula-Sorong Fault is represented by a sea-bottom depression reaching to more than 2 s TWT (profiles 1 and 2). On profile 3 however, the fault zone is less distinct than on profiles 1 and 2. The depression is bounded on both sides by moderate to gently

57 sloping seafloor, which can be interpreted as representing a zone of transtensional faulting (Reading 1980, Park 1989).

4.2.8 South Sula-Sorong Fault

The South Sula-Sorong Fault separates from the North Sula-Sorong Fault immediately south of Obi and appears to extend as far west as the NW-SE oriented Greyhound Strait Fault (Fig. 1.2) west of Taliabu. Defining the path of the fault is complicated by the presence of the north-south oriented island of Sulabesi. The fault may pass between Sulabesi and Mangole but Charlton (1995) suggests that it actually suffers a right lateral offset along a transfer fault which coincides with Sulabesi. This question is further considered in Chapter 5, which deals with the sidescan sonar data and in the discussion of the gravity modelling (Chapter 6). The fault continues across the Greyhound Fault as far west as the area southwest of Peleng, as suggested by the 1000 m bathymetric contour line and the steep bathymetric slope (Fig. 4.3). It may therefore form the entire terrane boundary which separates the Banggai-Sula continental fragment from the North Banda Sea terrane (Fig. 4.1). Seismic profiles were not available in this area and the interpretation was made chiefly on the bathymetric information. Gravity modelling in this region also is analysed in Chapter 6.

4.3 Oceanic Terranes

Possible sources of oceanic terranes within the Sorong Fault Zone and the surrounding region include the Indian Ocean and the Philippine Sea oceanic crusts. However, neither of the two oceanic terranes which are recognised in the fault zone, the Molucca Sea and the North Banda Sea terranes, appear to have come from either of these . The Molucca Sea represents the remnant of a formerly much larger ocean now almost entirely subducted, whereas the origin of the North Banda Sea terrane remains ambiguous.

58 4.3.1 Molucca Sea Collision Zone

The Molucca Sea Collision Zone is situated in a region of complex interaction between the Eurasian, Australian and the Philippine Sea plates and is composed largely of intensely deformed sedimentary rocks. Hamilton (1979) noted that the rocks which underlie the Molucca Sea are acoustically irresolvable. Katili (1975) recognised that subduction zones exist adjacent to the Sangihe and Halmahera arcs facing the Molucca Sea, and considered that the deformed trench fills may have been responsible for the irresolvability of seismic images in this region. Isostatic gravity anomalies reaching as low as -200 mGal (Vening Meinesz 1948) indicate either that there are anomalously low densities of crustal or mantle material beneath the region, or considerable thickness of sedimentary rocks. More recently McCaffrey and Silver (1980) studied seismic refraction profiles in the region and found that an approximately 15 km thick low- velocity layer (collision complex) occurs beneath the 2 km water depth of the Molucca Sea. They suggested that this collision complex can account for the free-air anomaly, which reaches values as low as -250 mGal in the southern part of the region.

The on the east and Sangihe arc on the west are both active and face towards the Molucca Sea. Two Benioff zones which dip away from the Molucca Sea are clearly defined by earthquake focal depth information in the region (Fig. 4.7). The east-dipping Benioff zone results in the active volcanic arc of western Halmahera. The active Sangihe volcanic arc is the direct consequence of the west-dipping Benioff zone. The magmatic arcs of Halmahera and Sangihe are separated by approximately 250 km at the closest distance. The active volcanoes of the Halmahera arc are situated immediately west of the west coast of Halmahera in the central part of the island, and immediately onshore in the northern part of the island. The active volcanoes of the Sangihe arc are located as far south as the northern tip of the island of Sulawesi. The north and south arms of Sulawesi are composed of inactive arc volcanics. Nearly continuous volcanic activity has been inferred from about the Early Miocene up to Quaternary time (Sukamto 1975). The East Sangihe Thrust and the West Halmahera Thrust form the west and east boundaries of the Molucca Sea Collision Zone and are marked by troughs 3000 m deep bordering the arcs along the sides facing the Molucca

59 Sea. The East Sangihe Thrust separates the collision zone from the North Sulawesi arc- volcanic terrane, whereas the West Halmahera Thrust isolates the collision zone from the West Halmahera-Tamrau arc terrane. The two thrusts should be regarded as superficial features developed during collision and not as the surface traces of the subduction zones. The southern boundary of the collision zone is the Sula Thrust along which the Molucca Sea collision complex overrides the Banggai-Sula Microcontinental Platform.

The north-trending central region of the Molucca Sea Collision Zone is a broad bathymetric high, the Talaud-Mayu Ridge, on which the Talaud, Mayu, and Tifore islands emerge above sea level. Exposures of peridotite and gabbro were found on the various islands during the course of the Sorong Fault Zone Project, indicating up- thrusting of slices of mantle material above sea level. Local gravity highs reaching to more than +100 mGal on Mayu and +200 mGal on Talaud (Sardjono 1992) marks the occurrence of high level slices of mantle material. A crustal and lithospheric gravity model of the Molucca Sea collision zone proposed by McCaffrey and Silver (1980) is shown in Fig 4.8. Shallow earthquakes are concentrated beneath the crest of the ridge and indicate a predominance of thrust type focal mechanism (Fitch 1970).

4.3.2 North Banda Sea

The North Banda Sea terrane occupies a region in the north-western part of the Banda Sea Basin (Fig. 4.1). It is bounded in the north by the South Sula-Sorong Fault which separates it from the Banggai-Sula Platform. A strand of the Tolo Thrust forms the west and southwest boundaries and isolates the North Banda Sea terrane from the East Sulawesi Ophiolite province and the Central Sulawesi Metamorphic belt. The Banda Ridge (Sinta Ridge; Réhault et al 1991) in the south (Fig. 1.2), forms the southern boundary and separates the North Banda Sea terrane from the South Banda Sea Basin. The eastern boundary of the North Banda Sea terrane is largely formed by the island of Buru, which is believed to be a detached portion of the Australian continent (Pigram and Panggabean 1984).

60 Réhault et a/. (1991) recognised the North Banda Sea terrane as part of the Banda Sea oceanic crust. Bowin et al. (1980) suggested that the Banda Sea might be a trapped fragment of oceanic crust of Cretaceous-Eocene age originally part of the Argo Abyssal Plain northwest of the Australian continent. The oceanic crust of the North Banda Sea would therefore be expected to have characteristics similar to Indian Ocean crust. Based on the patterns of marine magnetic lineations in the Banda, Sulawesi and Sulu basins, Lee and McCabe (1986) claimed that these basins were a continuous feature in the Cretaceous to Early Tertiary time and that the various islands which either arrived at their present position as a result of middle to late Tertiary tectonic movements or emerged as a result of the Neogene subduction, have dissected and isolated the continuous ocean basin into its present configuration (Fig 4.1).

If the sliver kinematics of the tectonic model proposed by Charlton (1986) are valid, only the southern and south-eastern parts of the Banda Sea are underlain by Indian Ocean crust (Fig. 4.2). The northern and north-western parts of the Banda Sea could, therefore, be underlain by oceanic crust which originated from the Philippine Sea Plate. However, on the basis of geochemical analyses and radiometric age dating of rock samples (± 6 Ma, Late Miocene to Early Pliocene) dredged from the floors of the North and South Banda Sea basins, Réhault et al. (1994) concluded that the two basins are of similar nature. Furthermore, they hypothesised that the North and South Banda Sea resulted from the same process of back-arc opening during the Late Neogene. These basins are now separated by the NE-SW trending Banda Ridge, of continental in character, from which samples of Triassic platform carbonate were dredged (Réhault et al. 1994). The continental sliver Banda Ridge may have originated at the northern margin of the Australian continent and have been translated by the left-lateral movement of the Sorong Fault into its position separating the North Banda Sea terrane from the South Banda Sea basin. If so, it possibly reached the present position before spreading commenced.

61 4.4 Arc Terranes of the Philippine Sea Plate

Arc terranes in the Sorong Fault Zone originated primarily from the interaction between the Philippine Sea Plate and the northern margin of the Australian Plate (Hall et al 1987). Convergence at the plate boundaries resulted in the development of volcanic island arcs. These are recognised as the West Halmahera-Tamrau terrane, the East Halmahera-Waigeo terrane (Fig. 4.1) and the Arfak terrane; the latter is located in the extreme northern part of Kepala Burung (Fig. 4.6).

4.4.1 West Halmahera-Tamrau Terrane

The West Halmahera-Tamrau terrane is defined here as occupying the region covering the Northwest and Southwest Arms of Halmahera and the recent volcanic islands immediately to the west of the west coast of Halmahera (Fig. 4.1 and Fig. 4.9). It extends to the east to include Batanta, north Salawati and the northern part of the Kepala Burung. The West Halmahera thrust to the west forms the western boundary of the terrane, isolating it from the Molucca Sea terrane. The Molucca-Sorong Fault to the south represents the southern boundary, separating the West Halmahera-Tamrau terrane from the Obi province and terranes in the Kepala Burung region. On Halmahera, the eastern boundary of the West Halmahera-Tamrau terrane is a suture zone situated in the central area (Fig. 4.9). This is a zone of strong deformation in which Neogene rocks have been locally and intensely deformed (Hall et al 1987). The West Halmahera- Tamrau terrane extends northward to the eastern part of the Philippine volcanic belt (HalUra/. 1987).

The West Halmahera-Tamrau terrane consists mainly of pre-Late Cretaceous island arc volcanic and volcaniclastic rocks (Hall et a l 1987). These rocks form the basement of the province and are unconformably overlain by Late Miocene-Early Pliocene sedimentary rocks which record events in the transport of Halmahera westward along faults which may be related to the present day Sorong Fault Zone. The basement rocks consist of calc-alkaline volcanic rocks, intrusive igneous rocks and

62 volcaniclastic units containing similar calc-alkaline debris. Lithologically, these rocks are andésites, andesitic breccias and conglomerates. The typical volcanic basement rock is represented by the Oha Volcanic Formation (Hakim and Hall 1991).

4.4.2 East Halmahera-Waigeo Terrane

The East Halmahera-Waigeo terrane (Sukamto 1986, Hall et a l 1987) occupies a region covering the Northeast and Southeast Arms of Halmahera, Waigeo island and numerous small islands between these two including Gebe and Gag (Fig. 4.1). The central suture zone marks the western boundary of the terrane, separating it from the West Halmahera-Tamrau terrane (Fig. 4.9). To the south, the East Halmahera-Waigeo terrane is bounded by the Molucca-Sorong Fault, isolating it from the Obi terrane. It is presumably separated from terranes in the Kepala Burung region by a fault south of Waigeo. The entire terrane forms a part of the Philippine Sea plate.

The East Halmahera-Waigeo terrane is composed of ophiolitic basement complex consisting of a complete sequence, with the possible exception of the sheeted dykes, of ophiolite members ranging from ultramafic rocks, cumulates and microgabbros, and volcanic rocks. Radiolarian cherts are common as float in areas of exposed ophiolites. Metamorphic rocks are also found, including foliated amphibole and minor blueschists. The plutonic igneous rocks include diorites and lesser granitic rocks (Hall et al 1987). These rocks form the basement of the Southeast and Northeast Arms of Halmahera and probably underlie the entire region between Halmahera, Waigeo and North Obi (Charlton and Partoyo 1991, Hakim and Hall 1991). Peridotites include abundant serpentinized harzburgites and rare Iherzolites. The harzburgites record evidence of a high degree of partial melting of the mantle and are similar to those of oceanic forearcs. The Iherzolites, in contrast, are less depleted than the harzburgites, and are compatible with a mantle residue after the extraction of mid- oceanic ridge basalts (Hall et al 1987). Cumulates are common and consist of dunites, olivine clinopyroxenes, wehrlites and olivine gabbronorites. These indicate moderate to high degree partial melting of mantle materials. Chemical and petrological data show a

63 genetic relation between cumulates and harzburgites. Hornblende-rich diorites and trondhjemites which intrude the microgabbros have no genetic relation with the ophiolite pluton. Two phases of Late Cretaceous arc-related igneous activity were identified from "^°Ar/^^Ar dating of diorite hornblende. Volcanic rocks in the ophiolite complex include boninitic rocks and amygdaloidal calcalkaline basalts. These rocks have a composition similar to those of ocean island volcanic rocks and seamounts (Hall etal. 1987).

The basement rocks of Waigeo island (Fig. 4.10) consist of lithology similar to ophiolites found in East Halmahera and also are in a similar stratigraphie position and of similar age (Charlton and Partoyo 1991). The ophiolites of Waigeo include all members of the sequence from ultramafic rocks, through cumulates and microgabbros, to volcanic rocks. These rocks form the basement of western and central Waigeo and possibly underlie the entire island. The upper contact between the basement and the younger sequence is always an unconformity or a fault. The basement rocks of Waigeo are composed of deformed and extensively serpentinized ultrabasic rocks including dunites and harzburgites with smaller quantities of gabbros, dolerites and basalts. A large proportion of the ultramafic rocks have cumulate textures, and represent the lower part of a layered sequence. The western part of the island is composed predominantly of serpentinites and the north coast of the island shows massive exposure of similar rocks. The age of the ophiolitic rocks on Waigeo is not known. Massive and brecciated serpentinites are unconformably overlain by sandstone of the Upper Eocene Lamlam Formation. The age of the basement complex is suggested to be a Jurassic or older (Hall e ta l 1987).

4.4.3 Arfak Terrane

The Arfak Terrane is named after the Arfak Mountains in northeastern Kepala Burung (Fig. 4.6). It has been dismembered and forms a number of subterranes, which are found on Biak, Yapen, and Num Islands at the head of the Sarera Bay, and in the Arfak and Tosem Mountains in northern Kepala Burung. The Arfak Mountain

64 subterrane is separated from the Kemum terrane on the southwest side by the Ransiki Fault Zone. The terrane extends offshore to the east and is covered by Late Cenozoic sediments. In northern Kepala Burung, it is separated from the Tamrau terrane to the south by the Koor Fault Zone and Neogene sediments. The terrane is composed of Upper Eocene to Middle Miocene basaltic to andesitic lava, breccia and tuff, and is intruded by dykes and stocks of dolerite and gabbro. The volcanic rocks are overlain by Early to Middle Miocene limestone. This terrane is interpreted as an island-arc complex (Pigram and Davies 1987).

4.5 Continental Terranes

Terranes with continental affinities in the Sorong Fault Zone include the Banggai-Sula Platform, the Buru-Seram Microcontinent, the Misool terrane, the Kemum terrane and the Netoni terrane. These provinces are thought to have originated at the northern margin of the Australian continent and to have rifted away during the break-up of Gondwana. Dispersion and distribution of these terrane blocks partly resulted from the left-lateral movement of the Sorong Fault which translated them into their present positions.

4.5.1 Banggai-Sula Platform

The Banggai-Sula terrane comprises the Banggai Archipelago, the Sula island group and the intervening water covered region of the Salue-Timpaus strait. It stands on a narrow ridge which trends eastwards from Sulawesi. The islands are parts of a small fragment of continental crust which emerge above sea level. The Banggai-Sula terrane constitutes a micro-continental platform which is clearly delineated by the 1000 m bathymetric contour lines shown in Fig 4.3 (Hamilton 1979).

A strand of the Sorong Fault, the North Sula-Sorong Fault south of Obi, which transforms into the Sula Thrust north of Sula Platform (Letouzey et al 1983), marks the

65 northern boundary of the Banggai-Sula Platform, separating the Banggai-Sula Platform from the Molucca Sea Collision Zone and the Obi terrane. The South Sula-Sorong Fault marks the southern boundary of the Banggai-Sula terrane and separates it from the North Banda Sea basin and the Buru-Seram Microcontinent. The Batui thrust, to the west, represents the collision front of the Banggai-Sula Platform and marks its western boundary, separating the platform from the northern part of the East Sulawesi terrane.

The Banggai-Sula terrane consists largely of metamorphic basement of the Palaeozoic age (Van Bemmelen 1970, Hamilton 1979, Pigram and Panggabean 1984) intruded by Permo-Triassic granites and overlain by contemporaneous acid volcanics (Fig. 4.11). The basement complex is unconformably overlain by continental to shallow marine coarse-grained elastics of the Early Jurassic formations (Garrard et al 1988) which in turn is conformably overlain by black, restricted marine shales and claystones of Late Jurassic to Early Cretaceous formations. On Taliabu and Mangole, the latter formation is overlain by deep-water carbonates of Cretaceous age and elsewhere platform limestones rest unconformably on the older formations (Garrard et al 1988). Coral conglomerates of Quaternary age occur widely throughout the Banggai-Sula region. The deposition of this sequence is believed to have initially taken place within a rifr-graben setting, then in a restricted shallow marine environment and finally, after considerable subsidence, in open deep water marine conditions (Garrard et al 1988).

The metamorphic basement, which is widely exposed on West Peleng, Banggai, Labobo, Bangkurung, Salue Besar, Taliabu, Mangole and Sulabesi, consists of slates, schists and gneisses which probably underwent some degree of deformation during the Early Palaeozoic. During the Late Permian to Early Triassic the basement was intruded by granites. The higher degrees of metamorphism produced by these intrusions are in part homfels. Dating on schist from Peleng (Sukamto 1975) yielded Carboniferous age.

The intrusive rocks comprise mainly of red orthoclase-rich granite, granodiorite, microdiorite, syenite porphyries, aplite and pegmatite (Garrard et al 1988). Dating using K-Ar on hornblende and Rb-Sr on feldspar extracted form the granite (Pigram and Panggabean 1984) have indicated Permian to Triassic age. The Mangole volcanics

66 (Garrard et al 1988) of about 1000 m thick exposes on Banggai, Taliabu and Mangole and consist of rhyolite, dacite, ignimbrite, lithic tuff and breccia. Dating of volcanic specimens (Sukamto 1975) have yielded Permo-Triassic age, indicating an approximate co-magmatic with the Banggai granite.

4.5.2 Buru-Seram Microcontinent

The Buru-Seram micro-continental terrane is represented by the islands of Bum, Seram, Ambon and other smaller adjacent islands (Fig. 1.2 and Fig. 4.1). The Seram Trough forms the northern and eastern boundaries of the terrane, and separates it from terranes in the Kepala Burung area and amalgamated terrane of Obi to the north. The strong N-S lineation of the bathymetric contour west of Bum (Fig. 4.3), an expression of a submarine escarpment, forms the western boundary of the terrane, separating the microcontinent from the North Banda Sea basin. The South Sula-Sorong Fault represents the northern boundary of the Bum-Seram terrane, and isolates the Bum- Seram terrane from the Banggai-Sula Platform.

The Bum-Seram terrane is composed largely of crystalline rocks including granitic and metamorphic units (Fig. 4.12). The northern part of Bum consists of biotite granite, gneiss and mica-schist. The basement of Seram is represented by a variety of metamorphic rocks (Hutchison 1989). These rocks are overlain by a sequence of well bedded micaceous siltstone and mudstone of Triassic age, interlayered with micaceous sandstone. The Bum-Seram microcontinent originated in the north-east sector of the former Australian Continental margin, and detached itself by the Middle Jurassic to collide with the Kepala Burung continental fragment in mid-Tertiary times and was subsequently translated westwards (Pigram and Panggabean 1984).

67 4.5.3 Misool Terrane

The Misool terrane is a small continental block which is largely covered by water. Parts of the block emerge on Misool Island and the Onin and Kumawa peninsulas of the southern part of Kepala Burung (Fig. 4.6). The block is bounded to the south and southeast by the Seram Trough. The boundaries between the Misool and Kemum and the Misool and Lengguru terranes are covered by Miocene and younger sediments of the Salawati and Bintuni Basins.

The Misool terrane consists of a Palaeozoic basement of isoclinally folded and metamorphosed turbidites, unconformably overlain by an almost complete sequence of Mesozoic sediments (Pigram and Davies 1987). This sequence is composed of Triassic turbidites, Late Triassic shallow-water limestone, Early Jurassic to early Late Cretaceous bathyal mudstone and limestone, which is tuffaceous near the top, and Late Cretaceous fluvio-deltaic elastics and nodular limestone. Palaeogene rocks are dominantly shallow-water carbonates. The pre-Miocene section was folded in the Late Oligocene to Early Miocene (Pigram and Davies 1987).

4.5.4 Kemum Terrane

The Kemum terrane is a large continental block occupying most of the Kepala Burung region south of the Sorong Fault Zone (Fig. 4.6). The block is separated from the Arfak terrane to the east by the Ransiki Fault Zone. It is partly overthrust at the southeastern margin by the Lengguru terrane. At the southern margin, the block is covered by Miocene sediments of the Bintuni and Salawati successor basins.

The Kemum terrane is composed of Siluro-Devonian turbidites, which were isoclinally folded and metamorphosed in the Late Devonian or Early Carboniferous and were intruded by Early Carboniferous and Permo Triassic granitoids. This crystalline basement is overlain by Middle Carboniferous to Late Permian shallow marine paralic siliciclastic sediments. The Mesozoic section is thin, incomplete and locally absent.

68 Jurassic to Triassic beds overlie the Palaeozoic rocks and are in turn overlain by Cretaceous shallow marine sediments. The Late Cretaceous to Early Eocene was marked by the local development of evaporitic sediments, and the Eocene section comprises mainly limestone. This sequence was folded in the Late Oligocene (Pigram and Davies 1987).

4.5.5 Netoni Terrane

The Netoni terrane is a small terrane in northwestern Kepala Burung, which is named after Netoni Mountain, adjacent to the Sorong Fault Zone (Fig. 4.6). The terrane is faulted against the Tamrau terrane on the northern side, and the Kemum Terrane on the south. It is composed of Late Permian to Early Triassic granitoids, ranging in composition fi*om quartz syenite to diorite and adamelite (Pigram and Davies 1987).

4.6 Amalgamated Terranes

Amalgamated terranes in the Sorong Fault Zone include the East Sulawesi terrane, the Obi terrane and the Bacan terrane. These terranes are composed of rocks of various affinities and have been assembled either by the left-lateral movement of the Sorong Fault or collision between terranes. The East Sulawesi terrane is a product of collision and subsequent obduction of ophiolitic rocks (Silver et ah 1983). The Bacan terrane formed chiefly by collision of the northern margin of the Australian continent with the Philippine Sea Plate in the Early Miocene (Malaiholo 1993) and was translated to its present position by the left-lateral movement of the Sorong Fault. The Obi terrane may have resulted from collision between the Philippine Sea Plate and the Australian continent and have been translated towards west-northwest by a strand of the Sorong Fault (Hall et al. 1987, Hutchison 1989).

69 4.6.1 East Sulawesi Terrane

The East Sulawesi terrane includes the East and Southeast arms of Sulawesi. The western side of the province is bounded by a zone of thrust and fold belts, separating the province from the Central Sulawesi Metamorphic belt. To the east, the northern part of the province is separated from the Banggai-Sula Platform by the Batui Thrust and the south and southeastern parts are bounded by the Lawanopo Fault and the Tolo Thrust, isolating the province from the North Banda Sea terrane. To the north, the Gorontalo Basin marks the northern edge of the East Sulawesi terrane.

The East Sulawesi terrane is composed predominantly of ophiolitic rocks which are dismembered and tectonized (Silver et al 1983). In the East Arm, the ophiolite contains a complete, although tectonized, sequence of ultramafic and mafic rocks, dykes, basalts, and pelagic sedimentary rocks. In the Southeast Arm, the ophiolite is represented mainly by harzburgite and serpentinized harzburgite. Mesozoic sedimentary rocks occur extensively on both East and Southeast Arms and mélange belts are widespread throughout the Southeast Arm but their occurrence on the East Arm has not been reported (Silver et al 1983).

4.6.2 Obi Terrane

The Obi terrane occupies an area which includes the islands of Obi, Tapas, Bisa, Obi Latu and other small islands adjacent to Obi (Fig. 4.13). The terrane is composed predominantly of ophiolitic rocks of Philippine Sea origin and sedimentary rocks with Australian continental margin affinities. The ophiolites of Obi in general are equivalent to those found in East Halmahera. These rocks form the basement of central Obi and possibly underlie the entire area of north Obi which in turn is overlain by volcaniclastic units and a sedimentary sequence derived from the northern margin of the Australian continent (Hall et al 1987).

The ophiolite of Obi comprises a complete ophiolitic sequence, from ultramafic rocks through cumulates and microgabbros to volcanic rocks. In the western part of the island, extensive latérisation and soft rounded topography indicate the predominance of

70 ultramafic rocks and most coastal exposures show serpentinized harzburgite, locally with serpentinized orthopyroxene-rich layers. The ophiolite in turn is intruded by diorites (Hall et al. 1987). In south Obi, a few kilometres from the coast, there is a massive exposure, locally sheared serpentinized harzburgite. Further inland exposures of dolerites which appear to be part of a sheeted dyke complex may be encountered but are deeply weathered. Basaltic lavas and pillow lavas are found further inland from the sheeted dyke complex. The attitude of the ophiolitic sequence is undetermined but the pillows appear to be in a vertical orientation.

The sedimentary rocks of Obi may be categorised into two groups, these being the volcaniclastic sediments associated with arc activity of the Philippine Sea plate and sedimentary rocks with Australian continental margin affinities. The volcaniclastic sedimentary rocks which are exposed in the northern part of Obi and which are associated with arc activity of the Philippine Sea plate are similar in characteristics and attitude to equivalent rocks found in East Halmahera, supporting a relationship between the Obi ophiolites and those of the East Halmahera-Waigeo terrane.

4.6.3 Bacan Terrane

The Bacan terrane includes Bacan island and smaller surrounding islands including the Saleh Isles, Nusa Babi, Ruta, Kasiruta, Mandioli and Muari (Fig. 4.14). The Molucca-Sorong Fault marks the southern boundary and separates the Bacan terrane from the Obi terrane. On the west, the West Halmahera Thrust form the western boundary isolating the Bacan terrane from the Molucca Sea Collision Zone (Fig. 4.1).

The Bacan terrane is composed of metamorphic rocks of continental and oceanic suites (Malaiholo 1993), represented by the Sibela Metamorphic Complex. The continental metamorphic suite includes schists, gneisses and continental phyllites which, on the basis of whole-rock chemical analyses (Malaiholo 1993), are similar in character to rocks from the northern margin of the Australian continent. The oceanic metamorphic suite is composed of ophiolitic rocks, most of which are of lower crustal origin with minor volcanic components (Fig. 4.14). Petrography and whole-rock chemical analysis reveal an arc-related environment (Malaiholo 1993).

71 V V V|V|V V V V W '/V V V V V V 7 \/W V , y . V ^ V vvvvvvvvvvvvvvvvvvv •• • V •• ■ V •• ■ -'A • > • k ' X I ■ -c ' V V/V VVVVVVVVVVVVVVVVVVVVV V ■ ■ f r ; T f r ' ;V.' ' V ' -V a ' 9 , VV^VVVVVVVVV TOaiAN / vvvvvvv\ vvv'fvvvvvvvyv isla n d s v v v v v v v ' vvvyvv NUnt-Urat Qf V V V V vvv.vvvvvvvvv \L _ J y v V A /& /k /, A A / ^ A A a > a^ a a a a a a a a a a a

A A A A A J / V V VfV V A A A A, J, Makasar ^Thrust , KEPALA BURUNG Strait V V V V * * SALAWATI -j . ' V V V VC A A A A #\ .. 4^ f + + t + + + + + * + V V vj V V V \ t \ )A A A^/WAA'*/^ a A a A ^ + + + + + + +Vy + + + + + + ✓ v v w v v v \ ^ A A A A 2°S V V v\v V V V 'sal»»»*’' ii>' r/^OQ, V V V /^ V V V V V V ^"^ITh 0ur^ !■♦♦♦♦ ♦ ♦ ♦ 4. 4. 44. 4.V.. V V V Y V V V V V V V V / V V V v k S U L A W E S I v v *. + * *. * Continental Shelf % % % % % % vvvvvyvvvvvvvvv V V V vvv vvvvvvvvvv / V vvvvvvvvvvv Worth^anda Sea :■ rp V '. Buru-Seram On/n Peninsula ■ vv(v^vvvvvvvvvvv Ivvvvvvvvv ' Micrcheontlnent - vvr^vvvvvvvvvv IRIAN JAYA \v vvvvvvvvvv’ [vvvvvvvvvvv V V %v/yuiFSs.v V V V V V vvvvvvyvvvvvv , kumawa V V V V V V V V V V V y v V Peninsula- 4°S V V V V V V V y V V V V vf^v V South Banda S«à- V V V V V V V V)V V /'J .' V ' ' i'_ I'- ■; c I'- o' C%' f118°E V V V V V V V y V V, , li 73p'E:,/XÔ 132° , 134°E^

✓ VVVVVVVVV' VVVVVVVVVV /VVVVVVVVV' liVesf Sulawesi Volcanic Province Oceanic crust of North Banda Sea East Halmahera-Waigeo Terrane vvvvvvvvvv and South Banda Sea basins j g j K> I l l ' 11 Central Sulawesi Metamorphic Beit W m II) North Buru-Saiawati Tectonised Zone Obi Ophilitic Terrane

\\\\\\\\\\ East Sulawesi Ophiolite Terrane Ambon Volcanics \\\\\\\\\\ Bacan Continental vvv\.vvvv\.^ Metamorphic Terrane

Continental rocks derived from the Northern Margin of Australia Seram Thrust Beit Thrust

AAAAAAAAAA Surface trace of Molucca Sea Tectonic Mélange AAAAAAAAAA West Halmahera-Tamrau AAAAAAAAAA subduction AAAAAAAAAA Volcanic Terrane Strike slip fault 0 Kilometres 200 showing sense of movement

Figure 4.1 Sorong Fault Zone, showing the principal tectonic features and distribution of terranes of various origin. Oceanic terrane are thought to have originated from the Indian Ocean and the Philippine Sea plates. Terranes with continental affinities were derived chiefly from the Australian continental mass. Arc terranes in the fault zone mainly formed by collision between the Australian continent and the Philippine Sea Plate. The amalgamated terranes formed by collision between terranes of various affminities (sources: Hamilton 1979, Silver et al. 1983, Pigram and Davies 1987, Letouzey et al. 1983, Réhault et al. 1991, Charlton 1994). 5 a @ # s

▲ A KALIMANTAN h a l m a h e r a :-" + IRIAN JAYA

BANGGAI-SULA SULAWESI SERAM BURU

JAVA SEA

-f ARAFURA SEA + : JAVA ^ 4- 4- 4- 4- -l- 4- 4- 4-4-4-4-4- + 4- +

INDIAN OCEAN

125°E

Figure 4.2 Eastern Indonesian Region, showing a tectonic model which accommodates sliver kinematics leading to the complex terrane distribution in the Sorong Fault Zone and the surrounding areas (simplified from Charlton 1986). Asian Crust. Asia-Australia collision zone. + Australian crust. Early Neogene volcanic arc local seafloor spreading associated with transtension. current forearc. | subduction zone. current volcanic arc. Indian Ocean crust. crust. HALMAHERA Gorontalo GULF Basin OF ^South Halm ahara TOMINI B asin

BACAN? KEPALA BURUNG EAST MOLLUCA ARM 2000

TALIABU Salawati IRIAN JAYA Basin Tomori Basin ISOOL SULAWESI 5000 n SULABESI 3000 GULF GULF F TOLO OF NORTH BANDA '-J BONE SERAM SOUTHEAST BASIN ARM BURU Bone Basin ra

K ilo m o tr e s 120 E 134‘E

Figure 4.3 Bathymetry of the Sorong Fault Zone and the surrounding region. The 200 and 1000 m contour lines are useful marks which may indicate terrane boundaries (simplified from Hamilton 1979). AAISOOL.SOBO.C Strt.4^SOWOWO fAULT

NORTH /voftrw WOflTH SU LA’SORONG WSOOL.SORONO TECTONISED ZONE FAULT

SOUTH NORTH NORTH SOUTH NORTH m is c Z l S o r o n g SERAM’SALAWATI HALMAHERA S e# Lev#/ *VESr MISOOL FAULT TECTONISED ZONE LA

f4SrSUL4

0 Kilométré» 25

Figure 4.4 Interpreted seismic profiles, showing the approximate locations the various strands of the Sorong Fault (redrawn and modified from Letouzey et al. 1983). SE Distance (Km)

? 2000 È k Sula Thrust î X

4000- Llne: ES-S2

SE NW Distance (Km) 40

Su/a Thrust

< 1 On

4000 Line; ES-S4

^ ES-S4

OULF i'

Figure 4.5 Interpreted seismic profiles north of the Sula-Islands region, showing the inferred location of the Sula Thrust (simplified and modified from Silver et al. 1983). WAGEO HALMAHERA Gêbê Netoni Esst Halmahera-Waigeo Terrane Terrane V/vVKoof Fault /A V BATANTA ■^^Sgrong ^u ltj^ —

Arfak Molucca-Sorong Fault RAJA AMPAT Kemum Terrane — —» — —« SALAWAV

M is œ c

Misool Bintuni Bay — Bintuni / / / / / ■/'">< Basin — V-~— SERAM OnIn Peninsula Langguru Terranes of Kepala Burung Irian Jaya — ~ Tarrana — < / ^ Metamorphle baaamant reeks [2—2 —] MIoeana ana younger sedlmtnts Misool Tarrana (Palaaoiolc)

UpperEoeana-MlrldiaMiocene f - — Metamorphic baMmant roeka Volcanics L ~ _ ~ J Kemum and Langguru =" (Palaeotolc) Crataceoue Ultramallc complex Fault Kumawa pra-Lala Crataceoue Peninsula Mena area volcanica Surtaca trace P » I? Lata Parmlan-Early Triaaalc otaubducSon I " " I granltolda ARAFURA SEA Source: Pigram and Davies 1987 I 132 E I 134'E

Figure 4.6 Terrane distribution in the Kepala Burung area Irian Jaya (redrawn and modified from Pigram and Davies 1987). CELEBES-SANGIHE HALMAHERA PHILIPPINE VOLCANOES^F MOLUCCA^ VOLCANOES y TRENCH

'-J 00 UNE OF SECTION

BASIN

. SANQIHE PACIFIC

, ^ JAY^ BANDA S£A iciiii

Figure 4.7 Lithospheric section beneath the Molucca Sea Collision Zone, showing earthquake foci which delineate the two Benioff zones dipping in opposite directions (source Cardwell et a i 1980). - o b served - com p u ted

0 mGal

Molucca Tataud-Mayu 100 mwge 150

20 - mi#### 30 -

~ Sangihe Arc Halmahera Arc / -200 ^ 0 200 . y 400

VO

* 0.20 *OJtQ

*ao5 *0J>5

• = Earthquake foci

Figure 4.8 Crustal and lithospheric gravity model of the Molucca Sea Collision Zone (after McCaffrey and Silver 1980). Quaternary MOROTAI □Alluvium and Limestone Quaternary-Recent Volcanic Rocks PUo-Pleistocene Volcanic Rocks Weda Group

Loku Formation

Wocene Limestones Early-Mid Miocene HALMAHERA Sedimentary Rocks Tawali Formation Oha Formation Volcanic Rocks Ophiolitic Basement Complex Continental Metamorphic Rocks

TERNATE

TIDORE

Major Thrust Major Fault A Volcano

W eda Bay

KASIRUTA

BACAN

127^E 128°E 129°E

Figure 4.9 Simplified geological map of Halmahera and the surrounding islands (after Hall et al. 1992).

80 WAIGEO

+ 0‘ Teluk Fofak Kawe Kobare Island

Tanjung Bomos

Teluk Ayul

Tanjung Monfafa

00 %

GAM ®SAONEK 0‘>30'S 4- |~ - 1 Quaternary (alluvium and reef limestone)

# -# Waigeo Formotion — 0 -, Anticline fold axes

lllllllllllllllll Mayalibit Formation ' Syncline fold axes W ivrl Rumoi Formation " Hoif-syncline, with Lomlom Formation flot-ramp geometry Thrust Ijniiiiiij T anjung B om as form ation " Normal fault Ophiolite complex U ltrobasic " Strike-slip fault 20 km

Figure 4.10 The geological map of Waigeo Island (simplified from Hall et al. 1992). GULF Recent Alluvial Early Jurassic sandstones and OF deposits conglomerates (Bobong Fm.) GORONTALO East Arm Quaternary carbonates Cretaceous Ophiolites (Peleng/Luwuk Fm.) Batui Pllo-Plelstocene Permo-Trlassic volcanics Thrust Celebes Molasse

Tertiary carbonates Permo-Trlassic granites (Salodlk/Pancoran Fm.) (Banggai Islands) Peleng MOLUCCA SEA Late Cretaceous-Early Tertiary Palaeozoic basement rocks carbonates (Tanamu Fm.)

Late Jurasslc-Early Cretaceous \^Fault Thrust shales (Buya Fm.) Banggai

Mangole

00 to Taliabu GULF Salue OF Group Sulabesi TOLO NORTH BANDA SEA

\12T£ 124°E 125°E 126rE

N MOLUCCA .Ititn ta SEA 1

SERAM SEA SULAWEi 0 100 Seram T Buru Kilometres ' BANDA SEr

Figure 4.11 Simplified geological map of the Banggai-Sula region (after Garrard et al. 1988). Kilometres 100 SERAM SEA

Seram Island 3?S

Kelang Kayell Bay PIru Bay Manlpa

Haruku Buru 00 Island Ambon w BANDA 4°S SEA 128TE 131°E Thrust Quaternary sediments MOLUCCA Ultramafic rocks SEA

Ktptim Buninç Fault IRIAN JAY A Neogene Seram sequences Sedimentary sequences of SERAM SEA Australian margin (Mesozoic) SULAWEi

Bow Pliocene Volcanics (Ambonites) Granitic and Metamorphic fS basement rocks (Palaeozoic)

Figure 4.12 Simplified geological map of the Buru-Seram Microcontinent (after Tjokrosapoetro and Budhitrisna 1982). KEY:

Alluvium QUATERNARY Reef Limestone 1

South Obi Fm. Obi Majora Anggal Fm. Obilatu NEOGENE Wol Fm.

Fluk Fm.

ri5's 00 OLIGOCENE Anggal River Fm.

Leleobasso Fm. MESOZOIC Ophiolitic Basement Complex

MESOZOIC ///j Gomumu and Sollgl /////] / / / / ' Formations — ^ Continental PALAEOZOIC Metamorphlcs Gomumu

127°30'E 128°00'E

Figure 4.13 Geological map of the Obi Island and surrounding areas ( simplified from Hall et al. 1992, Agustiyanto 1995). Muari 127’30'E O’IS'S

Kasiruta SaIeh Isles

% 128‘00‘E 0‘30‘S

KEY: I l Quaternary Screo

LïÿiïJ Quaternary Alluvium

M W ':I Quaternary Delta LAo o Quaternary Limestone Quaternary Volcanic Kaputuaan Formation Mandioll Mandioll Memtrer BM m Kaputuaan Formation Padtak Memtyer Kaputuaan Formation Goro-goro Memtoer ifMüii Amaaing Formation

Ruta Formation

South Bacan Formation I Nusa BabI Intrusive Tawall Formation

Bacan Formation Saieh Metamorphic Complex SItwIa Metamorphic Complex Qphlolltic Affinity Sibela Metamorphic Complex Continental Affinity

Figure 4.14 Simplified geological map of Bacan Island and surrounding areas (after Malaiholo 1993). Chapter 5 SIDESCAN SONAR, SEISMIC IMAGES AND SEISMICITY

This chapter discusses the response of some sectors within the Sorong Fault Zone as expressed by GLORIA sidescan sonar imagery and reflection seismic sections as well as the seismicity. It attempts to correlate the signatures, if any, identified using data of these types with the characteristics of a strike slip regime. The GLORIA sidescan sonar imagery was obtained firom the RRS Charles Darwin Cruise CD30 (Milsom pers. comm. 1995), the reflection seismic profile was available from a commercial survey and the seismicity data were based on the world-wide seismological network database 1986, obtained fi-om the National Geophysical and Solar Terrestrial Data Center, NOAA, Boulder, Colorado, USA.

5.1 Sidescan Sonar

This section describes the GLORIA sidescan sonar images acquired in parts of the Sorong Fault Zone, highlights some technical aspects of the sidescan sonar system and explains some fundamentals of the interpretation criteria applied to the images in the region.

During the course of the 1988 RRS Charles Darwin Cruise CD30 in Eastern Indonesia, GLORIA long range sidescan sonar imagery was obtained over a significant part of the sea covered sectors of the Sorong Fault Zone (Fig. 5.1). The primary target of the cruise was not the Sorong Fault Zone but it was crossed on passage legs between the target areas west of Halmahera and those in southern Banda Arc. Images from the two passage legs involved could be assembled into a mosaic covering a marine area of about 33,000 km^.

The principle of sidescan sonar imaging of the seafloor is to emit pulses of a soundwave energy in a narrow beam at right angles to the track of the vessel (Sommers et al. 1978). These pulses are reflected by seafloor and recorded to produce acoustic images which are built up by successive scans as the vessel moves ahead. The GLORIA Mark 2 sidescan sonar system deployed during the RRS Charles Darwin Cruise CD30 is a dual scan sonar which is encapsulated in a towed vehicle capable of sustaining a maximum tow speed of 10 knots (1 knot = 1.85 km.h'^). The towed vehicle measures

86 7.75 m by 0.66 m and weighs 2.04 tonnes in the air. The acoustic transducer consists of 2 rows of 30 elements on each side and operates at 6.2 to 6.8 Khz with a 100 Hz pulse swept frequency. The transducer active length is 5.33 m, with a horizontal angular beam width of 30° at a fixed inclination of 20° below horizontal. The size of the area covered depends on the water depth, with a maximum swathe width in water more than 3000 m deep of about 40 km. There is also a shadow zone a few kilometres wide immediately beneath the vessel from which no data can be recorded.

The interpretation of the GLORIA sidescan images was made on the basis of distinguishing patterns and contrasts in reflectivity of sea-bottom features, as portrayed by the backscattered soundwave energy which is recaptured by the receiving unit of the sidescan sonar system. Recognizable patterns which may represent sea-bottom geology include circular, elliptical and linear features. The intensity of the backscattered energy, which is determined by the reflectivity, is represented by greyscale which may be quantified in a sequential order from the darkest to the brightest images i.e. very dark, dark, moderate or fair, bright and very bright, corresponding to very low, low, moderate or medium, high and very high reflectivity. Quantifying this scale more accurately in numeric form would be preferable but for the purpose of the discussion in the present study, the scheme outlined above was considered adequate. Dark images indicate strong absorption of soundwave energy by the sea-bottom, leaving a small fraction of reflected energy to be recaptured by the GLORIA system. This is characteristic of thick layers of uncompacted sediments overlying the seabed and of smooth seafloor. Bright images suggest strong scattering of the soundwave energy from the seafloor and may be identified as indicating rough sea-bottom surfaces, which may possibly be due to exposed basement rocks being scoured by strong under-water currents, especially in narrow channels separating open , but may also indicate coarse sand cover of the seafloor. The interpretation of images with intermediate levels of reflectivity poses difficulties in that it combines parts of the two extreme cases outlined above, each part with its own level of reflectivity.

In making the interpretation, line drawings were made to define the boundaries or lineations of the contrasting sea-bottom features. Visible lineations which may result from tectonic or lithological features were traced and drawn for interpretation (Fig. 5.2). The interpretation is made more difficult by the presence of the shadow zone immediately beneath the vessel and also by uncertainty as to the range (which is very variable) at which usable data are no longer being acquired. The range limit is not

87 strongly indicated on the imagery. Multiple paths can cause double imaging of steep slopes near the range limit (Milsom pers. comm. 1995).

The areal coverage of the GLORIA sidescan sonar imagery in parts of the study area forms a four-armed pattern with its central part occupying the region midway between Buru, Obi and Mangole (Fig. 5.1). The central region lies in the western part of the deep basin of the Seram Sea where bathymetric depth reach to more than 5000 m. The eastern arm of the coverage extends as as the region southeast of Obi at about 128.6°E; 1.75°S. The northern arm extends north between Obi and Mangole islands, forming a curving path west of Obi at about 126.7°E; 1.5°S. It continues northeastwards as far north as the region northwest of Tapas Island, about 25 km northwest of Obi Island, at approximately 127.45°E; 0.85°S. The southwestern arm extends southwest past Sulabesi and to the west of Buru and continues as far as southwest as the deep basin of the North Banda Sea where bathymetric depths are in excess of 5000 m. The sidescan sonar imagery extends further southwest into an area beyond the scope of the present study. The southeastern arm extends southeast through the relatively narrow seaway which separates Buru and Seram and curves southwest at about 127.8°E; 3.7°S (southwest of Ambon Island). From there the cruise continued southwest into a region which is not covered by the present study.

5.1.1 Eastern arm GLORIA coverage

In the eastern arm, the GLORIA sidescan sonar imagery shows a wide range of reflectivity, displaying dark, moderate, bright and very bright images and exhibits a number of prominent features which can readily be identified (Fig. 5.1). These include firstly, an E-W oriented elliptical pattern characterised by moderate brightness with a size of about 5 by 10 km, situated at about 128.6°E; 1.75°S. Secondly, a strong linear feature characterised by bright to very bright images, about 5 km in width, extending across the entire northern part of the region from about 127.8°E; 1.9°S to 128.45°E; 1.85°S. Third, linear pattern oriented NE-SW situated in the southern part of the region, extending from about 127.9°E; 2.2°S to 128.2°E; 2.1°S but possibly continuing east-northeast to about 128.4°E; 1.9°S. Fourth, an elliptical pattern characterised by moderate brightness with a NW-SE orientation, about 20 by 10 km in size, occupying part of the region with its centre situated at about 128.45°E; 1.9°S. Fifth, a truncated elliptical pattern, shown by its northern half with the long axis oriented NW-SE and about 25 km wide, centred at about 127.7°E; 2.2°S. It is characterised by low to

88 moderate level of reflectivity, bounded in the north, west and south by patches of bright images and darker in the east which define its geometry. Sixth, a terracing patterns characterised by wide a range of levels of reflectivity, encompasses almost the entire southwestern part of the region as well as extends into the eastern part of the central region, from about 127.55°E; 2.25°S to 127.25°E; 2.4°S.

The E-W oriented elliptical pattern with a moderate brightness in the extreme northeast of the region is interpreted as a north-facing fault scarp with the down-thrown block situated to the north. The E-W oriented strip characterised by dark images in the centre, about 8 km long and 1 km wide, is interpreted as due to sediments which are probably uncompacted and soft. Flow patterns may be identified from the extreme east of the area, depositing sediments at the base of the slope in the western part of the area. This E-W oriented lineation may form part of a set of lineations approximately in the same orientation which are possibly associated with a strand of the Sorong Fault. By identifying the geographic location of these lineations and comparing them with the tectonic map of the region and surrounds {cf. Fig. 1.2 and Fig. 1.4) and referring to the discussion in Section 4.2 (Strands of the Sorong Fault), these lineations were interpreted as the seafloor expression of the North Sula-Sorong Fault. The western continuation of these lineations can also be identified on the sidescan sonar imagery in the northern arm of the GLORIA coverage although they are not as clear as in the eastern arm.

The prominent linear feature which is oriented E-W and characterised by bright to very bright tonal images, is interpreted as representing the seafloor expression of a strand of the Sorong Fault. It extends for almost the entire central northern part of the region at the latitude of about 1.9°S. The bright to very bright images were interpreted as indicating exposed rough surfaces of basement rocks with thin or no sediment cover, suggesting recent tectonic movements but may simply be an expression of rough seafloor being scoured by strong under-water currents. By considering the contrasting tonal characteristics of the juxtaposing images to the north, this distinct E-W linear feature with bright to very bright images is probably a genuine representation of uplifted blocks which resulted from transpressional kinematics along a strike slip fault. The contrasting dark images to the south were interpreted as representing the lower blocks where sediments may have accumulated, giving dark tonal images in the central southern part of the region. By identifying the geographic coordinates, comparing the feature with the tectonic elements in the region and referring to fault strands discussed in Section 4.2, this E-W linear feature has been interpreted as forming part of the South

89 Sula-Sorong Fault {cf. Fig. 1.2 and Fig. 4.1). The western continuation of this fault can be traced on the sidescan sonar imagery in the northern arm although it is not as distinct as in the eastern arm.

The linear pattern oriented NE-SW in the central southern part of the region is interpreted as a thrust front, probably part of the western continuation of the Seram Thrust Belt {of Fig. 4.1). Shorter linear features of similar orientation to the west may indicate a series of NW-directed thrusts. The generally rough surfaces with moderate, dark and very dark images may be interpreted as representing rapid sedimentation in a tectonically active region.

The NW-SE oriented elliptical pattern with a moderate brightness with a size of about 20 by 10 km and situated close to the extreme east of the region is interpreted as marking a SW facing fault scarp. It may form a series of block faults with the down- stepping direction towards the southwest. The down-stepping blocks which face southwest and the associated pattern of sea-bottom channels may be traced towards an elliptical pattern characterised by dark images in the centre, situated at about 128.1°E; 2.1°S, where sediments likely to have accumulated. The dark images of about 5 km long in the centre of the elliptical pattern may represent sediments, possibly soft and deposited in a localised and small depression on the seafloor.

The NW-SE striking truncated elliptical pattern which is situated close to the southwest end of the region covered by the eastern arm is interpreted as a down-thrown block probably associated with faulting mechanism which resulted from complex strike slip kinematics in the region. The down-thrown block appears to dip SSE but moderate to bright patches of images on the periphery of the elliptical pattern may indicate some degree of NE-dipping component as well. Rough seafloor surfaces with bright tonal images in the area may suggest exposed basement on the fault scarp and the smooth seabottom surface with dark to very dark images is interpreted as representing a local depression in the seafloor covered by uncompacted and soft sediments.

The terrace pattern in the extreme southwest of the region is characterised by a wide range of levels of reflectivity and is interpreted as the seafloor expression of extensional faulting with the down-stepping blocks directed towards the southwest. It extends for about 60 km from the southwest part of the eastern arm, where the swathe width narrows to about 20 km, into the southeastern part of the central region. It may include the entire central region as indicated by NW-SE lineations which may represent

90 fault scarps which face southwest. This may be the transtensional region of a strike slip system, possibly one which resulted from the interaction between the North Sula- Sorong and the South Sula-Sorong faults {cf. Fig. 4.1). Flow patterns on the terraced seafloor may readily be identified, along with localised depression where sediments are likely to have accumulated in areas indicated by dark tonal images. The generally SW- directed flow pattern agrees with the orientation of the terraced seafloor which is also down-stepping towards the southwest. Bright images which are oriented NW-SE at about 127.25°E; 2.4°S are interpreted as marking fault scarps, showing the imbrication of possibly collapsed blocks of the rockwall.

5.1.2 Central region GLORIA coverage

The sidescan sonar imagery in the central region is characterised by the whole spectrum of reflectivity, with brightness levels which extend from very dark to very bright tonal images. The region shows a generally rough seafloor with readily identifiable lineations oriented NW-SE to NNW-SSE, extending almost the entire breadth of the assembled swathe covering the region. These lineations are interpreted as representing fault scarps which resulted from extensional faulting in a transtensional zone of a strike slip system which in turn, resulted from the interaction between the North Sula-Sorong and the South Sula-Sorong faults {of discussion on the eastern arm of the GLORIA imagery above). Other prominent features which may be identified include an elliptical pattern of about 50 by 20 km characterised by mostly dark images occupying the northwestern part of the region with its centre situated at about 126.6°E; 2.3°S, a smaller elliptical pattern characterised by moderate to bright images, about 30 by 10 km, with its centre situated at approximately 126.85°E; 2.45°S, and a linear feature oriented E-W, about 8 km wide, extending over the entire swathe in the northeastern part of the region.

The elliptical pattern in the northwestern part of the region is interpreted as representing a down-thrown block of probably an extensional faulting system with its escarpment facing WSW and striking NNW-SSE. Fragments of collapsed blocks of rocks accumulated at the base of seabottom cliff at about 126.7°E; 2.4°S. The generally dark images suggest extensive sediment cover but patches of images with a moderate level of brightness can be identified and may be representations of exposed basement rocks.

91 The elliptical pattern which is characterised by moderate to very bright images in the central part of the region is interpreted as a seafloor ramp which dips SSE. Short, E- W oriented lineations in the north and south periphery of the elliptical pattern are interpreted as thrust fronts which may be the western continuation of the Seram Thrust Belt {cf. Fig. 4.1). The southern part of the ellipse shows flow patterns directed towards south and southwest, transporting sediments into the deepest part of the western sector of the deep basin of the Seram Sea. Dark images which are characterised by fairly rough seafloor may suggest that deposition of sediments has taken place and was probably taking place whilst the basement rocks experienced tectonic movements. Bright to very bright images in the southwestern part of the region are interpreted as marking the southern slope of the basin.

The linear feature which is oriented E-W and situated in the northeastern part of the region is interpreted as the western continuation of the South Sula-Sorong Fault which can be identified more clearly on the sidescan sonar imagery in the eastern arm of the GLORIA survey coverage (Fig. 5.1). This feature can be recognised to extend for about 40 km with a width of approximately 6 km. It is characterised generally by moderate to bright tonal images with some degree of surface roughness on the seafloor. This may suggest the deposition of sediments in a tectonically active region.

5.1.3 Northern arm GLORIA coverage

The GLORIA sidescan sonar imagery in the northern arm generally shows moderate to very bright images, exhibiting linear features and some degree of surface roughness. The northern half of the region from about 126.7°E; 1.5°S to the northern end of the swathe is characterised by moderate to very bright images with some lineations which are oriented E-W and ESE-WNW. The bright images close to and in the eastern part of the swathe may be interpreted as representing a very steep bathymetric slope from the western sector of the South to the deeper basin of the Molucca Sea. Three linear features which are oriented E-W to ESE-WNW situated at approximately 127°E; 1.1°S are interpreted as thrust fronts, which probably are the southern part of the West Halmahera Thrust. Moderate to dark images with some degree of surface roughness may suggest deposition of sediments which have taken place while the basement experienced some degree of tectonic activity.

92 The southern half of the northern arm is characterised by narrowing of the swathe, indicating shallowing of the seafloor. Bright tonal images which characterise almost the entire region are interpreted as representing the rough surface of the seafloor which is being scoured by strong under-water currents in a relatively narrow sea passage which connects the Molucca and Seram seas. The slightly curving NW-SE lineation at about 126.7°E; 1.65°S is interpreted as the western continuation of the North Sula-Sorong Fault.

5.1.4 Southwestern arm GLORIA coverage

The sidescan sonar imagery in the southwestern arm shows moderate to bright images, exhibiting linear features and some degree of surface roughness. These are mostly found in the north and to the lesser extent in the central part and south of the region where the seafloor shows smoother surfaces. The western part of the swathe in the north shows a prominent N-S linear feature southeast of Sulabesi and a southwest- facing terrace pattern situated south-southwest of Sulabesi. The N-S linear feature about 5 km wide with its southern end situated at approximately 126.15°E; 2.6°S is interpreted as representing a zone of strike slip faulting which, in terms of the fault strands discussed in Section 4.2, would be a transfer zone which connects the South Sula-Sorong Fault east of Sulabesi and the South Sula-Sorong Fault west of Sulabesi. This zone has also caused some degree of offset to the fault with the entire block of Sulabesi represents the transfer zone. The terrace patterns on the western part of the swathe exhibit flow configurations with the down stream area situated in the southwestern part of the region. They extend as far southwest as the deep basin of the North Banda Sea at about 125.55°E; 2.6°S.

In the extreme north of the region at about 126.3°E; 2.6°S the sidescan sonar imagery shows a moderate brightness with a relatively smooth seafloor. This may be interpreted as a deep basin in a relatively quite region where the rate of deposition of sediments has been slow, i.e. a starved basin. The weak NW-SE lineation at about 126.3°E; 2.7°S and another weak WNW-ESE lineation at about 126.25°E; 2.7°S may be interpreted as localised depression, possibly graben structures.

The narrowing width of the swathe in the central part of the region (which encompasses an area of about 30 by 50 km with its centre at about 125.8°E; 3.1°S)

93 indicates shallowing of the seafloor and is interpreted as a bathymetric ridge which probably forms the boundary between the Seram Sea and the North Banda Basin.

The rest of the southern part of the region is in general characterised by moderate to dark images, showing mostly smooth seafloor. Images with moderate reflectivity are interpreted as representing exposed basement rocks, probably covered by thin layer of sediments and the darker images which show smooth seafloor are interpreted as representing deposition of sediments in a tectonically tranquil region. The NW-SE oriented lineations which accompany the narrowing of the swathe close to the extreme southwest of the region, suggest a slightly elevated seafloor, which is probably the seabottom expression of the West Bum Fracture Zone {cf. Fig. 1.2 and Fig. 4.1).

5.1.5 Southeastern arm GLORIA coverage

The sidescan sonar imagery in the southeastern arm shows the whole spectrum of reflectivity, ranging from very dark-moderate level in the south, moderate-bright in the north to bright-very bright level in the central part of the region. The generally moderate-bright images which show some degree of surface smoothness in the northern part of the region are interpreted as representing accumulation of sediments, probably fairly thick with the topmost layer possibly soft and uncompacted. The smoothness of the seafloor suggests that sedimentation might have been occurring in a relatively tectonically quiet, small isolated area. An E-W oriented lineation characterised by bright images at about 127.3°E; 2.9°S is interpreted as a north-facing escarpment probably associated with extensional faulting. Rough surfaces with bright images southwest of this lineation are interpreted as representing a steep bathymetric slope in this part of the fault scarp.

Bright-very bright images which are characterised by relatively smooth seafloor in the northern part of the central area are interpreted as representing sediments fans of probably sandy nature. Distinct flow patterns with an E-W to NE-SW orientation can be identified west of the fan at about 127.4°E; 3.3°S. The flow configuration is probably the offshore continuation of the Wa Apu (Apu River) onshore Bum, which flows NE into Kayeli Bay.

The prominent N-S oriented feature which shows bright images and exhibits rough seabottom is interpreted as indicating the steep bathymetric slope of the eastern

94 Bum shelf margin. Rough and granular texture shown by the seafloor at about 127.45°E; 3.55°S has been interpreted as representing fragments of collapsed rocks which probably resulted from erosion of the steep slope of the east shelf margin of Bum Island. The linear feature which extends NW-SE from about 127.5°E; 3.3°S to 127.6°E; 3.45°S indicate multiple reflection generated by the western shelf margin of Island.

The most prominent feature in the southern part of the region is an elliptical pattern which is oriented NW-SE and is centred at approximately 127.6°E; 3.7°S. The NW-SE parallel lineations are interpreted as multiple scattering patterns generated possibly by an under-water volcanic cone which is probably part of the volcanic chain offshore west of Ambon and Seram.

5.2 Seismic images

This section discusses a seismic profile (Line QS-1) which is oriented NNE- SSW and extends for approximately 150 km from the shelf region northwest of Taliabu to the southern part of the Gorontalo Basin (Fig. 5.3). The profile shows some important features of the North Sula-Sorong Fault Zone, the strand of the Sorong Fault Zone in this area. Strike slip movements along the fault may have, at present, slowed or ceased because the Banggai-Sula Platform has collided with the East Sulawesi. Thmst tectonics may now predominate in this part of the region (Letouzey et al. 1983) but direct evidence of thmsting could not be identified on the seismic section discussed here.

In the discussion which follows, the seismic profile has been divided into four segments on the basis of recognised seabottom morphology which is, in general, an expression of the underlying geology. Segment 1 covers the southernmost 30 km of the profile and shows prominent gently northwards-dipping sedimentary layers which conformably overly the acoustic basement. Immediately to the north. Segment 2 which extends for approximately 40 km, is occupied by a distinct bathymetric depression characterised by strong diffraction patterns which may indicate the transtensional zone of the North Sula-Sorong Fault, the strand of the Sorong Fault Zone in this part of the region {cf. Fig. 1.2). Segment 3 comprises an asymmetric bathymetric ridge extending for approximately 60 km. The northern half of the ridge is overlain in places by significant thickness of sediments. In Segment 4, the northernmost 40 km of the profile,

95 a sequence of relatively undisturbed sedimentary strata (up to about 1.5 s TWT thick) is underlain by acoustic basement at depth of approximately 6 s TWT.

Analysis to obtain density values which were derived from velocity of seismic wave were also made following the method suggested by Nafe and Drake (1957). These results were used as comparison to the density values assigned in the gravity modelling work discussed in Chapter 6 of this thesis. Results of the analysis are tabulated in Appendix F (Table F.l).

5.2.1 Seismic images Segment 1

The seismic images in Segment 1 (Fig. 5.4) are interpreted as predominantly characterised by the development of a shelf carbonate platform. Carbonate build-up typical of a shelf margin setting (Sun and Esteban 1994) occupy the topmost 100 to 200 ms TWT below seafloor. They extend as far north as the shelf slope and include a mound structure at about 2 s TWT, 27 km from the south end of the segment. The drowning of this carbonate platform probably resulted from the sinking of the Molucca Sea lithospheric plate. A prominent reflector (A-B) dips gently northwards from a depth of about 400 ms at the southern end of the segment and can be followed as an almost continuous reflector to a depth of approximately 1.2 s TWT before distortion of the images occurs. The cause of the distortion is probably velocity pull-up, under the positive bathymetric feature (possibly carbonate build-up) at a distance of about 15 km from the start of the line. The strength of the reflector A-B suggests a carbonate bed which appears to be conformable with the sediments both above and below. At the extreme south end of the profile the bed is cut by a flat lying unconformity at the base of the carbonate platform. Another readily identifiable reflector (C-D) also dips gently northwards parallel to A-B and about 500 ms deeper. Below this, the seismic images become indistinguishable, indicating the proximity of the acoustic basement. Evidence of thrust geometry is absent from the images in this segment and this suggests that the thrust faults which are illustrated in Letouzey et al (1983 Fig. 6, Profile 4) do not extend into this region. The seismic section in this region is otherwise so similar that reproduction (rather poorly) in Letouzey et al (1983 Fig. 11, reproduced here as Fig. 5.5' ; tfist some doubt is cast on the presence of thrust in this section also. Their interpret?.tion siîould therefore be questioned.

96 5.2.2 Seismic images Segment 2

The seismic images in Segment 2 (Fig. 5.6) show a prominent bathymetric depression which is characterised by strong dif&action patterns with apexes as deep as 4 s TWT, indicating that faulting may extend deep into the basement. The bathymetric depression reaches to more than 2 s TWT, implying water depth in excess of 1500 m and this, together with the diffraction patterns recognised in the images, may be interpreted as an expression of a negative flower structure, which would be a characteristic of a zone of transtensional tectonics in a strike-slip regime (Reading 1980, Park 1989). The North Sula-Sorong Fault Zone is the strike-slip system which matches this setting {cf. Fig. 1.2 and Fig. 4.1).

In the south, the seismic images show a north dipping sedimentary sequence of significant thickness (about 2 s TWT). The topmost 100 to about 300 ms TWT demonstrate a reflection pattern generated by the carbonate sequences which has been identified in Segment 1. The separation between these two horizons increases steadily from Segment 1 to Segment 2. The north dipping strong reflector at depth of about 2.8 to 3.8 s TWT is assumed to lie close to the unconformity between the sedimentary sequence and the underlying acoustic basement.

For about the first 200 ms TWT below the seafloor, the seismic images at the northern end of this segment are typified by reflection patterns which are of similar character to the patterns encountered in the southern end, i.e. reflection patterns which are generated by carbonate sequences. Strong diffraction patterns below these reflectors indicate faulting in the underlying rocks. These in turn propagate upwards forming fracture zones in the overlying sedimentary rocks which a recognizable on the images.

The characteristics of the reflection seismic images in the central part of Segment 2 suggest that the topmost rocks may have a similar character to the rocks in the southern and northern ends of the segment, i.e. carbonates. However, diffraction patterns at the seafloor are unlikely to be generated by carbonate build-ups alone. This probably is the evidence of intense and recent faulting.

97 5.2.3 Seismic images Segment 3

The seismic images in Segment 3 (Fig. 5.7) reveal a distinct asymmetrical bathymetric ridge extending for approximately 60 km. The bathymetric high on the southernmost one-third of the segment may be interpreted as representing basement rocks exposed on the seafloor and possibly forms the eastern continuation of the East Arm Sulawesi {cf. Fig. 1.2 and Fig. 4 .1). To the north of the exposed basement, the seismic images show north dipping features, which may be thrust packets, about 800 ms thick (at the thickest) directly underlain by basement. The poor quality of the images suggest that these thrust packets may have undergone intense fracturing and deformation or that they are composed of basement rocks. The thrust may be an eastern extension of the Batui Thrust {of Fig. 4.1). Further north, relatively flat-lying undeformed sediments rest on the northern slopes of the thrust packets and may be basin fill derived from lateral transport of erosion products of the East Arm of Sulawesi. The northern part of Segment 3 slopes moderately steeply into Segment 4.

5.2.4 Seismic images Segment 4

The seismic images in Segment 4 (Fig. 5.8) show a flat lying sedimentary sequence up to 1 s TWT thick in the southeastern part of the Gorontalo Basin. The seafloor is flat and at about 5 s TWT (water depth of approximately 3750 m). Acoustic basement is at about 6 s TWT. Reflection patterns provide evidence of onlap of the sediments, which may be fine clastic deposits derived from the volcanic arc in the North Arm of Sulawesi, onto a rugged basement topography.

5.2.5 Density analyses based on velocity of seismic waves

Stacking velocities listed on the seismic sections have been converted into densities using the Nafe-Drake curves (Nafe & Drake, 1957). The results are listed in Appendix F. In Segment 1, density varies from 1.92 Mg.m'^ near the sea floor at about 200 ms TWT to 2.06 Mg.m'^ at about 1000m below the sea floor (approx. 350 ms TWT), and reaches 2.34 Mg.m'^ at about 4000 m below the sea floor. The density of 2.66 Mg.m'^ reached at a depth of about 17,000 m is very close to the 2.67 Mg.m'^ average density of continental crust used as a reference density in the model studies

98 discussed in Chapter 6. This supports the contention that the Banggai-Sula continental fragment forms the basement in Segment 1 and that it has a very limited extension to the north. Only the first of the velocity analysis panels implies a density close to 2.67 Mg.m'^, while the rest of the panels along Line QS-1 indicate densities which average less than 2.40 Mg.m'^. Almost all the values in the extreme north average 2.20 Mg.m'^ or less, compatible with the average density contrast of -0.59 Mg."*'^ used by McCaffrey and Silver (1980) for Molucca Sea melange (see Fig. 4.8).

5.3 Seismicity

This section discusses the seismicity of the study area (Fig. 5.9). It focuses on the identification of events at shallow depths (less than 40 km) which are likely to be associated with strike slip movements of strands of the Sorong Fault but inevitably touches on some other features producing events within the same depth range and at deeper levels.

The seismicity data which are used in this discussion consist of geographical longitudes and latitudes and depths of earthquake foci. The source of the data was given at the beginning of this chapter. The data are presented in the form of slices oriented N-S {i.e. at right angles to the Sorong Fault Zone). Each slice covers an area one degree of longitude wide and extends from latitude 5°S to latitude 1°N. The 14 sections together cover an area from longitude 121 °E (in Central Sulawesi) to longitude 135°E (Kepala Burung) (Fig. 5.10). In order to identify tectonic features which are likely to be associated with events shown on the depth sections, reference is made to the terrane tectonic map illustrated in Fig. 4.1 and general tectonic map of the study area and the surrounding region shown in Fig. 1.2.

Depth sections 1 and 2 occupy the western termination of the Sorong Fault Zone where the Banggai-Sula microcontinent collided with Sulawesi, an episode which resulted in the formation of thrust and fold belts in the central region of Eastern Sulawesi (Hamilton 1979, Silver et al. 1983). On depth section 1, shallow events which occurred sparsely on the depth range of 40 to 100 km, situated between 2°S and 3°S may be attributed to tectonic features such as the Matano Fault Zone on the Southeast Arm of Sulawesi. This fault zone is considered to be the onshore continuation of the South Sula Sorong Fault (Fig. 4.1). Events which occurred at about the same depth

99 which are clustered a little to the north of 2°S may be associated with the response of the region to the compressive tectonics which resulted from the collision between Banggai-Sula Microcontinent and East Sulawesi. The Batui Thrust may be one of the surface manifestation of this seismicity. A dense cluster of earthquakes with focal depth of less than 100 km situated close to 0° (indicated as UNA on Fig. 5.10), appears to mark seismicity which is associated with the magmatism of an active volcano on the island of Una-Una, located in the (Fig. 1.2). A cluster of earthquake foci forming a south-dipping zone at an angle of about 56° from the horizontal and reaching depths of more than 300 km at about 0° latitude (CSL), is associated with the dipping lithospheric plate of the of the Celebes Sea. The North Sulawesi Trench (Fig. 1.2) is the seafloor feature which represents the subduction front. The subduction beneath the North Arm of Sulawesi has been regarded as producing the magmatism of the Una-Una volcano but this is situated approximately 250 km south of the trench (Bemmelen 1970, Hamilton 1979). This unusually large arc-trench gap presents problems which are outside of the scope of this thesis. On the depth section 2, the subduction related events as well as magmatism of the Una-Una volcano appear to remain as the predominant features which can clearly be identified at about 0° latitude. Sparsely distributed earthquake focal points which occurred at depth of less than 100 km and situated at the latitudes of about 3°S and 1°S may be attributed, in respective order, to the Matano Fault Zone and the Batui Thrust.

Depth section 3 remains to show the deep seated events associated with the subducting slab of the Celebes Sea lithosphere (CSL) but appears to have been interfered with the west-dipping Benioff Zone of the southern end of the Molucca Sea lithospheric plate (MSL), indicating that these two features interact in this zone. Shallower events which occurred at about 1°S with depth range of less than 100 km may be associated with the NW-SE oriented Greyhound Strait Fault (Silver et al 1983). Shallow events which are expected to have occurred at latitudes of about 3°S and 1°S have been absent, indicating that no movements of the strands of the Sorong Fault has been detected at this latitudes.

On depth section 4, indications on the movements of the strands of the Sorong Fault could not be identified. Very sparse events with randomly distributed focal points lead to uncertainty in identifying the strike slip movements associated with the strands of the Sorong Fault. Deep earthquake foci which clustered around the latitude of 0° are likely to associate with the subducting lithospheric slab of either Celebes Sea or the Molucca Sea.

100 Depth section 5 shows some seismic events which clustered around 2°S and situated at shallow depth. These may be attributed to the sliver kinematics of the Banggai-Sula Continental Fragment (BSF). A densely populated cluster of events situated in the northern part of the section from about 0° to about 1°N are likely to associate with the seismicity of the Talaud-Mayu Ridge (TMR). Deeper events which are which are randomly distributed may be associated with the descend of the Molucca Sea lithospheric plate.

Depth section 6 shows a large number of seismic events occurred at shallow depths characterised by clusters which are densely populated and almost evenly distributed throughout the region, in the sense that most events occurred at the uppermost 40 km of the section. Seismic events which occurred at about 3°S may be attributed to the thrust tectonics of the western part of the Seram Thrust Belt (STB). Earthquake foci which clustered around 2°S may be associated with sliver kinematics of the Banggai-Sula Continental Fragment (BSF) and the related strands of the Sorong Fault which, in this case, are the South Sula-Sorong Fault (SSF) and the North Sula- Sorong Fault (NSF). Seismic focal depth points which clustered between 0° and 1°N may be associated with thrust tectonics of the Talaud-Mayu Ridge (TMR).

Depth section 7 shows a considerable seismic events which occurred at shallow depth but also exhibits prominent traces of south- and north-dipping geometry. Shallow events which clustered around 2°S may be attributed to the movements of strands of the Sorong Fault which in this case, would be the eastern part of the South Sula-Sorong Fault and the western part of the North Misool-Sorong Fault. Densely populated events at shallow depth which clustered at about 1°S may be associated with movements of the Molucca-Sorong Fault. Shallow seismic events which clustered around 3°S may be attributed to thrust tectonics of the western part of the Seram Thrust Belt. The distinct geometric patterns which are delineated by shallow to deep events at about 3°S to 5°S may be associated with the south-dipping subducted slab of the Seram Trough (STS). Deeper events which occurred between the latitudes of 1°S and 1°N may be attributed to the east-dipping subducted slab of the Molucca Sea lithosphere (MSL) which caused volcanism on Halmahera as well as on islands to the west.

Depth section 8 shows a large number of shallow seismic events and prominent earthquakes related to deep seated features. Shallow events on this section may be attributed to the movements of strands of the Sorong Fault and the Seram Thrust Belt. Shallow events which clustered around 2°S may be associated with the movements of

101 the North Misool-Sorong Fault (NMS), a strand of the Sorong Fault in this region. Shallow seismic events which clustered around 3°S may be attributed to the Seram Thrust Belt. The geometric pattern which is delineated by deep seismic events between 3°S and 5°S reaching depth of about 300 km, may be attributed to the south-dipping slab of the Seram Trough (STS).

Depth section 9 shows shallow seismic events clustered between about 0° and 1°S and this may be attributed to the movements of the Molucca-Sorong Fault and probably also resulted from the compression tectonics at the terrane boundary between the West Halmahera-Tamrau (WHT) and the East Halmahera-Waigeo (EHW) provinces. It also shows a cluster of deep focal points which delineate a south-dipping geometric configuration which may be associated with the subducted slab of the Seram Trough.

On depth section 10, shallow seismic events mostly occurred on the southern part of the section from about 2.5°S to the south end of the section. These events may be attributed to the Seram Thrust Belt (STB). Seismic events which clustered around 0° may be associated with the compression tectonics on the boundary between the West Halmahera-Tamrau (WHT) and the East Halmahera-Waigeo (EHW) terranes. Seismic events which are associated with the movements of the Sorong Fault appear to have occurred only rarely.

Depth section 11 shows a clearer indication of the movements of the Sorong Fault which occurred between the latitudes of 1®S and 0° {cf. Fig. 4.1). Shallow seismic events which occurred south of 3°S may be attributed to the Seram Thrust Belt. Region between 3°S and 1°S appears to be seismically stable.

Depth section 12 shows a considerable number of shallow seismic events which occurred between 1°S and 0°. These events may be associated with strike slip movements of the Koor Fault (KF) and Sorong Fault (SF). Shallow seismic events which occurred south of 3°S are likely to associate with Seram Thrust Belt (STB).

Depth section 13 shows a considerable number of shallow earthquake focal points which may be attributed to the strike slip movements and thrust mechanism. Shallow seismic events which occurred between 1.5°S and 0° may be associated with the strike-slip movements of the Ransiki Fault (RF), Sorong Fault (SF) and Koor Fault

102 (KF). A large number of events which occurred at about 33 km were probably originated at the base of the continental crust which underlies the region.

Depth section 14 shows a large number of shallow seismic events which may be attributed to the strike-slip movements of the Ransiki Fault (RF) and Yapen Fault (YF) but most seismic events were probably originated at the base of the crust at about 33 km depth.

103 \ %

MOLUCCA SEA Oblla

Taliabu M angole

basin

SERAM NORTH BANDA SEA

Boano

Keian Manipa Kayell SORONG FAULT ZONE PROJECT Bay 4 sidescan sonar Imagery and bath Bum Seram Sea and surrounding region

% bathymetric depth In metres , contour Intervals = 500m

GLORIA track, showing width of swathe mbelau r n L\ 0 F igu re 5.1 GLORIA sidescan sonar imagery of the Seram Sea and parts of the Sorong Fault Zone ObllBtu MOLUCCA SEA

A reçlon o f moderately reflective sea floor ' without strong llneatlorts Taliabu wen defined, Mangole strong E-W lineam ent ^ - '— \ V____

parallel to bathymetric , 'X c ? 300(^^/ contour confour/Znes lines , ~ ------X ^ f - - " ^ strong SW-NE / Hr\eament ^

sea floor terraces d eep basin bathymetric showing flow direction

basin SERAM Ky r ^ g / \ / mud-volcvolcano?

Boano

submarine Ooci^eà) IÀ l/ NORTH BANDA /= = ^ , Kelàn \ Kayell ^ ^ , ^7/ \Bay_: SORONG FAULT ZONE PROJECT Line drawing Interpretation GLORIA sidescan sonar Imagery Seram Sea and surrounding region

KEY: -f.^strong multiple strong sea floor features, X / 7 ^/ {^baclfscatenlng possibly structural lineation sea floor areas with strong scattering coefficient p o ssib ly exp o sed b asem ent rocks or / ^ ? / ' " "',\N clastic sediments In channels from land areas / / / seam ount? ç r r r x oreas of particularly weak scattering, possibly 2^2^ sea floor covered by soft sediments sea floor features, showing flow direction A m b e l a u GLORIA track, showing width of swathe '12TE ^ M O " Figure 5.2 Line drawing intemretation of sidescan sonar imaaprv shown in F i o S 1 50 100

Kilometres Southeast Gorontalo Basin

Poh Head

SOUTH rs MOLUCCA SEA

PELENG

N orthw est Taliabu BANGGAI Shelf

MANGOLE LABOBO TALIABU

SALUE ISLANDS SULABESI

NORTH BANDA SEA

Figure 5.3 Approximate location of seismic lines QS-1.

106 South North SP 3000 2900 2800 2700 2600 ahelf carbonate platform

s

Figure 5.4 Segment 1 of the QS-1 seismic line, showing the characteristics of a shelf carbonate platform. The drowned platform is interpreted as the response to the sinking of the Molucca Sea lithosphere. SSE NNW East Sula Molucca Sea

sea level

Tectonic Melanges

O 00 lOKm

Figure 5.5 Seismic images reproduced from Letouzey et al. (1983), showing similar appearance to that shown in Fig. 5.4 i.e. evidence of a drowning carbonate platform. Previous interpretation indicated this as a thrust (e.g. Letouzey et al. 1983, Silver et al. 1983).

GULF O F TOMINI MOLUCCA SEA

QULf

TOLO SEftAM SEA South North SP 2600 2500 2400 2300 2200 2100 2000 1900 bathymetric depression negative flower structure

4 "

5 - s

Figure 5.6 Segment 2 of the QS-1 seismic line, showing an extensive bathymetric depression which is interpreted as indicating a negative flower structure. Strong diffraction patterns seen on the images suggest that faulting may extend deep into basement. South North SP 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 1------1------1------1------1------1------1------1------1------1------1------I------1______I______I______I______I______L_ I___ I____ I___ I___ I___ bathymetric high (exposed basement rocks)

thrust packets (?)

Figure 5.7 Segment 3 of the QS-1 seismic line, showing asymmetric ridge of bathymetric high which may be interpreted as indicating exposed basement rocks on the sea floor. Thrust packets appear to lap over the northern flank of the ridge. South North SP 800 700 600 500 400 300 200 100 0 0 — I------L I I I I 1 I___ _J __

Gorontalo Basin flat-lying sediments

acoustic basement

5 km

Figure 5.8 Segment 4 of the QS-1 seismic line, showing a flat lying sedimentary sequence of the southeastern Gorontalo Basin. Reflection patterns suggest that sediments onlap onto rugged basement topography. SORONG FAULT ZONE PROJECT Seism icity in the Sorong Fauit Zone an d the surrounding region ÔU 0‘ i|

o ' -

.* o * * *0 o ^ o s . . ..*

n " . » . . ° • ;* □ B ]0 • E3. □ , . s

2“S ■ ' • B •/.: 0 % • * * "0 ‘ > r , • O D . E P

4”S - 200 Km

NJ 120“E 122°E 124°E 126°E 128°E 130°E 132°E 134°E Longitude

Focal Depttt (Km) M wAioe m§mhw9rt rr*Mf A 0-40 41 -120 121-300 > 3 0 0 M < 5 • d o o

5

M = Magnitude of shock (Richter scale)

Knomttnt 700 V Anfcon **wmmw#.,w m * E f 5 0 f i3rE

Figure 5.9 Seismicity of tlie Sorong Fault Zone, showing the focal depths and magnitudes of shallow (0-40Km), intermediate (41-120Km), deep (121-300Km) and ver\' deep (> 300Km) events. (Data source: Tlie National Geophysical and Solar Terrestrial Data Center, NOAA, Boulder Colorado. Earthquake information based on the world-wide seismic network database 1986). Index map shows simplified tectonic of the Sorong Fault Zone. JQL - - — ■------*• — - : U.. ■ ■ 200 • -V• ■200 C S L -^-h -' 200 “ '• • 200 . m s l ". 1 MSL 1 1

Df-pth Secllon-1 Depth Seclion-2 i Depth Section-3 Depth Section-4 t ~ Depth Sections 121'E-122'E 122'E-123‘E 1 Q 123'E-124'E 1 124'E-125'E g 125'E-126'E Latitude ( * ) 2’S 0* Latitude ( ' ) 2'S O' Latitude ( ' ) 2'S O' Latitude ( ' ) 2'S O' latitude ( ' ) 2'S O'

S STB BSF TMR STB n MS MSF STB NMS N STB N STB SF A - - .j 1------•------_ *■ — — ^ — — — — — — -

200 200 . 2 0 0 ; s r s . 2 0 0 - ^ 7 200

'''■■STS 1 1 2 I U) . Depth Section-6 t Depth Section-7 Depth Section-S Depth Secthn-9 t Depth Section-10 126‘E-127‘E 127'E-128'E 128'E-129’E 129'E-130'E g 1 1 g 130'E-131'E Latitude ( ' ) 2 'S O' Latitude { ' ) 2 'S O' Latitude ( ' ) 2'S O' Latitude ( ' ) 2 'S O' Latitude ( ' ) 2 'S O'

_ ------.

200 200 200 200

E E E

Depth Section-11 i Depth Section-12 t Depth Section-13 Depth Section-14 131'E-132'E 132'E-133'E Q g 133'E-134'E 8t 1 3 4 ‘ E -1 3 5 ' Latitude ( ' ) 2'S O' Latitude (') 2'S O' Latitude ( ' ) 2'S O' Latitude ( ' ) 2 'S O'

Figure 5.10 Lithospheric sections beneath the Sorong Fault Zone and the surrounding region, showing slices of one degree depth sections oriented N-S from the longitude of 121 °E (Central Sulawesi) to 135°E (eastern Kepala Burung). Chapter 6 GRAVITY FIELD AND STRUCTURE OF THE SORONG FAULT ZONE, EASTERN INDONESIA

6.1 Introduction

The Sorong Fault Zone covers a region in which the gravity field varies over a wide range of magnitude and shows a multitude of patterns of anomaly. The variation of magnitude of free-air anomalies extends from values below -250 mGal recorded in the southern part of the Molucca Sea to values in excess of +320 mGal measured near to sea level in coastal areas of southwest Mangole and northwest Sulabesi, the two eastem islands of the Sula Group {cf. Fig. 6.1). Intermediate levels of anomalies are distributed throughout the region in a style that to some respect reflects the distribution of terranes within and surrounding the fault zone {of Fig. 4.1).

The generally E-W to NE-SW lineation of gravity contour lines is attributed to the presence of the Sorong Fault and its strands which occupy the central region of the zone extending from Kepala Burung (Irian Jaya), in the east, to the East Arm of Sulawesi in the west. The NW-SE lineation of gravity contour lines between Kepala Burung in the northeast and in the southwest is attributed to the presence of the Seram Trough {of Figs. 1.2,4.1 and 4.3). Other patterns of anomalies which are either circular or elliptical in shape may be associated with deep sea basins commonly filled with low density sediments or collision complexes which, in general, show negative anomalies {e.g. Tolo, South Molucca Sea and Seram Sea gravity lows). Circular and elliptical patterns of gravity anomalies may also be associated with isolated blocks of oceanic and arc terranes where positive anomalies are likely to be encountered due to the high density nature of these rocks {e.g. Waigeo gravity high. Obi, Ambon and Poh Head highs), except where sediment covers are thick. Examples of older volcanic or oceanic terranes, where subsidence and rate of sedimentation were high and gravity values would therefore be expected to be low, cannot be presently found in the study area except for the special case of the Molucca Sea. The elongated E- W oriented pattern of the gravity ridge which includes the islands of the Sula group and the Banggai archipelago demands a special explanation since high gravity anomalies in

114 these part of the region are associated with low density continental material which has been interpreted as being derived from the northern margin of the Australian continent {e.g. Hamilton 1979, Pigram et al. 1984). A similar although less severe, problem exists in respect of the high Bouguer gravity anomalies on Bum (Oemar and Reminton 1993) and parts of Seram. On Seram, the situation is complicated by the presence of ultrabasic rocks near Pirn Bay in the southwestern part of the island and also in the extreme south of Ambon Island (Milsom 1977).

In the Kepala Burung region and offshore to the west, the magnitudes and patterns of the gravity field (broad, circular, low gradient anomalies with Bouguer anomaly levels between zero and +50 mGal) suggest the presence of thick continental cmst beneath the region. Steeper gradients of the gravity field to the north are attributed to a transition in the nature of the cmstal materials which underlie the region. Continental rocks of Australian margin affinity are juxtaposed to arc and oceanic rocks of the Philippine Sea Plate. Zones of strike-slip faulting clearly form the boundary between these two major terranes {e.g. Pigram and Davies 1987, Dow and Sukamto 1984).

On the East Arm of Sulawesi, the onshore gravity field is poorly defined since the contour lines have been drawn by interpolating coast-to-coast measurements partly made during the course of the Sorong Fault Zone Project (onshore Gulf of Tolo and Peleng) but mostly recalculated from surveys by Silver et al. (1983). Reliance on coastal measurements alone works reasonably well on small islands but the East Arm of Sulawesi averages 50 km across, much too far for confident interpolation. Assessment of crustal structure beneath the arm requires a better definition on the onshore gravity field but expeditions of the Sorong Fault Zone Project excluded inland measurements, which were therefore not available for the present study.

6.2 Provinces of Gravity Anomalies in Sorong Fault Zone

The study area has been divided into gravitational provinces on the basis of patterns and magnitudes of the gravity field (Fig. 6.2). These are the gravity province of Kepala Burung (1), the gravity province of the North Banda Arc (2), the gravity province of the North Banda Basin (3), the gravity province of the Southeast Arm of

115 Sulawesi (4), the gravity province of the East Arm of Sulawesi (5), the gravity province of the South Molucca Sea (6), the gravity province of Halmahera (7), the gravity province of Obi (8), the gravity province of the Sula Group (9) and the gravity province of the Banggai Islands (10).

6.2.1 Gravity province of Kepala Burung (1)

The gravity province of Kepala Burung is defined here to cover the Kepala Burung area, the shelf margin areas to the north and west as well as islands to the north and west including Waigeo and the smaller islands of Batanta, Salawati and Misool.

Except in the north, the gravity province of Kepala Burung is characterised by intermediate levels of Bouguer anomalies, averaging close to +50 mGal, with sparse contour lines, showing no strong preferred lineation. This province is underlain by thick continental crust (probably everywhere thicker than 25 km and possibly in places thicker than 40 km). The continental region extends north to the Sorong and Koor faults and west to underlie Salawati and as far west of Misool at about 129°E. The notably steep gradient in the north is attributed to the change of the underlying crust from continental in the south to rocks of arc and oceanic affinities in the north. On the surface, this transition is marked by the E-W oriented Koor Fault, situated about 30 km north of Sorong Fault (e.g. Dow and Sukamto 1984, Pigram and Davies 1987). The level of Bouguer anomalies reaches more than +150 mGal in the central part of the north coast but decreases again with steeper gradients seawards (north). This abrupt change in free-air anomaly in general may be attributed to the presence of the deep water Manokwari Trough (Milsom et al. 1992a) and New Guinea Trench (Milsom et al. 1992b) situated offshore north-northeast of the Kepala Burung region. A small negative free-air anomaly with shorter wavelength occurring in shallower water at about 134°E; 0°30’S may be the expression of a small basin which probably resulted from strike-slip tectonics. The strong Bouguer gravity gradient recorded across the strait between Salawati and Batanta is attributed to the density contrast between the basement rocks which underlie Salawati in the south and Batanta to the north. Salawati is largely composed of sedimentary rocks overlying continental crust, Batanta is built up of arc volcanics. The boundary is believed to be the Sorong Fault which runs ENE-WSW through the narrow strait which separates Salawati from Batanta.

116 Further north, Waigeo and the surrounding smaller islands are characterised by Bouguer gravity field with an average level of about +100 mGal. Higher levels, of about +150 mGal, were recorded on Kawe Island to the northwest of Waigeo and in the eastern part of Waigeo itself. The generally moderately high level of anomalies in this region is attributed to the presence of rocks of oceanic origin which form the Waigeo terrane but the average level of anomaly indicates that the region is underlain by thick crust. The general pattern is consistent with an island arc origin for Waigeo.

In the east, a NNW-SSE trending gravity depression marks the Lengguru Fold Belt (Visser and Hermes 1962) which constitutes most of the neck portion of the Kepala Burung (Bird Head) region. The Lengguru Fold Belt is an area of relatively low but very rugged relief with elevations rarely exceeding 100 m above sea level (Dow and Sukamto 1984). The belt consists of clastic shelf sediments of Mesozoic age and the conformably overlying Tertiary New Guinea Limestone. These sediments are intensely folded and faulted along the northwesterly trends which follow the orientation of the neck, i.e. NNW-SSE. The sequence is underlain by Palaeozoic metamorphic basement rocks of Australian continent affinity. The level of Bouguer gravity which reaches below -80 mGal (Dow et al. 1986) suggests that the thickness of the sedimentary sequence is of the order of 7 km, at the thickest part. This estimate was made by assuming that the region is underlain by continental crust of about 30 km thick and the average density of the sedimentary rocks is approximately 2.40 Mg.m'^.

6.2.2 Gravity province of the North Banda Arc (2)

The gravity province of the North Banda Arc is defined in this study as the region which includes the Seram Sea northeast and north of the islands of Bum and Seram, the onshore areas of Bum, Seram and the adjacent smaller islands and the Banda Sea south of Bum and Seram.

In the northeastern part of the province, a NW-SE oriented fi-ee-air low where free-air gravity in general below -75 mGal is clearly associated with the Seram Trough. Water depth in this area averages about 1000 m but deepens to more than 2000 m towards the North Bum Basin in the west. Interpreted seismic sections obtain from commercial surveys (Letouzey et al. 1983) suggest that the Seram Thmst Belt is

117 composed of thrust sheets about 3 km thick {cf. Fig. 4.4). Thrust material which consists of rocks with an average density of 2.20 Mg.m'^ and the average water depth of 1500 m can account for the level of free-air gravity recorded in the area provided that the underlying crustal rocks are composed of continental material and with less than the standard thickness of 30 km. This assumes that the thrusts include large volumes of mélange and that the Kepala Burung crustal rocks extend sufficiently far to the southwest to underlie the Seram Trough and possibly also most of Seram. The level of the observed field is matched if such crust is considerably attenuated to about 20 km thick. Milsom et al. (1983) suggested as one possibility that the Seram Trough is not the result of a classic subduction of lithospheric slab and that the subduction does not and has never taken place in this area and the trough simply marks a zone of strike-slip faulting which defines the southern margin of the Sula Spur. Basement rocks of Bum and Seram have close affinity to the Kepala Burung region. The continuity of the volcanic chain of the Banda Arc may be more apparent than real; volcanism in Ambon may have been the result of isolated hot-spot activities associated with cmstal extension in Pim Bay (Milsom a/. 1983).

At the eastern end of the island of Seram, the SE-NW orientation of the anomaly trend of the Seram Trough is more or less preserved with a gentle increase in the level of the anomalies from the Seram Sea towards the southwest, i.e. inland. Elsewhere, contour trends are broadly E-W except in western Ambon and the region to the north, where contour trends tend to swing almost N-S and define stronger field gradients. North of Ambon, at the northern end ofPim Bay, a localised gravity high reaches more than +100 mGal. The strong Bouguer anomaly gradients in southern Seram and Ambon are attributed to the presence of ophiolitic rocks which outcrop in the extreme south of Ambon Island. The high level of anomalies in the northern part of the Pim Bay is also attributed to the presence of ultramafic rocks known to outcrop on the Kaibobo Peninsula (Milsom 1977).

The gravity pattern on Bum has been defined by combining offshore measurements (Bowin et al. 1980) and a single N-S profile (Oemar and Reminton 1993). A suggested position for this profile is shown in Fig. 6.1. Although its exact location was not given by Oemar and Reminton (1993), it could not, because of its length, be plausibly placed anywhere on Bum that would cause it to produce a markedly different patterns of gravity anomaly. Field gradients on the south coast of Bum are less

118 strong than those recorded on Seram and it therefore appears that the strong gradients which are commonly associated with the outer islands of the Banda Arc (e.g. Timor, Yamdena and Seram) do not extend as far as Bum. Although Bum is composed of continental rocks (e.g. Hamilton 1979, Tjokrosapoetro and Budhitrisna 1982), the overall level of the Bouguer gravity is high (up to more than +120 mGal on the southern part of the profile) and decreasing fairly gently towards the north. The lowest Bouguer anomaly recorded is about +70 mGal situated at about the centre of the profile (Oemar and Reminton 1993).

One explanation for the high gravity field on Bum is that. Bum may have been in a transpressional tectonic setting. Although it is composed of relatively low density continental materai, the transpressional tectonics may have forced higher density ductile materials which criminated in the upper mantle to flow upward, i.e. closer to the surface (e.g. McBride 1994). This may have resulted in rapid uplift, producing the steep bathymetric slopes around Bum Island.

With the present level of gravity filed and bathymetric depth, combined with the information on the average thickness and density of the sedimentary rocks (4 km and 2.30 Mg.m'^) obtained by Oemar and Reminton (1993), it is estimated that the Moho boundary is at about 21 km below sea level, implying a cmstal thickness of approximately 17 km. Bum may therefore be interpreted as underlain by considerably attenuated cmstal rocks. High heat flow to the north and south of Bum (Gool et al. 1987) may be one indication of this setting.

6.2.3 Gravity province of the North Banda Basin (3)

The North Banda Basin is a small ocean basin underlain by oceanic crust (e.g. Hamilton 1979, Bowin et al. 1980) but in places believed to be floored by fragments of continental cmstal rocks which originated as far east as the Kepala Burung region (e.g. Réhault et al. 1991,1994). The average bathymetric depth is about 4000 m and the general level of free-air gravity (about +25 mGal) suggests that sediments are thin, implying a Moho boundary at approximately 11 km below sea level in the central part of the basin.

119 The gravity province of the North Banda Basin is in general characterised by free-air anomalies averaging about zero, rising to consistently above +25 mGal in the south central part of the basin with lower levels in the northwest. Free-air anomalies of more than +50 mGal occur in places throughout the southeastern part of the basin. A localised high of more than +100 mGal occurs in the northeast at about 125°20’E; 2°40’S and a second on the western boundary of the province, north of the Wowoni Island, at 123°15’E; 3°50’S. Prominent low gravity features which may be identified in this region include an elongated gravity low which oriented ENE-WSW and situated immediately east of the Southeast Arm of Sulawesi, a N-S oriented gravity low immediately northeast of Manui Island and a NW-SE elongated gravity low southwest of Buru. The N-S elongated gravity low east and northeast of Manui appears to be an expression of the Tolo Thrust. The NW-SE oriented pattern of elongated negative gravity anomaly situated south and southwest of Buru may be interpreted as marking the West Buru Fracture Zone {cf. Fig. 1.2 and Fig. 4.1). The elongated gravity low, which oriented ENE-WSW and reached below -50 mGal, may be interpreted as indicating a zone of transtensional tectonics associated with the South Sula-Sorong Fault. The low free-air anomaly values may result from the deposition of low density sediments along the southern flank of the Banggai-Sula continental fragment. The zone extends east from south of Taliabu and continues into the Southeast Arm of Sulawesi. The southern boundary of the low may also mark the transition between the continental fragment of the Banggai-Sula Platform and the oceanic crust of the North Banda Sea {of Fig. 4.1). Water depth in this area averages about 3000 m. The sedimentary isopach map (Hamilton 1979) indicates an average thickness of about 2000 m. Assuming that the average density of the sediments is 2.30 Mg.m'^ and that the underlying crustal rock is oceanic of standard thickness, this setting would produce a free-air gravity anomaly of the order of about +100 mGal. The observed gravity field therefore requires either thicker crust of oceanic type in order to deepen to Moho sufficiently, or a fragment of continental material which is considerably attenuated. If oceanic material underlies the area, it would have a thickness of about 19 km, implying a Moho at about 24 km in order to produce the observed gravity field. If, on the other hand, the crustal material which underlies the area is composed of continental rocks with an average density of 2.67 Mg.m'^, continental crustal material would have to have been very attenuated (only about 14 km thick). This would set the level of the Moho at about 19 km and produce the level of the observed free-air gravity, i.e. -50 mGal. The gravity low extends onshore on the

120 Southeast Arm of Sulawesi where ophiolitic rocks apparently overlie schist of possibly continental origin.

Free-air gravity values exceed +50 mGal in places between Buru and the Southeast Arm of Sulawesi. Water depth in this region is on average in excess of 5000 m. Assuming that the sediment layer is thin and underlain by oceanic crust of standard thickness, i.e. 6 km, the resulting free-air gravity would be very close to zero. In order to achieve the level of the observed gravity field (about +50 mGal), the oceanic crust should be thinned to the order of less than 4 km. Bulging or arching of the oceanic crust in this region may have been the mechanism which led to the presently observed free- air gravity. Bathymetric data {e.g. Mammerickx et al. 1976, Réhault et al. 1991) show a region of high seafloor surrounded by water depth of more than 5000 m {cf. Fig. 4.3). The NW-SE oriented bathymetric high forms the Tampomas Ridge {e.g. Réhault et al. 1991). Alternatively the source of the higher gravity values may lie in the lithosphere.

6.2.4 Gravity province of Southeast Arm Sulawesi (4)

The gravity province of the Southeast Arm of Sulawesi is defined here to include part of the Gulf of Bone in the west and southwest, the Southeast Arm of Sulawesi and small islands east and southeast of the mainland including Wowoni, Manui and the Selabangka group.

In the north of the Gulf of Bone where contour lines are sufficiently well controlled, the Bouguer gravity field shows a general N-S lineation almost parallel to the orientation of the Southeast Arm itself. Onshore in the Southeast Arm, due to the lack of on-land stations, contour lines are drawn on the basis coast-to-coast interpolation. Some control is probably by a traverse across the arm immediately to the south of the map area (Silver et al. 1978). Data from the traverse were supplied by Professor E.A. Silver and were recomputed at UCL on to the IGSN 1971 standard. The resulting gravity contours appear to show a general N-S trend similar to the orientation of the Southeast Arm. Two localities which show gravity highs in the north and east of the gulf may mark the root zones of ultramafic rocks exposed onshore. Ophiolitic rocks are known to widely distributed in the Southeast Arm of Sulawesi (Silver et al. 1983).

121 They are presumably of very limited thickness because Bouguer gravity levels in the region are in general close to and, in many areas in the north, less than zero.

6.2.5 Gravity province of East Arm Sulawesi (5)

Contour lines which define the gravity field on the East Arm of Sulawesi show a NE-SW orientation which is in agreement with the orientation of the landmass itself. Although inland stations are lacking, coastal gravity data and the offshore field pattern give almost no alternative to the present contouring. The levels of Bouguer gravity are in general close to zero and the actual range may be within -25 and +25 mGal, except on Poh Head in the extreme northeast of the area where an E-W oriented elliptical pattern with higher levels of Bouguer anomaly forms a prominent feature.

About a half of the area of the East Arm Sulawesi has been mapped as exposure of ophiolite (e.g. Sukamto 1975) but the general level of Bouguer gravity does not appear to be compatible with the surface geology. However, the equally widely distributed low-density Celebes Molasse, Tertiary limestones and Mesozoic sedimentary rocks appear to be more consistent with the level of the observed Bouguer gravity field in the province. This therefore suggests that the ultrabasic rocks, where exposed, do not extend to any great depth. A block of 50 km wide and 1 km thick of ultrabasic rocks with an average density of 3.10 Mg.m'^ would generate about +17 mGal Bouguer gravity. The observed Bouguer gravity level indicates that the ultrabasic rocks may be everywhere less than 1 km thick (except on Poh Head). Given that, they generally outcrop in the mountainous region at elevations up to 2500 m. It is possible that they do not extend down below sea level. Terrain corrections would increase the Bouguer anomaly levels but measurements in this study were carried out entirely at or close to sea level, minimising the Bouguer and terrain corrections.

In the extreme northeast of the province, in the Poh Head area, Bouguer gravity reaches about +80 mGal and shows an elliptical pattern with an E-W orientation. This relatively high level of anomalies may be attributed to the sheeted dykes and gabbroic rocks which are extensively exposed in this area, particularly in the northern half of Poh Head (Silver et al. 1983). This high level of Bouguer gravity suggests that the exposed ultramafic rocks may extend about 5 km into the root zone. In the southern half of the

122 area the levels of Bouguer gravity are close to zero, consistent with the common occurrence of rocks of lower densities e.g. alluvial deposits, Celebes Molasse and Tertiary limestones.

6.2.6 Gravity province of the South Molucca Sea (6)

The South Molucca Sea region is characterised by extremely low free-air gravity (below -250 mGal in places) and a unique trilobate pattern centred at about 126°E; 0°30’S. Water depth in the region averages about 2000 m, which accounts for almost -140 mGal of the gravity effect. The remaining part of the low in the free-air gravity in this region is attributed to the presence of a collision complex (tectonic mélange) which in some areas reaches a thickness of about 15 km (McCaffrey and Silver 1980). Neither the water layer nor the collision complex appear to be locally isostatically compensated. The depression of the oceanic crust of the Molucca Sea is presumably produced by the weight of the subducted sections beneath Halmahera and Sangihe arcs.

Estimates of the crustal section in this region may be made on the basis of the gravity field. With a standard oceanic crust 6 km thick overlain by 15 km of collision complex, the Moho interface would have been situated at about 23 km below sea level and the collision complex would have an average density of about 2.20 Mg.m'^. In comparison, a standard crustal section in an oceanic environment would consists of 5 km water overlying 6 km of oceanic crust (assuming very thin seafloor sediments), i.e. a Moho interface at about 11 km below sea level. The lithospheric plate of the Molucca Sea has been subducted in the east and west under the Halmahera and Sangihe arcs and is slowly sinking, forming an inverted U-shaped geometry (Cardwell et al. 1980).

To the south and east of the South Molucca Sea province, the gravity field is characterised by steep gradients, whereas a more diffuse pattern of contour lines is observed in the west. On the southern perimeter of the province the gravity field is characterised by steep to very steep gradients, up to about 8 mGal/km, suggesting abrupt changes in the composition of the basement or crustal rocks underlying the region. However, the steepness of this gradient is more due to the transition from a low-

123 density water layer in the Molucca Sea in the north to the rocks of the Banggai-Sula region in the south. The thick collision complex may also contribute to the steepness of the free-air gravity gradient in this region. The Southern Molucca Sea region is underlain by oceanic crust which is overlain by thick tectonic mélange under water layer which can reach 2000 m depth. Results of reflection seismic surveys (e.g. Letouzey et al. 1983, Silver et al. 1983) have been interpreted as showing thrust structures composed mainly of tectonic mélange which dip north and lap over the inferred granitic rocks which constitute the basement of the Banggai-Sula Platform. The seismic sections only depict the upper several kilometres of crustal section and do not extend to the base of the crust.

A commercial seismic section used in this study does not, however, indicate the existence of any thrust structure in areas close to the boundary between the Southern Molucca Sea and the Banggai-Sula Platform. At the estimated latitude where Silver et al. (1983) and Letouzey et al. (1983) identified thrust structures, such structures could not be confirmed on the seismic section examined in this study. Instead, a drowning carbonate platform appears to be the prominent feature in about the first 25 km of the section, followed by the development of a negative flower structure about 20 km wide which is probably resulted from the transtensional kinematics of the North Sula-Sorong Fault (cf. Section 5.2).

At the eastern rim of the province, the steepness of the gradient of the gravity field is partly also attributed to the change in the underlying crustal rocks where the Molucca Sea crust in the west is juxtaposed against the Halmahera arc terrane of the Philippine Sea Plate in the east (e.g. McCaffrey and Silver 1980, Hall et al. 1987) but the water-to-rock transition appears to be the predominant factor. The more diffuse pattern of the contour lines at the western periphery of the province may suggest that, although abrupt changes may occur in the composition of the crustal rocks, these changes occur beneath the thick layer of low-density tectonic mélange and, being at great depth, produce gentler gravity gradients. In this part of the region, the oceanic crust of the Molucca Sea in the east is juxtaposed against the volcanic terrane of the North Arm Sulawesi in the west (e.g. Katili 1978, Hamilton 1979). The nature of the contact between these two differing terranes is not presently known and is beyond the scope of the present study which deals with the structure of the Sorong Fault Zone.

124 The western part of the South Molucca Sea province includes the Gorontalo Basin. A deep basin which is underlain by ophiolitic basement similar to rocks found on the East Arm of Sulawesi (Silver et al. 1983). Katili (1978) interpreted the small deep-sea basins surrounding Sulawesi, e.g. the Gorontalo Basin in the north and Bone Basin in the south, as originally formed in the interdeep part of the arc-trench gap of the Miocene Sulawesi double island arcs. This interdeep, which initially had a N-S orientation, is now represented by the landmass of Central Sulawesi which is referred to as the median zone. The Bone Basin in the south has more or less maintained its original N-S orientation whereas the Gorontalo Basin in the north now has an E-W orientation and contains an active volcano, Una-Una. This could perhaps be the only example in the world of an arc-trench gap which is occupied by an active volcano.

The Gorontalo Basin is situated to the northeast of the Poh Head area where water depth averages about 4000 m. The northern part of the seismic section analysed in this study {cf. Section 5.2) shows a flat lying sedimentary layer about 2000 m thick. The recorded free-air gravity in the central part of the basin is on average about -75 mGal. This implies that, if the underlying crustal rock of the Gorontalo Basin is of oceanic type, they must be at least 12 km thick i.e. twice the thickness of standard oceanic crust. If, however, the underlying crustal rock of the Gorontalo Basin is of arc- volcanic origin, a thickness of approximately 10 km would be required to produce the level of the observed free-air gravity in the region. It may therefore be interpreted that underplating of the oceanic crust and volcanic rocks may have occurred at the boundary between the South Molucca Sea crust and the arc-volcanic terrane of the North Arm Sulawesi.

The Bone Basin is situated in the southwest comer of the study area. Analysis of the structure of the basin has been carried out by Guntoro (1995) using seismic profiles and gravity data obtained from commercial surveys. Results from one of the analyses (Line IND07) indicate that the northern part of Bone Basin is in general underlain by low-density material on oceanic crust of non-standard thickness. The oceanic crust appears to be slightly thinner than standard but the Moho is at about 20 km (Guntoro 1995). Another interpreted section (Line INDl 16) situated in the extreme south of the basin indicates that the region is underlain by thickened oceanic crust (about 12 km) and the Moho is situated at about 15 km below sea level (Guntoro 1995).

125 6.2.7 Gravity province of Halmahera (7)

The gravity field of the Halmahera province is characterised by moderate to high levels of Bouguer anomaly ranging from +25 mGal in the east to more than +200 mGal in the west. The NW-SE oriented contour lines with anomalies o f+100 mGal or higher are typical of an active volcanic island arc {e.g. Vening Meinesz 1954, Heiskanen and Vening Meinesz 1958). The continuity of the NW-SE oriented belt of gravity high is disrupted by the presence of a region where the Bouguer gravity falls to a level of less than +75 mGal. This region of low gravity is associated with the continental rocks on Bacan. The extent of the low suggests that the continental rocks of Bacan continue in the subsurface to the west coast of Halmahera.

Offshore in the eastern part of Halmahera province, in the Weda Bay region, the free-air anomaly averages about +25 mGal. Water depth in this region is on average about 1000 m, which on its own can account for about +50 mGal of the reduction of the generally high level of gravity anomaly observed on Halmahera. Assuming that the region is underlain by basement rocks of oceanic affinity with a standard thickness of 6 km, about 10 km thick sediments with an average density of 2.30 Mg.m’^ would be required to produce the observed free-air gravity. The sediment isopach map in the Weda Bay region (Hamilton 1979) and seismic profiles obtained from commercial surveys indicate that sediments are in fact nowhere more than a half of the thickness estimated above, suggesting that they overlie a thicker crustal layer, i.e. eliminating the possibility that the Weda Bay is underlain by oceanic crust of a standard thickness. 4 km of sediments overlying crust of about 22 km thick, i.e. Moho at about 27 km, would produce the level of observed free-air gravity in the region.

If the basement were composed of continental rocks with an average density of 2.67 Mg.m"^, the base of the crust would have been at about 21 km below sea level. This would imply that the crust is severely attenuated, being only 16 km in thickness. In such a setting, heat-flow should be markedly elevated. Fragments of crustal materials with continental character may have been transported from the northern margin of the Australian continent (the Kepala Burung region) by strike-slip kinematics along strands of the Sorong Fault and accreted to form the basement in the Weda Bay region. This setting implies a trapped crustal fragment with a sedimentary basin resting on top. Immediately to the southeast of the Weda Basin, the Salawati Basin contains sediments

126 of about the same order of thickness as those in the Weda Basin but the Salawati Basin overlies continental crustal and has a level of free-air gravity similar to that in the Weda Basin. The Salawati Basin is underlain by thicker crustal rocks (Untung and Barlow 1981). Results of the investigation conducted by Enterprise Oil Company and PERTAMINA (1990) indicate that the Weda Basin is underlain by continental crustal rocks which probably form a continuation from the Bacan block in the west to the southern part of the basin. Sodik et al (1993) interpreted the pre-Miocene sediments of the Weda Basin as composed mainly of clastic quartz, reflecting the acid crystalline provenance of the basement rocks.

If, on the other hand, the basement of the region is composed of arc-volcanic rocks with an average density of 2.72 Mg.m'^, the base of the crust would have been situated at about 23 km below sea level. This suggests that the volcanic basement was sufficiently thick to depress the Moho sufficiently to produce the observed level of the free-air gravity. Heat flow might still be sufficiently high because the region is close to an active volcanic island arc. On the basis of field geology {e.g. Sukamto et al 1986, Hall et al 1987), the western half of Halmahera is underlain by basement which is composed of arc-volcanic and volcaniclastic rocks whereas in the east the basement is composed of ophiolitic rocks of the Philippine Sea Plate. Interpreted seismic Line PAC313, obtained from commercial surveys (Hall et al 1987), indicated that the basement of the southern part of the Weda Basin is composed of arc-volcanic and volcaniclastic rocks whereas in the north the basement is interpreted as a transition zone between these two types of rocks. The Weda Basin is therefore probably underlain by rocks transitional between arc-volcanic and ophiolitic.

High level of Bouguer anomalies of more than +200 mGal which is recorded in the extreme northwest of the Halmahera province may be attributed to the presence of the Tawali Formation (Hall et al 1987, Malaiholo 1993) which commonly consists either of pillow basalt of arc-related character with associated hemipelagic rocks (the Jojok Member) or volcaniclastic turbidites associated with debris flows and red mudstones (the Marikapal Member). The high level of Bouguer gravity in this area appears to be more compatible with the Jojok Member.

127 6.2.8 Gravity province of Obi (8)

The gravity province of Obi is characterised generally by moderate to high levels of anomaly ranging from around +50 mGal (free-air anomaly) in the offshore areas surrounding the main island of Obi to a Bouguer gravity maximum of more than +150 mGal in the central inland area of Obi itself. Maximum water depth reaches about 2000 m south of Obi, more than 2000 m to the west in the area adjacent to the South Molucca Sea region and only about 1000 m north and east of the island.

Important geological features which may be identified in this region include the Obi Basin offshore east of Obi and the ophiolitic rocks of Obi which commonly outcrop in the northeastern half of the island. The Obi Basin contains about 1000 m of sediments {e.g. Hamilton 1979) under about 1000 m water depth and is characterised by free-air gravity averaging about +50 mGal. This suggests that the basin is definitely not underlain by oceanic crust of standard thickness (assuming that the density of the sediments is similar to those in the Weda Basin immediately northeast, 2.30 Mg.m'^). Oceanic crust which underlies this basin would need to thicken to more than 25 km to produce the observed gravity effect which seems extremely unlikely. A more probable solution to this is that the Obi Basin is underlain by considerably attenuated continental crust with a thickness of approximately 20 km. Another possibility is that the basin is underlain by crustal rocks of arc-volcanic type with a thickness of about 23 km in order to achieve the same effect in the observed free-air gravity.

The high level of Bouguer gravity on Obi may be attributed to the presence of ophiolitic rocks which outcrop in the west and northeastern parts of the island and suggests that the ophiolites may extend deep into a root zone. A more detailed analysis on the geometry of the ophiolites on Obi is discussed in Section 6.3.4.

6.2.9 Gravity province of the Sula Group (9)

The gravity province of the Sula group covers the islands of Taliabu and offshore west to about 124°E, and the islands of Mangole and Sulabesi, offshore north to about 1°15’S, south to about 2°30’S and offshore east to about 127°E. The region contains one of the most remarkable features of the global gravity field. Bouguer

128 gravity levels of more than +300 mGal are exceedingly rare in land areas and where they do occur, as in the western Pacific Bonin forearc (Tanaka and Hosono 1974, Karig and Moore 1975), they are usually associated with oceanic rocks which has been raised to high levels in the crust. However, the Sula Islands gravity high, which reaches to a maximum value of about +320 mGal at the northern end of Sulabesi and southwestern part of Mangole (Fig. 6.1), is associated with a sliver of continental crust, evidently derived from the northern margin of the Australian continent, in which metamorphic basement of Palaeozoic age (van Bemmelen 1970, Hamilton 1979) is intruded by Permo-Triassic granite and overlain by contemporaneous acid volcanics. The basement complex is unconformably overlain by continental to shallow marine coarse-grained elastics of Early Jurassic age (Garrard et al. 1988), which in turn are conformably overlain by black, restricted marine shales and claystones of Late Jurassic to Early Cretaceous age.

The positive anomaly has roughly the same shape in plan as the Sula Islands themselves but extends west to include, although at significantly reduced levels, the islands of the Banggai group. A complicating factor in plan views of both gravity and topography/bathymetry is the southward protrusion associated with Sulabesi Island, which has an anomalous N-S orientation. Any explanation for the gravity feature in region must clearly take into account the continental nature of the Sula Islands themselves, the proximity of the Molucca Sea with its extraordinary low fi-ee-air gravity field (McCaffrey and Silver 1980) and the presence of the oceanic crust of the North Banda Basin in the south (Bowin et al 1980). It also has to be noted that the gravity high continues as a strong linear feature to the east of Sulabesi and therefore to the east of the limits of the North Banda Sea oceanic crust {cf. Fig. 6.1).

One of the most striking aspects of the Sula anomaly is the extreme linearity of the contour lines which define its northern limits. Linearity is also a characteristic of the contours on the southern side, except where they are distorted across the northern part of Sulabesi. If all gravity data in this sector, from about 126°45’E; 2°S to 126°15E; 2°30’S were to be excluded from the database, continuous E-W Bouguer gravity contour lines could be easily drawn from Taliabu to eastern Mangole, almost precisely parallel to the south coasts of these two islands. In view of this fact, it appears reasonable to assume that the very high Bouguer anomalies in northern Sulabesi are produced by merging the effects of two separate anomalous mass distribution, one

129 associated with the Mangole-Taliabu block, the other with Sulabesi. The form of the gravity feature produced by Sulabesi alone has been estimated by removing from the map the effect of the Mangole-Taliabu masses to construct a residual anomaly map of Sulabesi. This was a vital initial stage in the interpretation process. Contour lines were then drawn from Taliabu to Mangole based on assumptions of minimum and maximum curvature. The residual anomalies based on these assumptions are shown in Fig. 6.3 and Fig. 6.4, along with an estimated 'most plausible' version upon which quantitative interpretation has been based. It can be seen that the two extreme versions of the residual gravity map are in fact very similar. Their most outstanding characteristic is the relatively small extent to which they share the strong N-S elongation of Sulabesi itself. The gravity anomaly, although not fully equidimensional, is elliptical rather than circular and is centred in the area slightly to the south of the centre of the island.

The crustal models shown in Figs. 6.3 and 6.4 were initially analysed using two- dimensional (2-D) modelling, but in view of the limited N-S strike extent of Sulabesi, the two-and-a-half dimensional (2!6-D) responses of the models (Section 3.2) were also evaluated. The total N-S extent of Sulabesi was taken as approximately five times its cross-strike width, the line of gravity profile being at about one cross-strike width from the southern end. When modelling was repeated using these strike limits, differences from the 2-D computed values did arise but were not very significant, given the size of the anomaly. The computed gravity using the 2!6-D approach was, on average, about 6 mGal less than the gravity computed using 2-D techniques. As can be een m Figs 6.3 and 6.4, where dots are used to show the 2-D computed gravities and continuous lines to show the 216-D equivalents, this difference is almost invisible on profiler drxvr. a. reasonable scale. The differences may imply that the continental sliver which fc .irs Sulabesi is about 0.4 km thicker than would be deduced from the 2-D modelling.

The pattern of the gravity contours would have been simpler, with only a prominent E-W elongated gravity high covering the Sula Islands, were it not for the complication of the N-S contour trends caused by Sulabesi. One possibility is that the island of Sulabesi was originally the southeastern part of what is now Mangole Island. The growth and dispersion of the Sorong Fault into its present configuration may have

130 led to the separation of Sulabesi from Mangole. Clockwise rotation of Sulabesi may have been the principal movement, accompanied by a small amount of translation leading to the present configuration and producing the unique pattern and magnitude of the presently observed gravity field in the region. It is speculated that the break-up between Mangole and Sulabesi may have been initiated by the splitting of the Sorong Fault Zone into the North and South Sula-Sorong faults {cf. Fig. 6.5). The island of Sulabesi apparently formed the transfer zone which accommodates the movements of the South Sula-Sorong Fault. Detailed analysis of crustal structures beneath the Sula Islands region is presented in sections 6.3.1 and 6.3.2.

6.2.10 Gravity province of the Banggai Islands (10)

The gravity province of the Banggai Islands is defined here to include the islands of the Banggai group which consists of Peleng, Banggai, Bangkurung, Labobo, the Salue group and the surrounding offshore area {of Fig. 6.2). Gross geological features of the Banggai group are similar to the Sula group where Palaeozoic metamorphic basement is intruded by Permo-Triassic granites and overlain by acid volcanic rocks of similar age {e.g. Hamilton 1979, Garrard et al. 1988).

The free-air gravity field in the Banggai Islands region is in general characterised by circular contours with magnitudes between zero in the north, west and south to about +125 mGal towards the east on the Banggai continental fragment. The circularity of the contour lines is the most noticeable feature of the western part of the province and may be attributed to the geometry of the collision margin between the Banggai-Sula Microcontinent and the East Sulawesi terrane. The generally high level of gravity field may be attributed to the attenuated continental crustal rocks which constitute the Banggai province, i.e. an elevated Moho topography which chiefly accounts for the level of the recorded gravity field. A detailed analysis of crustal structure in this region is discussed in Section 6.3.3.

At the collision margin in the west, crustal rocks may be thickened considerably, forcing the Moho sufficiently deep to produce the low level of gravity field. A gentle gradient in the west appears to suggest a gently easterly dipping collision interface which accommodates the mechanism of obduction of scrapped oceanic materials onto

131 the East Arm of Sulawesi {e.g. Silver et al. 1983). On the northern side of the province, field gradients are in general also low. Reflection seismic images located close to the northeastern part of the province {cf. Section 5.2) indicate a drowning carbonate platform and show a generally gentle bathymetry with an average depth of less than 1000 m. Steep gradients of the gravity field at the south side of the province may be attributed to the transition between the basement rocks of the Banggai Islands to the deep water and sediments in the northwestern part of the North Banda Basin. Water depths in this region average to about 3000 m and sediment layers reach 3000 m thick (Hamilton 1979).

6.3 Structure of the Sorong Fault Zone

This section discusses the analyses of crustal structure of the Sorong Fault Zone in terms of gravity models. Four selected profiles were manually digitised from the gravity map shown in Fig. 6.1 and analysed using the GM-SYS™ modelling software. As is often the case with gravity model analysis, the model which do not, and cannot produce the observed gravity field are as important as, and in many cases more important than those which produce acceptable level of agreement with observation. The models used have been controlled, where this is possible, by actual geology and reflection seismic data but, in the interest of exploring all possibilities, considerations of geological probability have been introduced only at a fairly late stage.

One of the major influences on the gravity field, and hence one of the main constraints on the modelling, is the shape of the seafloor. In order to define this effect for modelling purposes, it is necessary to first define a standard crustal model which produces zero Bouguer anomaly at the surface of the Earth (Fig. 6.6). In the present study, this background model is defined as a standard continental crust with a density, in its upper part, of 2.67 Mg.m'^, a thickness of 30 km and density contrast across its base (the Moho discontinuity) of 0.4 Mg.m'^. The pattern of the density variation between the Earth’s surface and the Moho is undefined but it is assumed that most of the necessary increase takes place at mid-crustal levels. This allows the 0.4 Mg.m"^ contrast across the Moho interface to be used even where the crust is considerably less than 30 km thick and also allows a sea water layer to be modelled with a density contrast of -1.64 Mg.m'^, regardless the water depth. Continental crust with these characteristics is in isostatic

132 equilibrium with oceanic crust 6 km thick, with a mean density of 0.1 Mg.m ' gie&ter than continental crust and overlain by 5 km of water. This gross but convenient oversimplification places some limits on the reliability of the deduction which can be drawn firom the analysis but these are not usually of critical geological importance.

The other important parameter in the gravity modelling is the density values which are assigned to each crustal layer. Gravity modelling in this study made use of six types of crustal layer i.e. standard continental crust, oceanic crust, transitional crust, sea water, sediments and collision complex (tectonic mélange). Although the analysis of crustal model used density contrasts as one of the parameters for computing the gravitational effects of each crustal layer, rock types and their average density values may be assigned as follows. Standard continental crust is represented by granitic rocks with an average density of 2.67 Mg.m'^. Oceanic crust is represented by basaltic layer with an average density of 2.77 Mg.m'^. The transitional crust may be represented by arc-volcanics with an average density of 2.72 Mg.m'^. The average density for sea water is 1.03 Mg.m*^. Sediments are represented by crustal layer with an average density within the range of 2.3 Mg.m’^to 2.4 Mg.m'^. Collision complex is represented by crustal layer with an average density of 2.2 Mg.m’^.

Density analysis based on the velocity of seismic wave along the QS-1 profile located offshore northwest of Taliabu (discussed in Chapter 5), showed that density varies fi-om about 1.75 Mg.m"^ to 2.2 Mg.m'^ near seabottom and reaches to about 2.34 Mg.m'^ at depth of about 1000 m m below seafloor. The highest density obtained in this analysis was 2.66 Mg.m'^ and found at depth of about 4000 m. This value is very close to the average density of the standard continental crust i.e. 2.67 Mg.m"^, used as the reference density in the gravity modelling discussed in Chapter 6. The density values which fall within the range of 1.75 to 2.2 Mg.m'^ appear to be compatible with various rock types, ranging firom soft and uncompacted sediments to tectonic mélange of the South Molucca Sea. The density values of about 2.35 Mg.m'^ may represent carbonate rocks. Results of this analysis are tabulated in Appendix F, Table F.l.

Analysis of seven rock samples collected firom Sula Islands also showed that the density of continental rocks fall within the range of 2.52 Mg.m'^ to 2.65 Mg.m'^ (close to 2.67 Mg.m’^ used as the background density for standard continental crust). The basic rocks, which probably are altered, fall within the density range of 2.38 Mg.m'^ to

133 2.79 Mg.m’^ (close to the density value assigned for oceanic crust used in the modelling i.e. 2.77 Mg.m"^). Analysis for ultrabasic rocks results in density values within the range of 2.62 Mg.m’^ to 3.08 Mg.m'^ (close to the density of the upper mantle material used in the modelling i.e. 3.07 Mg.m'^). Results of this analysis is tabulated in Appendix F, Table F.2.

Additional information which were obtained from a commercial source (Milsom pers. comm. 1997), indicated that density values of crustal rocks in the Kai Region (situated southeast of the study area), fall within the range of 1.6 Mg.m'^ to 1.9 Mg.m’^ for Quaternary sediments (probably uncompacted), 2.2 Mg.m'^ to 2.3 Mg.m'^ for accretionary prisms and thrust sheets, and 2.68 Mg.m'^ for the Palaeozoic basement (close to the density value assigned for the standard continental crust used in the modelling i.e. 2.67 Mg.m'^). Information from this source is tabulated in Appendix F, Table F.3.

Four gravity profiles are here presented for analysis to deduce the structure of the crust under which profiles were taken. These are located in western iviangole, fiie shelf region west of Taliabu, the Banggai Islands and the Obi region (Fig. 6.7).

6.3.1 Crustal structure of Western Mangole Island

The gravity profile analysed in this section extends for about 200 km from the North Banda Sea region in the south, across the western part of Mangole Island and then into the Southern Molucca Sea region (Fig. 6.8). Offshore in the Central North Banda Sea region, free-air gravity averages about +50 mGal but the field increases very rapidly from about +100 mGal to more than +300 mGal within 20 km of the south coast of western Mangole. This steep gradient (about 10 mGal/km) is apparently due to the steep bathymetric changes from the deep sea basin of the North Banda region to the shelf region south of Mangole Island. The composition of the underlying crustal crustal rocks appears to change as well but the extreme steepness of the field gradient appears to be less compatible with this transition. On western Mangole, Bouguer gravity reaches a maximum value of about +320 mGal on the south coast and decreases fairly rapidly to about +200 mGal along the north coast at a rate of about 8 mGal/km. Offshore north of Mangole the free-air gravity values further decrease at about the same rate from around

134 +200 mGal to a value of less than -100 mGal at the northern end of the profile in the Southern Molucca Sea region. The steep gradient to the north is also due to the high density contrast between the continental crust beneath Mangole and the water layer of the Molucca Sea. Thick tectonic mélange beneath the Southern Molucca Sea may also contribute to the steepness of the gradient of the fi*ee-air gravity field but apparently less significant than the effect caused by the crust-to-water transition.

The modelled crustal section consists of, in the south, a thin layer of sediments under seawater which averages 4 km deep but deepens to about 5.5 km in the region close to the estimated location of the South Sula-Sorong Fault. The oceanic crust of the North Banda Sea, of standard thickness (6 km), overlies the Moho at approximately 11 km below sea level. The crustal block beneath Mangole is modelled as composed of continental rocks with an average density of 2.67 Mg.m"^, lying directly on the Moho. The Southern Molucca Sea region is modelled as containing at least 5 km, but in extreme cases up to 10 km, of thick tectonic mélange (mean density 2.20 Mg.m'^) in about 2 km of water. The mélange is underlain by standard oceanic crust directly in contact with the Moho.

Figure 6.9 illustrates the process by which the final model for this area was obtained, beginning by computing the effect of the water layer alone and following this with computations which include the effect of interfaces which cannot be directly observed. Each calculated profile is shown accompanied by the observed profile along the same line, so the two can be directly compared.

Figure 6.9a illustrates the water layer effect. In the North Banda Sea, the 4 km depth of water can account for a negative fi:ee-air anomaly of about -275 mGal. Near the South Sula-Sorong Fault Zone it produces nearly -380 mGal firee-air gravity. In the Southern Molucca Sea, the 3 km deep water contributes almost -210 mGal to the firee- air gravity (Fig. 6.9a). With the general level of the presently observed fi-ee-air gravity in this region (solid circles in Fig. 6.9a), it is necessary to raise the Moho considerably to compensate for these extremely low values. Fig. 6.9b shows crustal section, consisting the North Banda Sea, the Mangole continental block and the Southern Molucca Sea with the Moho situated at about 11 km below sea level {i.e. at the level of the standard oceanic Moho).

135 Raising the Moho produces good agreement between the computed and the observed free-air gravity field in the North Banda Sea to the south of the shelf margin of Mangole and even better fit is achieved for the southern flank of the Mangole gravity high. However, large discrepancies amounting as much as 240 mGal, on the northern side of the profile, in the Southern Molucca Sea region. This large mismatch between the calculated and the observed free-air gravity fields can be minimised by drastically lowering the Moho level beneath the Molucca Sea to about 26 km below sea level, which requires a Moho dip north of Mangole of about 20° (Fig. 6.9c). This implies that the crust under the Southern Molucca Sea region is composed of rocks of continental origin. Results from previous geophysical studies in the Southern Molucca Sea region (e.g. Silver et al. 1983, McCaffrey et al. 1981, McCaffrey and Silver 1980), indicate however, that the crust consists of thick layer of tectonic mélange underlain by oceanic basement of unknown thickness and attitude. In this study, to a first approximation, the oceanic basement of the Southern Molucca Sea is assumed to have a standard geometry, i.e. to 6 km thick and horizontal, and to underlie a thick layer of low-density tectonic mélange. Seismic sections (Silver et al. 1983) located close to the northern part of the analysed gravity profile interpreted as showing that the upper part of the mélange is thrusted but presumably these thrust, if they exist at all, are only superficial.

The modification to the model shown in Fig. 6.9c involves resetting the Moho closer to surface (about 16 km below sea level), while at the same time introducing about 5 km of low-density tectonic mélange under about 3 km of sea water (Fig. 6.9d). The resulting free-air gravity appears to be in close agreement with the observed field. Introduction of standard oceanic crust (6 km thick) at depth of about 12 km would, because of its positive density contrast of 0.1 Mg.m'^, slightly increase the computed free-air, hence widening the disagreement between the model and the observed field. This may, however, be balanced by thickening the tectonic mélange and to some degree by modifying the geometry of the Mangole continental fragment. Any modification to the thickness and extent of the continental fragment under northern Mangole must, however, take into account the tectonic setting in this region. One possible modification of the model is that shown in Fig. 6.9e. This model shows almost 7 km thick tectonic mélange in about 3 km water, overlying standard oceanic crust vyith Moho at about 15 km below sea level.

136 The high Bouguer gravity on Mangole appears to demand extremely thin crust beneath the island (11 km thick at the thickest). Thinner crust in the south must be assigned to the oceanic basement of the North Banda Sea (Fig. 6.9f). In this region however, the oceanic crust of the North Banda Sea also appears to be non standard, being less than 6 km in thickness. One further geological constraint however, demands a layer of sediment, which may be thin, overlying the oceanic basement. A thin sedimentary layer would replace the higher density oceanic crust and therefore reduce the computed free-air gravity field and hence widen the disagreement between the model and the observed gravity values. In order to compensate for this, the oceanic crust of the North Banda Sea must, because the bathymetric constraints cannot be altered, be adjusted by raising the Moho to a higher level (Fig. 6.9g). Following this adjustment, the oceanic crust of the North Banda Sea is everywhere, in this section, less than 6 km and has an arching geometry. This may be interpreted as a result of the compressive shear kinematics introduced by the merging effect of the movement of the Sorong Fault Zone system and the sinking of the lithospheric plate of the Molucca Sea.

In view of the shear tectonics in this region, the Sula Islands might be expected to be the expression of a positive flower structure. Such a structure, along with its gravity effects is shown in Fig. 6.9h. The drastic reduction in the values of the computed gravity field across the Mangole high is due to the attempt to accommodate the crustal base to the typical geometry of a positive flower structure i.e. in this case, the Moho is set lower. This indicates that any model with a geological cross-section of this type will not produce the very high gravity values required in the centre of the profile. The Mangole gravity high appears to demand a high level Moho under the island. The other critical aspect in the modelling of this profile is the thickness of the tectonic mélange in the Southern Molucca Sea region. These appear to be the predominant parameters which control the geometry of the crustal structure in the central and northern side of the profile. In order to replicate the Mangole high, it is necessary to set the Moho at a high level. The Molucca Sea gravity low may be achieved by making the tectonic mélange thicker.

Setting the Moho up at about 14 km beneath the northern part and about 10 km beneath the southern of the Mangole Island appears to produce the required match in the centre of the gravity high. Increasing the thickness of the mélange to about 9 km i.e. depressing the Moho under the Molucca Sea to about 18 km appears to produce an

137 acceptable level of agreement between the model and the observed field (Fig. 6.9i). The model shown in Fig. 6.9j is an alternative crustal structure. The only difference is that, the model shown in Fig. 6.9i includes an extensive, although thin, sediment layer in the North Banda Sea and the model shown in Fig. 6.9j assumes that the sediments in general accumulated only in the area close to the zone of the strike-slip faulting (the South Sula-Sorong Fault). This gives a chance to make the oceanic crust of the North Banda Sea slightly thicker and to improve the level of agreement between the computed and the observed gravity fields.

The problems which remains with the model is that the oceanic crust of the North Banda Sea appears to be unacceptably thin in comparison with normal oceanic crust, although the model shows a good fit. This may geologically be interpreted as local thinning (?) of the oceanic crust in the region along the South Sula-Sorong Fault. Crustal bulging or arching may have occurred widely in the North Banda Sea region (e.g. Réhault et al. 1991,1994) and the anomalously thin oceanic crust in this region may be attributed to this phenomenon. Figure 6.10 illustrates one possible crustal structure beneath the western Mangole region, showing the gravitational effects of each crustal layer as well as the effect of all layers which formed the crust beneath the region.

6.3.2 Crustal structure of the shelf region West Taliabu

The structure of the crust beneath the shelf region west of Taliabu Island was explored using a N-S gravity profile which extends for about 350 km from the North Banda Sea in the south, then across the shelf and then north into the Southern Molucca Sea region (Fig. 6.11). The Molucca Sea section of this profile is more or less coincident with the seismic line QS-1 discussed in Chapter 5 and bathymetric depths in this region were therefore constrained by the sti^i ?! : iii^ . T^. e cai^mic tine also provides a certain amount of subsurface information which can oe :.issd to constrain the modelling although, unfortunately, the control on the gravity field is rather poor in the northern part of the profile.

In the North Banda Sea, the free-air gravity averages about +50 mGal at the southern end of the profile but decreases to less than -25 mGal in the area about 100 km from the beginning of the profile. The free-air gravity field then rises from a minimum

138 of about -25 mGal to more than +150 mGal in the shelf region west of Taliabu. To the north of this region the free-air gravity decreases fairly rapidly at a gradient of approximately 5 mGal/km from about +100 mGal in the area immediately northwest of Taliabu to less than -150 mGal further north in the southwest Molucca Sea region. Still farther to the north, the free-air gravity field increases very gently from about -150 mGal to -125 mGal but slightly steeper along the last 25 km towards the northern end of the profile where free-air gravity reaches -75 mGal.

As with the crustal model of Western Mangole, the structure beneath the shelf region of Western Taliabu is modelled as consisting of, in the south, a thin layer of sediments under sea water which averages 4 km depth. The sediments overlie the oceanic crust of the North Banda Sea (6 km standard thickness) which directly rests on the Moho at about 11 km. The crustal block beneath the shelf is modelled as composed of rocks of continental origin lying directly on the Moho. The Southern Molucca Sea region is modelled as containing at least 8 km of tectonic mélange. In extreme cases the mélange which is modelled as having average density of 2.20 Mg.m'^ and under, on average, 3 km of water could be as thick as 15 km. Beneath the mélange is oceanic crust of standard thickness which rests directly on the Moho.

The sequence by which the crustal model in this region was obtained is shown in Fig. 6.12. Figure 6.12a illustrates the gravitational effects of the water layer of the North Banda and the Southern Molucca seas. The 4 km (average) water depth in the North Banda Sea region produces a free-air gravity level of the order of -300 mGal and in places even lower. In the Southern Molucca Sea region, the 2 km (average) water depth produces about -150 mGal of free-air gravity. The average level of the free-air gravity low in the region requires the Moho to be set at about 20 km below sea level in order to compensate for the gravity effects of the sea water (Fig. 6.12b). This produces an average level of free-air gravity field of about +50 mGal in the Southern Molucca Sea region and about -100 mGal in the North Banda Sea region. Large discrepancies between the computed and observed gravity field in the southern part of the profile may be reduced by raising part of the Moho beneath the North Banda Sea to about 11 km below sea level, i.e. by introducing a crustal section with standard oceanic thickness (Fig. 6.12c). This produces fairly good agreement between the computed and the observed free-air gravity field in the southern flank of the high with a minor discrepancies to the south. These appear to demand a slightly higher Moho level i.e.

139 introduce an arching geometry of the oceanic crust of the North Banda Sea ' ^lustal model Western Mangole). The oceanic crust of the North Banda Sea appears to be thinner than a standard, i.e. less than 6 km thick, in order to achieve a good match to the observed free-air gravity in this area. Addition of a thin layer of sediments improve the agreement between the computed and the observed free-air gravity field (Fig. 6.12d).

The observed free-air gravity gravity low in the Southern Molucca Sea appears to demand normal oceanic crust beneath a thick layer of tectonic mélange. Introduction of about 10 km thick low-density tectonic mélange (2.2 Mg.m"^), Fig. 6.12e, decreases the computed gravity field by about 200 mGal, giving a fair level of agreement on the northern flank of the gravity high.

Large discrepancies to the north appear to demand a thinner layer of mélange. The oceanic crust is situated at shallower depth and the Moho is therefore, higher. The agreement between the computed and observed free-air gravity in the northern part of the section is further improved by introducing a crustal block with a density contrast 0.05 Mg.m'^ at the northern end of the section, representing the arc-volcanic rocks of the North Arm Sulawesi (Fig. 6.12f).

Minor disagreement on the northern flank of the gravity high (Fig. 6.121) may be minimised by the introduction of a crustal block with a wedging geometry, having a density contrast -0.27 Mg.m'^, representing carbonate platform which developed as a result of subsidence caused by transtensional kinematics of the North Sula-Sorong Fault in the area (Fig. 6.12g).

The best match between the computed and observed free-air gravity on the northern flank of the gravity high was achieved by the introduction of another block with a lower density contrast (-0.47 Mg.m"^) which may represent reef build-up, resting on top of the platform (Fig. 6.12h).

Close to the northern end of the section, the model suggests that the mélange thins out and juxtaposes against the arc-volcanics of the North Arm Sulawesi. The average thickness of the volcanic block is about 15 km. At the boundary between the mélange and the arc-volcanics the Moho is situated at about 15 km below sea level.

140 Figure 6.12h shows the final model of the crust beneath the shelf region west Taliabu. The crustal model suggests that the oceanic crust of the North Banda Sea is covered by a layer of sediments which is everywhere about 1 km thick or less, and that the crust is less than 6 km thick and showing an arching geometry. The Moho in the North Banda Sea region is situated at about 10 km below sea level but is shallower in places. This, as with the crustal structure analysed for the western Mangole profile, may be interpreted as due to regional doming of the oceanic crust of the North Banda Sea {e.g. Réhault er ûf/. 1991,1994).

In the central part of the section, the generally high level of free-air and Bouguer gravity must be attributed to the high level of the Moho rather than to the presence of the continental fragment. The continental crust which constitutes this region may be approximated by a rectangular block about 20 km thick which dips southwards at approximately 35°.

The crustal section beneath the Southern Molucca Sea consists of about 13 km thick tectonic mélange in the central part of the transtensional zone where a block of oceanic crust is down faulted, depressing the Moho to about 22 km below sea level. In this area the gravity model correlates well with the interpretation of the seismic profile QS-1 discussed in Section 5.2 of this thesis. The southern part of the extensional faulting shown in the model is compatible with the extensive bathymetric depression recognised in the seismic profile QS-1 (Fig. 5.4 and Fig. 5.6) which can be interpreted as the seabottom expression of a negative flower structure. Such a structure may have developed as a consequence of the interaction between shear movements along the Sorong Fault system and the descent of the lithospheric plate of the Molucca Sea. Figure 6.13 illustrates the gravitational effects of each crustal layer as well as the effect of all layers which constitute the crust beneath the shelf region west Taliabu.

6.3.3 Crustal structure of the Banggai Islands

The gravity profile analysed in this section extends for about 300 km from the northwestern part of the North Banda Sea in the south, across the Banggai Islands and then north into the southwestern part of the Molucca Sea (Fig. 6.14). In the North Banda Sea region the free-air gravity varies from about -25 mGal at the southern end of

141 the profile to about +100 mGal at the shelf margin south of the Banggai Islands. In the shelf region where water depths are less than 200 m, and onshore on the Banggai Islands, free-air and Bouguer gravity increases from about +50 mGal in the south to a maximum value of about +125 mGal in the centre of the region and then decreases to approximately -50 mGal across the shelf region towards the Molucca Sea. Free-air gravity gradients of about 5 mGal/km on both south and north of the Banggai Islands high are primarily due to the transition from low density sea water to rocks which formed the Banggai Islands.

The crustal structure in this region is modelled as consisting of, in the south, a layer of sedimentary rocks in the Tomori Basin (Hamilton 1979) beneath water layer of the North Banda Sea and overlying crustal rocks which are probably of continental character. The crustal block in the centre represents the micro-continental mass of the Banggai Islands which occupies about 150 km of the overall section. In the north, the model consists of the water layer of the southwestern part of the Molucca Sea, which averages about 3 km, overlying a considerable thickness of tectonic mélange (about 3 km on average and thicker in places). The mélange is underlain by oceanic crust of standard thickness i.e. 6 km.

The sedimentary sequence of the Tomori Basin is thought to be composed of carbonate and clastic rocks of Miocene age (Charlton 1995, 1996). The sequence reaches about 3 km thick in the deepest part of the basin (Hamilton 1979). The water depths in this part of the North Banda Sea range vary between 3 and 4 km. The crustal block which underlies the basin is modelled as consisting of rocks of continental origin similar to those of the Banggai Islands.

Figure 6.15 illustrates the sequence by which the final model of the crustal structure of the Banggai Islands was obtained, starting with evaluating the effects of water layer alone and following this with the computation which include the effect of interfaces which cannot be directly observed. Figure 6.15a shows the gravitational effect of the water layer. In this part of the North Banda Sea where water depth averages about 3.5 km, the computed gravitational effects produce a minimum value of about -240 mGal. In the southwestern part of the Molucca Sea the effect of the water layer is about the same as that computed for the North Banda Sea. With this level of free-air gravity, it is necessary to raise the Moho to about 20 km below sea level to

142 compensate for the negative free-air gravity effect produced by sea water. Figure 6.15b illustrates a preliminary stage of the crustal model, showing reasonable agreement between the computed and the observed free-air gravity field at the southern flank of the gravity high but a considerable mismatch in the northern half of the profile is obvious. A thick layer of tectonic mélange (about 13 km) is introduced in the northern half of the section to reduce the level of the computed free-air gravity in this region. A 13 km thick tectonic mélange is required if the oceanic crust of the Molucca Sea is 6 km thick, which places the Moho at 20 km. The water depth over the thickest part of the mélange is about 1 km (Fig. 6.15c). With this model, the computed free-air gravity reaches as low as -250 mGal and the maximum discrepancy against the observed field is of the order of 150 mGal. The presence of oceanic rather than continental crust in the Molucca Sea (Fig. 6.15d) does not significantly improve the agreement between the computed and the observed gravity field because a 6 km thick oceanic crust with a density contrast of 0.1 Mg.m"^ only produces about 25 mGal gravity effect. It is therefore necessary to set the Moho higher and make the mélange layer thinner.

Figure 6.15e shows a crustal model with tectonic mélange about 8 km thick at its thickest and the Moho situated at about 16 km below sea level. The northern part of the profile shows good agreement between the computed and the observed field but discrepancies are obvious at the northern flank of the gravity high. This mismatch could be reduced by modifying the geometry of the interfaces between either the mélange and the northern side of the continental fragment or the Moho and the base of the continental fragment (Figs. 6.15f and 6.15g). Both models show an acceptable level of agreement between the computed and the observed gravity field but the one shown in Fig. 6.15f appears more plausible and was therefore chosen as the basis for the next step in the developing the crustal structure in this region.

The southern part of the section includes a layer of sediments in the Tomori Basin with a thickness manually digitised from the sedimentary isopach map published by Hamilton (1979). This information provides some degree of control to the crustal model constructed for this region. The introduction of sediments with a density contrast of -0.37 Mg.m'^ obviously produces a lower level of computed free-air gravity field in this region because the sediments geometrically replace the higher density crustal material (Fig. 6.15h). If the sediments were underlain by normal oceanic crust i.e. 6 km thick with a density contrast of 0.1 Mg.m"^, the Moho would have been at about 12 km.

143 because the thickest sedimentary basin is about 6 km. Setting the Moho at this level produces a computed free-air gravity of the order o f+100 mGal, implying a maximum discrepancy of approximately 80 mGal between the computed and the observed field (Fig. 6.15i). Matching to the observed free-air gravity in this region can, at this stage, only be done by setting the Moho lower and hence thickening of the crustal block beneath the sedimentary basin. With the density contrast for the crustal block maintained at 0.1 Mg.m'^, it is necessary to thicken the crust to about 14 km, implying the Moho at 20 km below sea level (Fig. 6.15j). If this is the case, underplating of oceanic crust may have occurred beneath the region and local subsidence may have been markedly rapid. Field observations during the gravity expedition of the Sorong Fault Zone Project in the coastal area west of the Tomori Basin suggested some degree of subsidence in the area. This is indicated by destruction of a village at Tanjung Lingkobu (gravity station 93017), part of which has been covered by water during high tides. For this reason, the local authority has established a new settlement further inland and ordered the people of the existing village to leave the coast.

If, on the other hand, the crust beneath the Tomori Basin is of continental type, a thickness of about 11 km is required to obtain an acceptable match between the calculated and the observed free-air gravity field (Fig. 6.15k). Further refinement on the geometry can result in the crustal model illustrated in Fig. 6.151, which shows an improved level of agreement between the computed and the observed gravity field. Other possibilities for the crustal structure of this region are shown in Fig. 6.15m and Fig. 6.15n. In Fig. 6.15m the contact between the tectonic mélange and the continental fragment is steeper than shown in Fig. 6.15n. This requires adjustment to the northern part of the base of the continental fragment e.g. by setting the Moho slightly lower in comparison with structure shown in Fig. 6.151. The crustal structure shown in Fig. 6.15n offers a simpler geometry at the base of the continental fragment (ductile deformation may result in the simplest geometry) but more complex geometry developed in the upper part of the crust (the contact between the mélange and the continental fragment) to compensate for any discrepancy caused by making the Moho geometry simpler.

In all cases however, the crustal model shown in Figs. 6.151, 6.15m and 6.15n suggest that stretching of the continental fragment may have occurred in the Tomori Basin. This may be the result of the transtensional shear along the South Sula-Sorong

144 Fault Zone. The development of the Tomori Basin may therefore be interpreted as the result of an extensional faulting of the continental crustal block. The model shows that the continental fragment which underlies the basin is about 9 km thick, i.e. severely attenuated continental fragment. With this crustal setting, heat flow would have been significantly high which might have promoted the maturation of the hydrocarbon reserve in the Tomori Basin. However, heat flow information in this area is not presently available and the interpretation was purely based on the gravity data. Heat flow measurements in this area and the surroundings may provide key information to resolve the ambiguity in interpreting whether the crustal block beneath the basin is of thickened oceanic crust or a stretched continental fragment. Cool, dense and thick oceanic crust would be expected to yield low value of heat flow but a stretched continental fragment might produce high level of heat flow.

In the central gravity high, the obsevations suggest that the base of the continental fragment beneath the Banggai Islands is situated at about 20 km below sea level. In view of this interpreted geometry, it has been assumed that the region of the Banggai Islands is an expression of a positive flower structure and is therefore situated in the transpressional part of the shear zone along the Sorong Fault system in this region. The deep basins to the south and southwest may represent the transtensional part of the shear zone.

The crustal structure in the northern part of the section suggests that the mélange may be as thick as 8 km and overlies a standard oceanic crust which is in direct contact with the Moho at about 16 km below sea level. It also indicates that the mélange laps over the continental fragment, forming a complex wedge (Figs. 6.151 and 6.15m). A crustal structure with a more complex geometry is shown in Fig. 6.15ii. Ihe gravitational effects of each crustal layer as well as the effect of oX\ layers which composed the crust beneath the Banggai Islands region is shown in Fig. 6.16. The computed 2V2-D gravity response of the crustal model appears to be lower (13 mGal, on average) compared to the 2-D approach. This may imply that the continental fragment which formed the Banggai Islands region could be thinner by about 0.8 km and the Moho situated slightly higher. The 2!6-D effects were evaluated in view of the finiteness of the crustal blocks towards the west-northwest where the terrane of the Banggai Islands collided with the East Sulawesi terrane. The west-northwest portion of

145 the crustal section was assigned to extend to about 100 km (instead of to infinity) but the east-southeast portion is left with the previous extent i.e. infinity.

6.3.4 Crustal structure of the Obi region

The gravity profile analysed in this section extends for about 200 km firom the Northern Seram Sea region in the south, across the island of Obi and then north into the strait of Obi which separates Obi from the Southwest Arm of Halmahera (Fig. 6.17). The southern end of the gravity profile runs almost parallel to the gravity contour lines with averages values, for the Seram Sea, of about -25 mGal. Towards the south coast of Obi, Bouguer gravity values range from about +80 mGal along the south and north coasts to about +150 mGal in the central part of the island. A localised low with values below +100 mGal occurs on the west coast. Offshore north of Obi the free-air gravity decreases from about +125 mGal on the north coast to about +30 mGal over the deepest part of the Obi Strait and increases again to about +100 mGal southeast of Bacan and southwest of the SW-Arm of Halmahera. Offshore east of Obi the free-air gravity decreases from about +125 mGal at the eastern end of the island to an average value of about +50 mGal in the area of the Obi sedimentary basin (Section 6.2.8). Offshore west of Obi the free-air gravity values decrease very sharply from about +100 mGal on the west coast to about -200 mGal in the southeastern comer of the Molucca Sea. A steep gradient which averages about 6 mGal/km, appears to suggests abrupt changes in the composition of the underlying crustal material but may alternatively be an indication of the presence of low-density tectonic mélange of the Molucca Sea. However, the water- to-crust transition in most cases greatly contributes to the steepness of the field gradient. The mélange may possibly extends as far east as the Obi Strait but it is also possible that the strait is underlain by undeformed sediments. Crustal models which illustrate these two possibilities are presented below. In regard with the limitation on the strike extent of the crustal block which constitutes Obi, the 2!4-D response for this cmstal section were examined.

In view of the proximity of Obi to the Kepala Burung region, it appears logical to assume that the entire cmst beneath the southern part of the profile is composed of continental rocks and that the continental cmst may also extend further beyond the

146 analysed profile. The analysis below investigates whether this hypothesis is compatible with the gravity observations.

The crustal structure finally modelled in this region consists, in the south, of a water layer with an average depth of about 3 km overlying a layer of sediments. The sediment overlie either standard oceanic or attenuated continental crust. Beneath Obi Island the model consists in the southern part of a continental fragment and in the north of a block of ophiolitic rock. The ultramafic blocks on Obi are modelled to consist of a high density peridotitic layer in the south and at depth, with an overlying basaltic layer in the north. Offshore north of the island, the modelled section consists of a water layer of about 1 km depth and a layer of sedimentary rocks which are underlain by oceanic crust apparently of non standard thickness. At the northern end of the profile the crustal section consists of a relatively high density block, representing the arc-volcanic terrane of the southwest arm of Halmahera.

Figure 6.18 illustrates the process by which the crustal model of the Obi region was developed. Analysis began with the calculation of the gravitational effect of the water layer. The 3 km deep water in the northern Seram Sea region would, by itself, contribute almost -210 mGal to the free-air gravity, while the 1 km of water in the Obi Strait produces about -70 mGal (Fig. 6.18a). Setting the Moho at about 20 km then produces a general level of free-air gravity close to that observed in the region (Fig. 6 .18b). Discrepancies on either side of the central gravity high have been minimised by setting the Moho beneath the central part of the island to about 27 km, leading to the model shown in Fig. 6.18c, which suggests that the deep crust beneath Obi may consist entirely of continental rocks. The residual Bouguer gravity high on Obi appears to be an expression of a localised block of high density rocks close to the surface; a match cannot be achieved by variation in the depth of the Moho alone, because of the long wavelength of Moho effects. The short wavelength of the residual high in the central part of the profile requires a smaller crustal feature situated at a shallower depth. Figure 6.18d shows a preliminary crustal model, with a high density near-surface block which produces the required level of computed Bouguer gravity. The model suggests that this high density block extends only to about 3 km below sea level.

147 Field geology (e.g. Hall et al. 1992) suggests that ophiolitic rocks outcrop extensively on Obi, The model shown in Fig. 6.18d uses a density contrastibr the peridotitic member of the ophiolite association of 0.4 Mg.m'^. At the other extreme, i.e. where basalt is the only rock of the ophiolite association present, a density contrast of 0.1 Mg.m'^ is used. A model which produces a close match to the observed gravity field is shown in Fig. 6.18e. This model shows that the basaltic block would have to extend to about 10 km depth to produce a reasonable match between the computed and the observed gravity field and that the discrepancy of about 30 mGal in the central high cannot be elimin#edl)y abasaltlayer alone. The gravity data seem to demand rocks of higher density in the vicinity of this high.

Studies of the ophiolitic rocks of Obi (Agustiyanto 1995) suggest that these grade from peridotite in the west to gabbro, dolerite and basalt in the east. The gravity profile used in this analysis makes a rather oblique angle with the line of gradation and therefore only a small portion of the basaltic layer beneath the Bouguer gravity high was replaced by denser material. This was however sufficient to produce the required level of agreement between the computed and the observed Bouguer gravity (Fig. 6.18f). The model shows that the western part of the dipping slab consists of a layer of peridotitic rocks with a density contrast of 0.4 Mg.m'^ with standard crust.

The introduction of the basaltic layer beneath Obi requires oceanic crust to be incorporated as the northern continuation of the dipping basaltic layer and the crustal model in the northern half of the section has therefore been modified. Figure 6.18g illustrates one possible model, with a sedimentary layer approximately 10 km thick beneath about 1 km of water and underlain by standard oceanic crust. The Moho is at about 17 km. The thick layer of sediment might consist of tectonic mélange similar to the rocks which form the upper crust of the Molucca Sea region. The obducted basaltic layer with its northern continuation into oceanic crust may also be similar to the oceanic crust of the Molucca Sea. The crustal model in Fig. 6.18g shows that it is possible that the basic rocks on Obi result from obduction of oceanic crust which brought parts of the upper mantle to high levels and emplaced them above continental crust. The obduction angle suggested by the model is about 25°.

148 Discrepancies, which would be about 80 mGal, between the computed and the observed free-air gravity at the northern end of the profile have been minimised by introducing a crustal block with a density contrast of +0.05 Mg.m'^, representing the arc-volcanic terrane of the southwest arm of Halmahera (Fig. 6.18h). With this block in place, a more elaborate adjustment has been made to the dipping basaltic layer to obtain a better match to the northern flank of the central Bouguer gravity high (Fig. 6.18i).

The southern half of the section appears to consist mainly of continental crustal rocks overlying the Moho at about 20 km. Discrepancies between the computed and observed free-air gravity in this area have been minimised by raising the Moho. However, Avithout the presence of a sedimentary layer beneath the water, adjustment of the Moho alone would not produce the required match since some of the discrepancy is represented by a short wavelength gravity variation which must originate in the upper crust (Fig. 6.18i). It was therefore necessary to introduce a near surface layer to produce the required effect. Introduction of sediments, which are less dense than standard crust, initially produced a larger discrepancy and it was necessary to raise the Moho still higher. With this and appropriate shaping of the sedimentary layer, the computed field was brought into close agreement with observation.

Interpretations of a seismic line situated about 100 km east of the gravity profile (Letouzey et al 1983) show at least 2 km of sediments in the southern part of the line. Using this information as an additional constraint produced the model in Fig. 6.18j. The remaining discrepancies have been minimised primarily by raising the Moho level and adjusting the geometry of the base of the sedimentary layer (while maintaining a more or less a constant thickness of about 2 km for the sediment). Setting the Moho at about 15 km produces a good match at the southern flank of the free-air high but fails to replicate the observed field south of the inflection point of the observed free-air values (Fig. 6.18k). Further attempts to match the observed free-air gravity using a crust of standard density lead to a unacceptably thin crustal layer (Fig. 6.181). It is therefore appropriate, at this stage, to assign oceanic crust in this part of the section and adjust its thickness to obtain the closest possible agreement between the computed and the observed free-air gravity (Fig. 6.18m). More elaborate adjustments result in the crustal

149 model shown in Fig. 6.18n, which produces computed gravitational efifects which closely match those actually observed.

The model shown in Fig. 6.18n illustrates a crustal structure consisting of, in the south, oceanic crust apparently slightly thinner than normal, underlying about 2 km of sediments, with the Moho at about 12 km below sea level. The oceanic rock is probably a remnant of Indian Ocean crust. Continental crust appears to extend south of Obi for about 50 km. In southern Obi it seems that a thin sheet of ultramafic rock is thrust over fairly thick continental crust, while in the northern part of the island a thick basaltic layer is interpretd as overlying the dipping ultramafic sheet. The basic rocks appear to have been emplaced along a high angle thrust fault which may be one aspect of shear tectonics along the strands of the Sorong Fault system, in this area the Molucca-Sorong Fault. Offshore, in the Obi Strait, the crustal section consists of about 10 km of sediments in water approximately 1 km deep. The sediments are apparently underlain by thin oceanic crust overlying the Moho at about 16 km. In the model, the sedimentary layer is assumed to have a density contrast of -0.37 Mg.m'^ with standard crust. If these sediments are similar to the tectonic mélange of the Molucca Sea (Fig. 6.18o), then the oceanic fragment also could have originated in the Molucca Sea. The principal difference between the models shown in Fig. 6.18n and 6.18o is in the thickness and density of the sedimentary layer and consequently in the level of the Moho. The model in Fig. 6.18o includes a thicker layer of lower density tectonic mélange than the model shown in Fig. 6.18n.

At the northern end of the section, the model consists of a block of relatively high density material representing the arc-volcanic terrane of the southwest arm of Halmahera. The block extends down to a Moho at about 23 km below sea level. Modelhng in this region is schematic only, since its purpose is to gain insights into the Sorong Fault Zone rather than Halmahera. Figure 6.19 shows, for one selected model, the gravitational effects of each crustal layer, as well as the combined effect of all layers. The model was prepared using the 2V^-D approximation, although the results of 2 D modelling are included for comparison. The difference between the two is equivalent to the effect of a small change in the regional background.

150 'yauLF ' OF ; TOMINI

MOLUCCA Am

SALAWATI' V

' PAJAAHPAT ISLANDS ummsi SalawatlGULF

H \ MISOOL ooXz^j, SVLABESI

SERAM

Selabangka Is. 3°Sw GULF SERAM OF NORTH BURU BONE 1/ BANDA

Manui

BANDA

132°l Figure 6.1 KEY: Gravity contour map of the Sorong Fault Zone (Bouguer on land, ffee-air offshore). The map his Coastal/inland gravity stations been drawn using data acquired during the course of the Sorong Fault Zone Project and other | Marine geoptiyslcal survey tracks available data. The gravity expeditions of the Sorong Fault Zone Project consisted of measurentents Gravity contour intervals - 25 mGal along the coast of islands within and surrounding the fault zone. Other data which were available to On Buru and Obi Indicated by contour latiels the present study included those from marine geophysical surveys (Bowin et al. 1980), on-landland coastal surveys of Irian Jaya and the surrounding area (CROC 1985) and parts of Central Sulawesi 151 (Silver et a/. 1983) I Weda HERA Basin

TANTA

SALAWATI <^Obi RAJAAIAPAT

Bintuni

JAYA BURU

AMBON

BANDA

127°E, iar.Ei 1 3 3 ! E d, free-air offshore). The map has ; Fault Zone Project and other j e Project consisted of measurements . Other data which were available to :ys (Bowin et a l. 1980), on-landland 985) and parts of Central Sulawesi oronlalo • wÂioeo.'^ Manokwar! Trough Basin ; Weda auLF Basin OF III : TOMINI hHead ' m m SororiflF»^? SOUTH HALMA HERA MOLUCCA SEA y ARM 4 YÈPALA 0 o IPELENO MMAUPAT': ' %URUNQY*\^ V'^s SULAWESI //.I Basin. .f.-Salawad GULF GGA Basin OF ISLANDS TOLO ^. 08/ K 8 SULA .SULABESiyr^ 'i Ï GROUP North 'SERAM. ■iiiS IRIAN JAYA Trough

NORTH \LCMr>Wi BANDA BASIN SOUTH, NORTH ARI BANDA ARC I SULAWESI Lr\ m \ llL l__ iM i____ / y Its-e. \ : r t o

1 Gravity province of Kepala Burung 5 Gravity province of East Arm Sulawesi Gravity province of the Sula group

2 Gravity province of the North Banda Arc 6 Gravity province of South Molucca Sea 10 Gravity province of the Banggai Islands

3 Gravity province of the North Banda Basin 7 Gravity province of Halmatiera

4 Gravity province of the Southeast Arm Sulawesi 8 Gravity province of Obi

F igu re 6 .2 Gravitational provinces of the Sorong Fault Zone SULABESI \ , ISLAND \ n 200 \ gravity anomalies I ^ ------200 I 100 Seram Sea North Banda Sea 50 iVesf \ \ E ast V Line of Residual gravity 0 profile Regional gravity trend SORONG FAULT ZONE PROJECT Residual Gravity Anomalies Map -1 Minimum curvature regional trend ,SULABESI SULABESI ISLAND

•------50 Regional gravity trend 50 ■------Residual anomalies

400 U 200

« -200

- 4 0 0

0 W est North Banda Sea Sulatiesi Island Seram Sea East -0 37 -1 64 10 20

30 -4 0 -20 0 20 40 Distance (km) VE = 0 5

-t- Observed gravity " . Computed gravity (2-D) . Computed gravity (2'A-D)

01 -0.37

Sula continental upper mantle Seram Sia crust Seram Sea sediments fragment North Bandi Sea crust North Banda Sea sediments (oceanic)

Generated with GM-SYS TM

• cT», UOLUCCA

f e BANDA

Figure 6.3 Residual gravity anomaly of Sulabesi Island based on the minimum curvature regional trend (a), along with the crustal section (b) modelled from the anomalies.

153 SULABESI ISLAND Residual W 2“S gravity anomalies

Seram Sea North Bandage

W est Line o f R esidual gravity 0 profile Regional gravity trend SORONG FA UL T ZONE PROJECT Residual Gravity Anomalies Map • 2 Maximum curvature regional trend tuSULABES! SULABESI ISLAND______

^ " ------50 Regional gravity trend ^ Residual anomalies

West Nortt) Banda Sea Sulabesi Island Seram S ea E ast -1 .6 4 - 0 .3 7 I ,0 0.1 00 0 1 QI 20

30 -40 -20 0 20 40 V E = 0.5 Distance (km)

Observed gravity . Computed gravity (2-D) . Computed gravity (2%-D)

0 4 0.1

Sula continental upper mantle Seram Sea crust Seram Sea sediments fragment North Banda Sea cwst North Banda Sea sediments ( oceanic )

Generated with GM-SYS

Gut^oFTomm • d n .

GULF « a

Figure 6.4 Residual gravity anomaly of Sulabesi Island based on the maximum curvature regional trend (a), along with the crustal section (b) modelled from the anomalies.

154 Taliabu Mangole

Taliabu Mangole

Taliabu 4 Mangole^

Taliabu 5 Mangole^

6 Taliabu

Figure 6.5 Break-up of Sulabesi from Mangole. Pattern of the gravity field in the region may have been simpler with Sulabesi attached to Mangole. Shear along the Sorong Fault system may have caused the pattern of gravity field to evolve from the simplest form i.e. only E -W oriented elongation (1) to a more complicated blend of N -S and E-W trends (6). The numbered sequence 2 through 5 indicates the proposed scenario of the break-up.

155 SORONG FAULT ZONE PROJECT Standard crust for model analysis 400 200 zero zero o Bouguer gravity free-air gravity & 0 levels ^ V levels t o -200 ------; computed gravity Generated with GM-SYS ™ -400

sea se a wafer Earth surface surface density contrast - -1.64 Mg.m -3 L/x 0 - ON 5 km Continerxtal crust Oceanic crust 6 km 10 - density contrast - 0.1 Mg.m -3 Î Average density = 2.67 Mg.rrf^ f - Density contrast = 0.0 Mg.nf^ 0 20 - Upper mantle 19 km Q Standard thickness = 30 km density contrast = 0 .4 Mg.m 30 -

-200 -100 100 200 V.E. = 2 Distance (km)

Figure 6.6 Standard crustal section used as the basis for analysing the gravity models in this study. GULF OF TOMINI Halmahera MOLUCCA SEA Bacan

East Arm

Banggai n

Ambon U\ <1

-j Line of gravity profile of Western Mangole Interpreted seismic profile East Obi LS-S1

2 Line of gravity profile of Western Taliabu Interpreted seismic profile West Obi LS-S2

3 Line of gravity profile of the Banggai Islands Interpreted seismic profile Northeastern Mangole ES-S2

4 Line of gravity profile of the Obi region Interpreted seismic profile Northwestern Mangole ES-S4

Seismic profile Northwestern Taliabu QS-1

Figure 6.7 Lines of gravity profiles analysed in this study, showing the approximate locations of seismic sections used for providing some degree of controls to the crustal models. SE NW 80 Distança (Km) 40 -200' NW

100- ES-S2 & ES-S4 I ,000. SE t Sula Thrust IQü I m tigo- - SE TAUABÙ - MANÛOLi 4000 Line: ES-S2 'SULABESI 100 NORTH SE BANDA 100 SEA Distance (Km) 40 20

Ê Sula Thrust t 2000 00 50 100 & Kilometres I I 4000 U n e: ES-S4

SEA Figure 6.8 Line of gravity profile across western Mangole Island, showing the lines of seismic sections ES-S2 and ES-S4 interpreted by Silver et a i (1983). 400 « 200 H r OH 2 -200 —

South North Banda Sea West Mangole South Molucca Sea North

0 - -1.64 -1.64 0.0 1 0 -

2 0 -

-1 5 0 -100 -5 0 0 50 100 150 V .E . = 2 Distance (Km)

4 0 0 « 200- >' I -200 —

-4 0 0

South North Banda Sea West Mangole South Molucca Sea North

0 - -1.64 -1.64 0.0 1 0 - 0.4

2 0 -

-1 5 0 -100 -5 0 0 50 100 150 V .E . = 2 Distance (Km)

KEY: # observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37 sea water Sula continental upper mantle oceanic crust Molucca Sea North Banda Sea crust tectonic melange sediments Generated with GM-SYS Figure 6.9a and 6.9b An early stage crustal model for the western Mangole region, showing (a) the gravitational effect of the water layer of the North Banda and South Molucca seas, (b) The calculated free-air gravity brought into general agreement with observation by raising the Moho to about 11 km.

159 400 200 —

-200 — CD

South North Banda Sea West Mangole South Molucca Sea North 0- -1.64 -1.64 E 10 — 0.0

8- 0.4 o 20-

-1 5 0 -100 -500 5 0 100 150 V.E. = 2 Distance (Km)

4 0 0 5 200 — É 0 — - s -200 — CD -4 0 0

North Banda Sea West Mangole South Molucca SeaSouth North 0 - -1.64 0.0 -0.47 10- 0.4 I 20 —

-1 5 0 -100 -5 0 0 50 100 150 V .E . - 2 Distance (Km)

KEY: observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Sula continental upper mantle oceanic crust Molucca Sea North Banda Sea crust tectonic melange sediments

Generated with GM-SYS

Figure 6.9c and 6.9d (c) The introduction of a dipping Moho beneath the South Molucca Sea region appears to produce the required level of the observed free-air but implies a thick layer of standard continental crust, (d) Introducing low-density tectonic mélange about 5 km thick allows reduction in the thickness of the crust to reach the thickness of standard oceanic crust.

160 400 g 200 H

O -200 — -4 0 0

North Banda Sea West Mangole South Molucca SeaSouth North

0 — -1.64 -1.64 0.0 -0.47 0.1 1 0 - 0.1 0.4

20 —

-1 5 0 -100 -5 0 0 50 100 150 V .E . - 2 Distance (Km)

200 —

g -200 — ^00

South North Banda Sea West Mangole South Molucca Sea North

0 — -1.64 -0.47 0.1 0.0 10 — 0.1 0.4

20 —

-1 5 0 -100 -50 0 50 100 150 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Sula continental upper mantle oceanic crust Moiucca Sea North Banda Sea crust tectonic melange sediments

Generated with GM-SYS ‘

Figure 6.9e and 6.9f (e) The introduction of oceanic crust on both sides of the section appears to produce an improved match between model and observation and (f) incorporation of a thin sedimentary layer in the North Banda Sea appears to reduce the level of the match (f).

161 400

I -200 — (3 -4 0 0

South Banda Sea West Mangole South Molucca SeaNorth North 0- -0.37 -1.64 -1.64 0.0 -0.47 10- 0.1 0.1 0.4 20-

-1 5 0 -100 -5 0 0 50 100 150 V.E. =2 Distance (Km)

40 0 « 200-1 •f" 0 — S -200 — (3 -4 0 0

North Banda Sea West Mangole South Molucca SeaSouth North 0- -0.37 -1.64 -1.64 0.1 ■0.47 10 - 0.0 0.1

20 — 0.4

-1 5 0 -100 -5 00 50 100 150 V.E. = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Sula continental upper mantle oceanic crust Molucca Sea North Banda Sea crust tectonic meiange sediments

Generated with GM-SYS

Figure 6.9g and 6.9h (g) A better match in the North Banda Sea region may be achieved by further raising the Moho and hence thinning the oceanic crust; (h) an attempt to introduce a typical positive flower structure into the model fails to produce the level of the observed gravity field in the region.

162 400 200- 0- 2 -200 —

-4 0 0

North Banda Sea West Mangole South Molucca SeaSouth North

0- -1.64 -0.37 -1.64 0.1 0.0 10- -0.47 0.4 0.1 20-

5 0 5015 0 -100-5 00 5 0-1 100 150 V.E. - 2 Distance (Km)

4 0 0 200- 0- 2 -200 —

-4 0 0

South North Banda Sea West Mangole South Molucca Sea North 0- -0.37\ -1.64 -1.64 0.1 0.0 10- 0.4 0.1 20-

-1 5 0 -100 -5 0 0 5 0 100 150 V .E . - 2 Distance (Km)

KEY: • obsenred gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Sula continental upper mantle oceanic crust Molucca Sea North Banda Sea crust tectonic melange sediments

Generated with GM-SYS

Figure 6.91 and 6.9j (i) Possible crustal structure of western Mangole, showing a thin but extensive layer of sediments in the North Banda Sea (j) similar model but with deposition of sediments restricted to the area close to the zone of the South Sula-Sorong Fault.

163 Gravity effect of sea water 200 - 0 - oI -200 — ■400

4 0 0 Gravity effect of tt)e upper mantle 200 - 0 - o -200 ^00

4 0 0 Gravity effect of tfte oceanic crusts 200 - 0 - a -200 - -4 0 0

4 0 0 Gravity effect of the Molucca Sea tectonic melange 200 - 0 - (D -200 - -4 0 0

4 0 0 Gravity effect of the North Banda Sea sediments 200 - 0 -

CD -200 - -4 0 0

4 0 0 Overall gravity effect of 200 - crustal structure western Mangole f CD -200 -

-4 0 0

South SouthNorth Western North Banda Sea Mangole NSSF Molucca Sea -1.64 -1.64 0.1 0.0 10 - -0.47 0.4 0.1 20 -

-100 0 100 V .E . = 2 Distance (km)

SSSF: South Sula-Sorong Fault KEY: observed gravity computed gravity NS SF: Nortth Sula-Sorong Fault

-1.64 0.0 0.4 0.1 ■0.47 -0.37

sea water Sula continental upper mantle oceanic crust Molucca Sea North Banda Sea fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.10 One possible crustal structure beneath western Mangole, showing the individual and overall gravitational effects of the crustal layers.

164 North 50 100 -100 Kilometres

MOLUCCA / SEA

South Molucca Sea — 100

BANGGAI

W e s t, LABOBO Taliabu Shelf , TALIABU MANGOLE'

2»S SALUE ^ 2 ^ ISLANDS 100 \ULABESl

North Banda Sea

TS

r s o South

s SP 3000 2500 2000 1500 1000 500 0 ophlolitic basem ent

carbonate ' . y ' basem ent highplatform

negative Gorontalo Basin flower structure 10 km

Figure 6.11 Location of gravity profile across the shelf region west of Taliabu, showing the approximate position of seismic line QS-1 and its line drawings interpretation.

165 40 0 Ü 200 E > 2 -200 ü -4 0 0

South North Banda Sea IV es/ Taliabu Shelf South Molucca Sea North 0 F - 1 . 6 4 ___ —- 10 .c 0.0 Q. (U 2 0 a 3 0 -200 -100 100 200 Distance (Km)

4 0 0 (0 200 CDE

2 -200 ü -4 0 0

South North Banda Sea IVesC Taliabu Shelf South Molucca Sea North 0 F -1.64 — ------1:64 ------& 10 0 .0

CL 03 2 0 Û 0.4 3 0 -200 -100 100 200 Distance (Km) V .E. = 2

KEY: Observed gravity Computed gravity (2-D) tectonic mélange -1.64 0.0 0.4 0.1 -0.27 -0.47 Reef seawater Sula upper mantle oceanic crust sediments continental North Banda Sea North Banda Sea arc-voicanics 0.05 fragment Molucca Sea South Molucca Sea SW-Arm Halmahera Generated with GM-SYS TM

Figure 6.12a and 6.12b An early stage crustal models beneath the shelf region west of Taliabu, showing (a) the gravitational effects of the water layer of the North Banda Sea and the South Molucca Sea, and (b) the computed free-air gravity was brought into the level of the observation by setting the Moho at about 20 km below sea level.

166 400 m CD 200 E

Î -200 CD -4 00

South North Banda Sea IVesf Taliabu Shelf South Molucca Sea North . 0 "f -1.64 10 0.0 -c Q. (U 20 Q 0.4 30 -200 -100 100 200 Distance (Km)

40 0 O 200 E Z' 1 -200 CD -400

SouthNorth Banda Sea IVesf Taliabu Shelf South Molucca Sea North 0 -1.64 -0.27; -1.64- 0.1 10 0.0 20 0.4 30 -200 -100 100 2000 Distance (Km) V.E. = 2

KEY: Observed gravity Computed gravity (2~D) tectonic mélange -1.64 0.0 0.4 0.1 -0.27 -0.47 Reef seawater Sula upper mantle oceanic crust sediments continental North Banda Sea North Banda Sea arc-volcanics 0.05 fragment Molucca Sea South Molucca Sea SW-Arm Halmahera Generated with GM-SYS

Figure 6.12c and 6.12d (c) The average level of free-air gravity requires the Moho at about 11 km in the North Banda Sea region, (d) Introduction of a sedimentary layer and arching geometry of non­ standard oceanic crust in the North Banda Sea region improve the agreement between model and observation. 167 400 O 200 E •f' 2 -200 CD -4 0 0

South North Banda Sea West Taliabu Shelf South Molucca Sea North 0 F -1.64 -1.64 0.0 ■0.47 10 0.1 -c Q. 0.1

4 0 0 1

CD 2 0 0 - E 0 -

2 -2 0 0 - CD -4 0 0 -

South North Banda Sea W est Taliabu Shelf South Molucca Sea North 0 -1.64 -0.27 -1.64 -0.47 10 0.0 0.05 0.1 20 0.4 3 0 -200 -100 0 100 200 Distance (Km) V .E. = 2

KEY: Observed gravity Computed gravity (2-D) tectonic mélange -1.64 0.0 0.4 0.1 -0.27 -0.47 Reef seawater Sula upper mantle oceanic crust sediments continental North Banda Sea North Banda Sea arc-volcanics 0.05 fragment Molucca Sea South Molucca Sea SW-Arm Halmahera Generated with GM-SYS 7U

Figure 6.12e and 6.12f (e) Introduction of about 10 km thick tectonic mélange underlain by standard oceanic crust produces good agreement between model and observation in the Southern Molucca Sea region, (f) Thiiming the mélange and introducing arc-volcanics in the northern part of the section significantly improve the match to the observed free-air gravity in this region. 168 400 <3 200

î -200 • Ü -4 00

South North Banda Sea W est Taliabu Shelf South Molucca Sea North 0 4)27 -1.64 ■0.47 10 0.0 0.05 0.1 20 0.4 30 -200 -100 0 100 200 Distance (Km)

4 0 0 1 s 20 0 - E 0 -

P -2 00 - o -4 0 0 -

South North Banda Sea W est Taliabu Shelf South Molucca Sea North -1.64 -0 .2 7— •■0.47 ■0.27 -1.64 0.1 0.05 0.0 0.1 20 0.4 -200 -100 0 100 200 Distance (Km) V.E. = 2

KEY: Observed gravity Computed gravity (2-D) tectonic mélange -1.64 0.0 0.4 0.1 -0.27 -0.47 Reef seawater Sula upper mantle oceanic crust sediments continental North Banda Sea North Banda Sea arc-volcanics 0.05 fragment Molucca Sea South Molucca Sea SW-Arm Halmahera Generated with GM-SYS TM

Figure 6.12g and 6.12h (g) Introduction of crustal block which represents carbonate platform (density contrast - 0.27 Mg.m’^) minimises the disagreement between model and observation in the northern flank of the gravity high, (h) The match to the observation was further improved by adding crustal block with a density contrast -0.47 Mg.m'^, representing reef build-up resting on top of the platform. 169 400 gravity e ffe c t o f se a w a te r =. 200 I . t tS -200

-400 400 gravity effect of upper mantle 200

-200

-400 400 gravity effect of oceanic crust 200 - 0 - -200 -

-400 400 gravity effect of tectonic mélange => 200 i . OC -200 -400 400 gravity effect of sediments 200

-200

-400 400 gravity effect o f arc-volcanics 200 - 0 - -200

-400 400 overall gravity effect o f crustal model shelf region west Taliabu c 200 t 0 C3C -200

shelf region South North Banda See wesi Taliabu South Molucca Sea North .-0.47, 0 -f.6 4 ■0.27 ■0.27 • .-1.64. ■0.47 10 0.05 0.0 0.1 20 0.4

30 •200 -1000 100 200 Distance (Km) V.E. = 2

KEY: Observed gravity Computed gravity (2-D) tectonic mélange -1.64 -0 .2 7 -0 .4 7 0.0 0.4 0.1 R e e f seawater Sula upper mantle oceanic crust sediments continental North Banda Sea North Banda Sea arc-volcanics 0.05 fra g m en t Molucca Sea South Molucca Sea SW-Ann Halmahera Generated with GM-SYS

Figure 6.13 One possible structure of the crust beneath the shelf region west Taliabu, showing the individual as well as overall gravitational effects of the crustal layers.

170 GULF OF t TOMINI Poh Head MOLUCCA

ARM

SULAWESI

Tanjung UngkotHJ

summsi

GULF BONE Tom orl B asin Manui KEY: ' BtlhynMry

W owoni Kilometres SWMS SoulttwK>l»m ptilol the Uotuooe See Stmt Suk Thnat (?l BOCFBenooeiconlineieellreomenl SS3f Stx/n Sule-Sorong Feel

1-7 ------1 GULF OF TOMINI MOLUCCA am Sorong ^ O _ KepalaBurvng t t ,. ' IRIAN JAYA O^F % ^ g SULA WES MIsool TOLO ^

BANDA SEA .II^E ,122°E^Ç) ,124‘E______^I2S‘E i3œE ,132°E

Figure 6.14 Line of gravity profile across the Banggai Islands region, showing (a) gravity and (b) bathymetry and sedimentary isopach maps which were used to provide some degree of constraint on the analysis of crustal models in the region.

171 400 g 200-1 & -200— OI -4 0 0

Tomori Basin Banggai Islands South Molucca Sea NE

0- -1.64 0.0 10- 20-

0 100 200 3 0 0 V .E . = 2 Distance (Km)

40 0 ro 200- — 0- -200- Of -4 0 0

SW Basin Banggai IslandsTomori South Molucca Sea NE

0- -1.64 0.0 10- 20- 0.4

0 100 200 3 00 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.15a and 6.15b Preliminary crustal models beneath the Banggai Islands region, showing (a) the gravitational effects of the water layer of the North Banda Sea and the Southern Molucca Sea. (b) The general level of the observed free-air gravity requires the Moho at about 20 km below sea level.

172 400 g 200- “ 0- ■200— Of -4 0 0

SW North Banda Sea W est Taliabu Shelf South Molucca Sea NE 0- -1.64 -0.47 10- 0.0 20- È 0.4

0 100 200 300 V.E. = 2 Distance (Km)

4 0 0 g 200-1

■200 — Oï -4 0 0

North Banda Sea West Taliabu Shelf South Molucca Sea NE 0- -1.64 -0.47 10- 0.0 20- 0.4

3 0 0 100 200 3 00 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.15c and 6.15d (c) Gravitational effects of the introduction of about 13 km thick low-density tectonic mélange beneath South Molucca Sea and (d) the additional effects of the oceanic crust of standard thickness.

173 400

-200 — OI -4 0 0

SW Basin Banggai IslandsTomori South Molucca Sea NE 0- -1.64 ■0.47 10- 0.0 20- 0.4

0 100 200 30 0 V .E . = 2 Distance (Km)

4 0 0 « 200-1

-200 — aI -4 0 0

SW Tomori Basin Banggai Islands South Molucca Sea NE 0- -1.64 -0.47 10- 0.0 0.1 20- 0.4

0 100 200 3 0 0 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.15a and 6.15f (e) Raising the Moho and hence slightly thinning the mélange produces good match in the South Molucca Sea region, (f) Adjustments to the geometry of the mélange wedge appear to produce an acceptable level of match between model and observation in the northern half of the profile.

174 400

200 -

- 200 -

SkV Tomori Basin Banggai Islands South Molucca Sea 0 - -1.64 -0.47 : 1 0 - ■C - S' 2 0 - U

3 0 - 0 100 200 3 0 0 V .E . - 2 Distance (Km)

4 0 0 -

2 0 0 - h 1 E. 0 — 1 ' 2 -2 0 0 — a -4 0 0 -

SW Tomori Basin Banggai Islands South Molucca Sea NE 0 - -0.47 Î 1 0 - 4= - S' 2 0 - o

3 0 - 0 100 200 3 0 0 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.15g and 6.15h (g) Alternative adjustments to the Moho produce the same effects as in Fig. 6.15f but are probably geologically less plausible, (h) Resetting the geometry of the Moho and mélange wedge maintain the level of the match but introducing sediments of the Tomori Basin appears to degrades the agreement between model and observation in the southern half of the profile.

175 400

m 2 0 0 -

" 0 - Of - 200 — -4 0 0

Tomori Basin Banggai Islands South Molucca Sea NE 0 - ■1.64 -0.37 -0.47 0.1 1 0 - 0.0 0.1

2 0 - 0.4

0 100 200 3 0 0 V.E. = 2 Distance (Km)

4 00

« 200 - 0-: Of - 200 - -4 0 0

SW Tomori BasinBanggai Islands South Molucca Sea NE 0 - -1.64 -0.37 -0.47 1 0 - 0.1 0.0 0.1

20 - 0.4

0100 200 3 0 0 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.151 and 6.15J (i) Introduction of standard oceanic crust beneath the Tomori Basin produces too high a level of 6 ee-air gravity in the southern part of the profile, (j) Oceanic crust has to be thickened to about 14 km to produce the required level of observed gravity.

176 400 200- 0- 5 -200—

-4 0 0

SW Basin Banggai IslandsTomori South Molucca Sea NE 0- -1.64 ■0.37 ■0.47 10- 0.0 0.0 0.1 Q. 20- 0.4

0 100 200 30 0 V .E . - 2 Distance (Km)

4 0 0

200- 0- 2 -200 —

-4 0 0

SIV Tomori Basin Banggai Islands South Molucca Sea NE 0- -1.64 -0.37 .47 10- 0.0 0.1 Q. 20- 0.4

0 100 200 30 0 V.E. = 2 Distance (Km)

KEY: # observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.15k and 6.151 (k) Introduction of about 11 km thick continental fragment beneath the Tomori Basin produces the level of the observed free-air gravity in the region. (1) Effects of adjustments of the geometry of the continental fragment.

177 400 200- 0- 2 -200—

-4 0 0

SW Tomori Basin Banggai islands South Molucca Sea NE 0- -1.64 ■0.37 -0.47 10- 0.0 0.1 20- 0.4

0 100 200 3 00 V .E . = 2 Distance (Km)

4 0 0

-200- O1 -4 0 0

Tomori Basin Banggai Islands South Molucca Sea NE 0- -1.64 -0.37 -0.47 10- 0.0 0.1 20- 0.4

0100 200 300 V .E . = 2 Distance (Km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 -0.47 -0.37

sea water Banggai upper mantle oceanic crust Molucca Sea Tomori Basin continental fragment tectonic melange sediments

Generated with GM-SYS

Figure 6.15m and 6.15n Varieties of crustal structures of the Banggai Islands region which satisfy the observed gravity field, (m) A model with simpler geometry and (n) a more complex one.

178 400 Gravity effect of sea water 200 - 0 - -200 -

-4 0 0

4 0 0 Gravity effect of the upper mantle 200 - 0 - O -200 - -4 0 0

4 0 0 Gravity effect of the oceanic crusts 200 - 0 - O -200 - -4 0 0

4 0 0 Gravity effect of the Molucca Sea tectonic melange 200 - I 0 - OÎ -200 - -4 0 0

4 0 0 Gravity effect of the North Banda Sea sediments 200 - 0 - -200 -

-4 0 0

400 overall gravity effects of crustal structure Banggai Islands 200 I ÜI -200 -400

Tomori SW North Banda Sea Basin NSSF Banggai Islands South Molucca Sea NE -1.64 .64 ■0.37 -0.47 10 - 0.0 0.1

20 - 0.4

0 100 200 30 0 V .E . = 2 Distance (km)

KEY: Observed gravity Computed gravity (2-D) Computed gravity(214-D)

-1.64 0.0 0.4 0.1 -0.37 ■C.47

seawater Banggai upper mantle oceanic crust sediments tectonic mélange Continental North Banda Sea Tomori Basin Molucca Sea Fragment Molucca Sea NSSF = North Sula-Sorong Fault

Figure 6.16 One possible crustal model of the Banggai Islands region, showing the individual as well as overall gravitational effects of the crustal layers. The 2/4-D response of the model was evaluated in view of the limitation on the strike extent of the section in the west-northwest direction towards the East Arm Sulawesi {cf Fig. 6.14). 179 HALMAHERA

BACAN \ \ a r m

MOO NNE

1°S NNE

OBI \100

LS-S2 Basin

LS-S1 SERAM SEA SSE 100 100 SSW

/ i2æE, SSW

SSW KOlUCCA-StMOMC NNE

LS-S1

SSE NNW

LS-S2

GULF OF TOMINI MOLUCCA seA

GULF 6 ^. SULAWESI TOLO

SEA

B A N D A S E A

Figure 6.17 Line of gravity profile across Obi, showing the interpreted seism ic lines (Letouzey et al. 1 9 8 3 ) which provide som e degree of control on the analysis of crustal structure in this region. 180 400 200 - 0 - -200 - ^00

N NESeram Sea Obi Island Obi Strait NNESeram

-t.64 0 - -1.64 10 - 0.0

20 -

i t n e ( m VE. = 2 -100 0 100 Distance (km)V.E

4 0 0 200 - 0 - -200 -

-4 0 0

N SWSeram Sea Obi Island Obi Strait NNESSW -1.64 0 - -1.64 10 - 0.0

20 - 0.4

100 i t n e k ). . = 2 -100 0 Distance (km)V.E

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 0.05 -0.37 sediments tectonic sea water continental fragment upper mantle oceanic crust arc-volcanic -0.47 south Obi SW-Arm Halmahera melange

Generated with GM-SYS

Figure 6.18a and 6.18b (a) Gravitational effects of the water layer in the Seram Sea and the Obi Strait may be compensated by (b) raising the Moho to approximately 20 km below sea level. 181 200 -

o -200 -

SSW Seram Sea Obi Island Obi Strait NNE — -t.64 0 - -1.64 10 - 0.0

20 - 0.4

0 100 V .E . = 2 -100 Distance (km)

200 -

O -200 -

SStV SeramSea Obi Island Obi Strait NNE 0 - -1.64 -1.64 10 - 0.0

20 - 0.4

itn e(mVE. = 2 -100 0 100 Distance (km)V.E

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 0.05 ■0.37 sediments tectonic sea water continental fragment upper mantle oceanic crust arc-volcanic -0.47 south Obi SW-Arm Halmahera melange

Generated with GM-SYS

Figure 6.18c and 6.18d (c) Depressing the Moho beneath Obi appears to minimise the mismatch at both ends of the profile but does not explain the local high in the centre, (d) The introduction of a 3 km thick high density ultramafic block seems to produce an acceptable match between model and observation. 182 400 200 - I ô -200 - -4 0 0

SSIV Seram Sea Obi Island Obi Strait NNE

-t.64 0 - -1.64 0.1 10 - 20 - 0.0 0.4 3 0 -100 0 100 itn e k VE. - 2 Distance (km )V.E

40 0 5 200 - 0 - ot -200 - -4 0 0

SSIV Seram Sea Obi Island Obi Strait NNE

-1.64 10 - 0.1 20 - 0.0 0.4 -100 V .E . = 2 0 100 Distance (km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 0.05 -0.37 sediments

sea water continental fragment upper mantle oceanic crust arc-volcanic tectonic south OtH SW-Arm Halmahera -0.47 melange

Generated with GM-SYS

Figure 6.18e and 6.18f (e) Approximately 15 km of basic rock is required to closely matched the observed gravity field but (f) inclusion of a thin ultramafic sheet in place of some of these rocks appears to produce the required match.

183 400

200 -

(Df -200 -

Seram Sea Obi Island Obi SlraH NNE -1.64-

I -0.37 10 - 0.0 0.1 I 20 - 0.4

-1000 100 V.E. - 2 Distance (km)

200 -

f 200 -

Seram Sea Obi Island Obi Strait NNE

-1.64 I -0.37 10 - 0.0 0.1 0.05

20 - 0.4

-100 0 100 V.E. = 2 Distance (km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 0.05 -0.37 sediments tectonic sea water continental fragment upper mantle oceanic crust arc-volcanic -0.47 south Obi SW-Arm Halmahera melange

Generated with GM-SYS

Figure 6.18g and 6.18h (g) Modification to the crustal section illustrated in Fig. 6.18f, showing the northward continuation of oceanic material exposed on Obi. (h) The increases in the gravity field towards the northern end of the profile appears to demand a relatively high density block, representing the arc-volcanic terrane of the West Halmahera-Tamrau. 184 400

200 -

0 -

-200 - ^ 0

Seram Sea Obi Island Obi Strait NNE

0 - -1.64 -1.64 ■0.37 10 - 0.05 0.0 0.1

20 - 0.4

-100 0 100 V.E . = 2 Distance (km)

4 0 0

200 -

0 -

-200 -

-4 0 0

SSIV Seram Sea Island Obi StraitOt)l NNE

0 - -1.64 -0.37_ ■0.37 10 - 0.05 0.0 0.1

20 - 0.4

-100 0 100 V .E . = 2 Distance (km)

KEY: • observed gravity ^ computed gravity

-1.64 0.0 0.4 0.1 0.05 ■0.37 sediments tectonic sea water continental fragment upper mantle oceanic crust arc-volcanic ■0.47 south Obi SW-Arm Halmahera melange

Generated with GM-SYS

Figure 6.18i and 6,18j (i) Adjustments to the geometry of the dipping basaltic layer produce a better level of match but (j) the introduction of a sedimentary layer in the south degrades the agreement between the model and observation.

185 400

200 -

0 -

-200 - ^00

Seram Sea Obi Island Obi Strait NNE

-1.64 -1.64 Ut ■0.37 10 - 0.05 0.0 0.1

20 - 0.4

-100 0 100 V .E . - 2 Distance (km)

4 0 0

200 -

0 -

-200 -

-4 0 0

SSIV Seram Sea Obi Island Obi Strait NNE

0 - -1.64 -1.64 -0.37. -0.37

10 - 0.1 0.05 0.0

20 - 0.4

-100 0 100 V.E. = 2 Distance (km)

KEY: observed gravity computed gravity

-1.64 0.0 0.4 0.1 0.05 -0.37 sediments tectonic sea water continental fragment upper mantle oceanic crust arc-volcanic -0.47 south Obi SW-Arm Halmahera melange

Generated with GM-SYS

Figure 6.18k and 6.181 (k) Thinning of the standard crust in the southern part of the section appears to improve the level of the match. (1) Although fair agreement is achieved by further thiiming, this crust is unacceptably thin.

186 200 -

-200 -

SSIV Seram SeaObi Island Obi Strait NNE

-1.64 137, E -0.37 0.1 S 10 - 0.1 0.05 0.0

20 - 0.4

-100 0 100 V.E. - 2 Distance (km)

ü

SSW Seram Sea Island Obi StraitObi NNE

-1.64 137, 1 -0.37 0.1 10 - 0.1 0.05 §• 0.0 Q 20 - 0.4

-100 V.E. - 20 100 Distance (km)

1 OI

Seram SeaObi Island Obi Strait NNE 0 - -1.64 I ■0.37, -0.47 0.1 10 - 0.1 0.05 0.0

20 - 0.4

-100 V.E. = 20 100 Distance (km)

KEY: • observed gravity computed gravity

-1.64 0.0 0.4 0.1 0.05 -0.37 sediments tectonic s e a water continental fragment upper mantle oceanic crust arc-volcanic -0.47 south Ot}i SW-Arm Halmahera melange

Generated with GM-SYS Figure 6.18m, 6.18a and 6 .I80 (m) The introduction of standard oceanic crust appears to produce the required level of the observed free-air gravity in the southern part of the profile, (n) adjustments to the geometry of the continental fragment improve the level of agreement between the model and the observation, (o) Alternative crustal model with a low-density tectonic mélange overlying the oceanic fragment beneath Obi Strait.

187 400 Gravity effect of seawater

200 -

-200 -

-4 0 0

4 0 0 Gravity effect of tfie upper mantle 200 - -****-

0 -

-200 -

-4 0 0

4 0 0 Gravity effect of the oceanic crusts

200 -

0 -

O -200 - -4 0 0

4 0 0 Gravity effect of the Seram Sea sediments 200 - ...... •N. 0 - O -200 -4 0 0

4 0 0 Gravity effect of the Obi Strait sediments I 200 0 -

(DI -200 - -4 0 0

4 0 0 overall gravity effect of crustal structure Obi region 200

t -200 CD -4 0 0

SSW MSF NNE Seram Sea Obi Island Obi Strait 0 - -1.64 -0.37 0.1 0.1 10 - 0.0 0.05

20 - 0.4

-100 0 100 V .E . = 2 Distance (km)

KEY: Observed gravity # Computed gravity (2-D) Computed gravity(2yi-D) ^ tectonic mélange 0.1 0.05 -1.64- 0.0 0.4 -0.47 Molucca Sea seawater South Obi upper mantle oceanic crust arc-volcanics Continental Seram Sea SW-Arm ■0.37 sediments Fragment Molucca Sea (remnant?) Halmahera

SSF = Sula-Sorong Fault MSF = Molucca-Sorong Fault Generated with GM-S YS ™

Figure 6.19 One possible crustal model of Obi region, showing the individual as well as overall gravitational effects of the crustal layers. The 214-0 response of the model was evaluated in view of the limitation on the strike extent of the section in the northwest direction towards the Molucca Sea {cf. Fig. 6.17). 188 Chapter 7 CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDIES

Along the zone of the Sorong Fault system in the region of the Sula Islands, the structure of the crust is essentially characterised by the presence of attenuated continental fragments juxtaposed against the oceanic crust of the Southern Molucca Sea in the north and the North Banda Sea in the south. The continental fragments appear to be very thin (about 10 km or less) in the region of the eastern Sula Islands but become thicker towards the west (about 18 km beneath the western Taliabu Island and approximately 22 km beneath the Banggai Islands). The continental fragments also appear to be very limited in width (about 20 km or less) in the region of the eastern Sula Islands, 50 km in Taliabu and about 100 km in the region of the Banggai Islands. The thickening and widening of the continental fragments (the Banggai Sula Continental Fragment) were probably due to the collision between the fragments and the East Sulawesi terrane. One of the conclusions which may be drawn is that continental terranes transported by major strike slip faults may be not merely small in area but may have very limited extent in depth as well. The lack of deep root may be explained by slicing away of parts of the lower crust in extensional or more probably in compressional flower structures.

The moderate bathymetric depth, the commonly thick tectonic mélange and therefore the deeply seated oceanic crust in the Southern Molucca Sea region north of the Sula Group and the Banggai Islands suggest that the region has been undergoing subsidence. The subduction of the Molucca Sea lithospheric plate beneath the Sangihe and Halmahera Arcs has been thought to have been the primary driving mechanism of the subsidence. Although the precise rate of subsidence is not presently known, it is probably rapid. The three gravity models analysed in the Sula Group and the Banggai Islands all show that the continental crust in this region appears to dip northwards. This probably in response to the sinking of the Molucca Sea lithosphere.

189 The generally deep sea, thin sediments and anomalously thin oceanic crust in the North Banda Sea region south of the Sula Islands may be the indication of regional crustal doming. This phenomenon may have resulted from the interaction between the tectonic elements in this region including the South Sula-Sorong Fault system north of the North Banda Sea, the West Bum Fracture east of the North Banda Sea and the relatively stationary landmass of Sulawesi in the west. The exact mechanism of the cmstal doming is not presently known but presumably differential tectonic stress associated with the movements on the various fault systems have caused this phenomenon. Another possibility for the contributing mechanism is the subsidence in the Molucca Sea region. The subsidence may have produced bending forces and have initiated flexures which propagate through the surrounding region. Depending on the flexural rigidity of the cmstal layers, bending and fracturing of the cmst may have occurred.

One result of the study indicates that the Sula Thmst north of the Banggai-Sula Platform previously recognised by Silver et al. (1983), could not be identified on the seismic section examined in this study. Instead, a drowning carbonate platform which forms a prominent feature near the southern flank of a negative flower stmcture {cf. Figs. 5.4, 5.6 and 6.13). On the basis of similarity of seismic images which were previously interpreted as thmst stmctures {of. Fig. 5.5), these may in fact a drowning carbonate platform situated close to the southern edge of a negative flower stmcture. This may imply that along the northern side of Sula Islands is the region of growth and subsidence of carbonate rocks.

In the Obi region, the stmcture of the cmst is characterised by the presence of ophiolitic rocks in the north and a block of continental fragment in the south. The ophiolitic rocks may have originated in the Philippine Sea Plate. The continental fragment appears to be similar to the continental cmst which underlain the Kepala Burung region and is juxtaposed against oceanic cmst, possibly of Philippine Sea origin. The ophiolitic rocks on Obi have been interpreted as the result of emplacement by an obduction along a high angle thmst fault which separates the continental block in the south from the oceanic material in the north. Recent seismicity on Obi indicated

190 movements of normal faults which resulted from an east-west movement of the Molucca-Sorong Fault (pers. comm. Ismet Effendi GRDC, 1996). Transtensional kinematics of the Molucca-Sorong Fault may have been the mechanism which produced the extensional faulting in the region.

The high level Bouguer gravity values along the exposed continental rocks of the Sorong Fault Zone should be attributed to the elevated Moho rather than to the existence of the continental fragments. This may in turn, produced high heat flow along the zone, promoting thermal maturation in areas where hydrocarbon potential are likely to occur such as along the northern side of the Sula Island Group.

Although the present study has presented results which appear to be geologically plausible, there are a number of uncertainties to be resolved. Further studies which may substantiate this work in the region might include seismic imaging, heat-flow measurements, magnetics and field geology. Utilization of the latest satellite gravity and aeromagnetic data would significantly improve results of this work.

191 REFERENCES

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F itc h , T.J. 1970. Earthquake mechanism and island-arc tectonics in the Indonesian- Philippine region. Bull. Seis. Soc. Amer., 60: 565-591.

F o w le r , C.M.R. 1990. The solid Earth - an introduction to global geophysics. Cambridge University Press.

F u r u m o to , A.S., Hussong, D.M., Campbell, J.F., Sutton, G.H., M a la h o f f , A., Rose, J.C. AND W oolard, G.P. 1970. Crustal and upper mantle o f the Solomon Islands as revealed by seismic refraction surveys ofNovember-December 1996. Pac. Sci. 24(3), 315-332.

G a r r a r d , R.A., Supandjono, J.B. and Surono 1988. The geology o f the Banggai- Sula Microcontinent, Eastern Indonesia. Proceedings Indonesian Petroleum Association, 17th Annual Convention, October 1988,24-51.

G o o l, M. van, Husson, W.J. and Prawirasasra, R. 1987. Heat flow and seismic observations in the northwestern Banda Arc. Journal of Geophysical Research, Vol. 92, 2581-2586.

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199 Appendix A

Gravity anomalies in the Talaud Island Group, Central Molucca Sea

Sardjono and John Milsom Research School of Geological and Geophysical Sciences Birkbeck College and University College London Gower St., London WC1E 6BT, UK

ABSTRACT The Talaud Islands lie midway between the opposed Halmahera and Sangihe arcs in the Molucca Sea collision zone of eastern Indonesia. The basement rocks of the islands, which include mafic and ultramafic intrusives and extrusives, have been variously regarded as either samples of one of the colliding accretionary wedges or as upthrust fragments of the underlying Molucca Sea oceanic plate elevated to sea level in the course of collision. Gravity readings on the islands have now completed the picture provided by earlier marine surveys and have defined local highs in the southern part of the group which can be interpreted as parts of a single feature disrupted by strike-slip faulting. The highest fields are associated with and probably produced by mafic and ultramafic rocks but the overall level of Bouguer anomaly does not suggest that the bulk of the Talaud Rise is made up of such material. The oceanic rocks are therefore considered to be slices of oceanic crust incorporated into an accretionary complex during the normal processes of subduction and not parts of coherent block uplifted as a direct consequence of collision.

convergence and the collision drive must therefore be (7 V ' provided mainly by plate motions occurring elsewhere.

I

J J 2°30'N A: 120 E IM C 130't 120-6 123 6 130 6 120 6 123"6 130 6 Figure 2. Benioff Zones beneath the Molucca Sea. Each frame represents a one degree slice of latitude with centre coordinates as shown (V.E.=1). Data source the National Geophysical and Solar Terrestrial Data Center, NOAA, Boulder, Colorado. ' -'"A., 7 . ^ TV

Figure 1. Simplified tectonic map of eastern Indonesia and surrounds, showing the location of the Talaud Islands study area.

INTRODUCTION The Molucca Sea, in north-eastern Indonesia (Fig. 1), has attracted considerable geological interest as being the only present-day example of active arc-arc collision. A possibly similar situation in the vbfticc. s « 2 (Papua New Guinea) may not be an exact analogue since there may currently be no subduction along the southern margin of the sea {cf. Silver ei a i, 1991) and it is even possible that subduction has altered from the northern to the southern margin through time. In the Molucca Sea, on the other hand, subduction to both east and west is attested by well defined Benioff Zones and present-day !r' volcanic activity. Collision of this type can be expected to be rare since neither slab-pull nor ridge-push from the Figure 3. Bathymetry of the Molucca Sea, after Moore intervening oceanic plate can play any part in maintaining and Silver (1983).

2 0 0 TALAUD ISLAND

rc

TALAUD ISLANDS

a

f

127-El 128-E I

Coastal gravity station r ® Marine geophysical survey track 0 Bathymetry contour line (km) ^ Gravity anomaly contour line (mGal) ^ Thrust Fauit Active Subduction Zone

■iiri ^ t_ .*irt

Figure 4. (aj. Bathymetry contour map around Talaud Islands. Contour interval is 500 m, after Moore and Silver (1983). (bj. Gravity anomaly in the northern Molucca Sea. Contour values, in milligals, are of free-air anomaly offshore and of Bouguer anomaly onshore. Free- air anomaly contour after Moore and Silver (1983).

The Molucca Sea as it is today trends roughly N-S southern part of the sea coincides with a remarkably deep and is some 200 km wide. It must formerly have been at free-air gravity low which is commonly attributed to the least 1000 km wide since the opposing Benioff Zones dip presence of a very thick layer of low density tectonic at angles of about 60°, to a depth of more than 200 km melange, representing material scrapped from the upper beneath Halmahera in the east and to more than 500 km surface of the subducting plate at the two subduction beneath the Sangihe Island to the west (Fig. 2). The zones. The two accretionary complexes appear to have

201 now met and amalgamated, since 200 km distance across GRAVITY DATA the sea is no greater than the distances commonly Gravity information has been collected on a observed to separate active, non-collided subduction considerable number of research cruises in the Molucca traces from their corresponding volcanic arcs. Thrust Sea (cf. Moore and Silver 1983). More recently, gravity controlling the formation of linear throughs at the reading have been taken along the coast of the Talaud margins of the sea dip away from, rather than towards the Islands as a part of the Sorong Fault Zone Project, a adjacent volcanic arcs; the surface trace of Sangihe Arc collaboration between the Geological Research and subduction lies off Halmahera and the surface trace of Development Centre, Bandung, and the University of Halmahera subduction is close to the Sangihe Islands London. In the course of this programme, geological, (Silver and Moore 1978; McCaffrey et al., 1980; palaeomagnetic and gravity observations have been made McCaffrey 1982; Moore and Silver 1983). on the islands east of the Molucca Sea, as well as on the smaller islands at its centre. The gravity contours in Figure 4b have been prepared by combining part of free- air anomaly map presented by Moore and Silver (1983), which summarised the offshore data, with results, shown in more detail in Figure 5, from the Talaud Islands themselves. All readings taken on the islands were located at or close to sea level and latitude-corrected values at reading points can therefore be regarded as both Bouguer and free-air anomalies. However, the contours in Figure 5 have been drawn across the islands without incorporating a positive bias in regions of high elevation and are therefore of Bouguer anomaly. The extreme irregularity of the coastlines and the generally small width of the islands have allowed these contours to be interpolated between coasts with considerable confidence; TALAUD ISLANDS in many cases the coast to coast distance is little more than the average distance between adjacent data points along the coast.

DISCUSSION Bouguer anomaly levels on Talaud are generally high, averaging about +120 mGal and with a minimum in the region of +80 mGal. The highest values were recorded in the south, on Kabaruan and southern Karakelang, from where there is a general and roughly __ linear decrease northwards. The high gravity values coincide with regions in which basic and ultrabasic rocks Figure 5. Gravity anomalies in the Talaud islands. All have been mapped in outcrop. The gravity contour pattern stations are at or very close to sea-level and the map would be considerably simplified were Kabaruan and thus independent of the reduction density. Salebabu, and their associated gravity field, to be moved about 15 km northwest along a fault through the Lining Strait. Not only is the existence of such a fault indicated The central part of the Molucca Sea is relatively by gravitational and topographic features, but it would shallow (Fig. 3) and, although there is no continuous form a natural member of a set, strongly suggested by ridge, a number of islands rise above sea level. Mayu and coastline alignments, of conjugate NE-SW and NW-SE Tifore, in the south, are both very small (less than 10 km fractures formed in response to E-W directed collision across) but in the northern part of the sea the islands of stress. Contours in the northern part of Karakelang, the Talaud group form a more considerable land mass however, are most easily drawn with a pronounced east- (Fig. 4a), measuring almost 100 km from north to south west trend (Fig. 5). although only about 20 km from east to west across the widest part of Karakelang, the largest island. Basement Free-air and Bouguer anomaly values in the Talaud rocks in the Talaud group, as on Mayu and Tifore, group are some 200 mGal higher on average than free-air consist of a variety of lithologies of generally oceanic values over the adjacent regions of deeper water which affinity which have been widely regarded as providing mark the northern extensions of the Sangihe and samples of the collision complex (cf. Moore and Silver Halmahera Throughs. As the model studies in Figure 6 1983). There is however, ambiguity in some of the demonstrates, a considerable part this difference can be published discussion as to whether the islands are being attributed to the presence of the low-density water seen as uplifted but otherwise little modified portions of column, and indeed this effect alone is sufficient to one, or both, of the accretionary prisms formed during account for the whole of the difference in the northern the period of simple oceanic subduction or slices of part of Karakelang. Along the modelled profile, which Molucca Sea crust which have been thrust into the cuts across Salebabu Island, there are certainly effects overlying collision complex as a consequence of due to sources beneath the seabed, but the differences collision. The later view has recently been strongly between the observed and calculated free-air profiles are argued, in relation to Mayu and Tifore at least, by not such as to suggest that the rocks exposed on the McCaffrey (1991). islands are very different from the adjacent, submerged.

2 0 2 parts of the collision complex. The water-layer effect has such a slice should have been selected fro elevation as been modelled using a density contrast of 1.37 Mg.m \ part of the Talaud Islands by chance alone. As an equivalent to ascribing a bulk density of 2.4 Mg.m'^ to alternative we would suggest that the relative rigidity of the bathymetric high. Such a density is certainly not an ophiolite slice within the forearc complex might have consistent with the high being underlain mainly by contributed to the preservation and uplift of a coherent uplifted but otherwise largely unmodified oceanic block during the collision between the converging forearc basement. wedges.

ACKNOWLEDGMENTS The gravity survey on the Talaud Islands was carried out as part of the University of London - Geological Research and Development Centre Sorong Fault Zone Project, and was funded by a grant from the University M«asur»d free m* mmomafy Computed eflect o* water layer ortfy of London Consortium for Geological Research in Southeast Asia. Sardjono publishes with the permission Talaud of the Director, Geological Research and Development Centre, GRDC-Bandung, Indonesia. This paper is Distance (km) contribution No. of the Birkbeck College and Figure 6. Free-air gravity profile, computed gravity University College London Research School of profile and bathymetry cross section, for an E-W Geological and Geophysical Sciences, Gower Street transect passing across Salebabu Island. Values along London W CIE 6BT, UK. the computed profile have been arbitrarily increased by a constant amount to produce maximum coincidence REFERENCES CITED with the observed profile. Computations are based on Bernstein-Taylor, B.L., Brown, K.M., Silver, E.A., and a density contrast of 1.37 Mg.m'® between the sea water and the rocks beneath the sea bed, corresponding to Kirchoff-Stein, K.S., 1992, Basement slivers within rock density of 2.4 Mg.m ®. Note that this relatively low the New Britain accretionary wedge; implication for density is sufficient to produce the observed amplitude the emplacement of some ophiolitic slivers: of the central Molucca Sea high. Tectonics 11, p. 753-765. Marzuki, S., Mimanda, E., and Ahmad, 1990, Bouguer An explanation is certainly required for the higher anomaly map of Pagai and Sipora quadrangles, Bouguer anomalies in the southern Karakelang and Sumatra (1:250,000): Geol. Res. Develop. Centre, Kabaruan. but even there the gravity relief is no greater Bandung. than has been recorded in some forearc regions which McCaffrey, R., 1982, Lithospheric deformation within the have not been involved in collision. Recent multichannel Molucca Sea arc-arc collision: evidence from seismic reflection studies in the Solomon Sea have shallow and intermediate earthquake activity: Journ. defined coherent reflections from within a part of the Geophys. Res. 87, p. 3663-3678. accretionary complex south of New Britain which have McCaffrey, R., 1991, Earthquakes and ophiolite been interpreted as marking the location of a slab of emplacement in the Molucca Sea collision zone: ocean floor incorporated into this now approaching Tectonics 10, p. 433-453. collision (Bernstein-Taylor et al., 1992). It is easy to McCaffrey, R., Silver, E.A., and Raitt, R.W., 1980, imagine such a slab, which now dips arcward at an angle Crustal structure of the Molucca Sea collision zone, of some 30°, being rotated and uplifted as an eventual Indonesia. In: D.E. Hayes (Editor), The tectonic and result of collision with another forearc. On Simeulue, one geologic evolution of southeast Asian seas and of the forearc islands west of Sumatra, a gravity high islands. Amer. Geop. Union Monog. 23, p. 161-177. similar in size and shape to that on Talaud is associated Milsom, J., Dipowirjo, S., Sain, B., and Sipahutar, J., with a small ophiolite outcrop (Milsom et al., 1990), 1990, Gravity surveys in the north Sumatra forearc. which suggest that rotation, uplift and exposure of United nations CCOP Tech. Bull. 21, p. 85-96. ophiolite slivers can occur in forearc wedges even in the Moore, G.E., and Silver, E.A., 1983, Collision processes absence of collision. Such an origin for the Talaud in the northern Molucca Sea. In: D.E. Hayes Islands and the associated gravity highs seems fully (Editor), The tectonic and geologic evolution of compatible with their structural setting and there is thus southeast Asian seas and islands. Amer. Gcoph. no need to suppose that there has been any collision- Union Monog. 27, p. 360-372. related upthrusting of oceanic crust from the base of the Silver, E.A., and Moore, J.C., 1978, Molucca Sea collision complex. Indeed, such a process might be collision zone, Indonesia: Journ. Geophys. Res., 83, difficult to reconcile with the gravity observations, since p. 1681-1691. it would be expected to result in high values throughout the island group, with peak values in the central region.

It has, nonetheless, to be recognised that surveys throughout the Sumatra forearc (Milsom et al., 1990; Marzuki et a i, 1990) have shown that anomalies such as those observed on Simeulue are the exception rather than the rule, while reflectors displaying the characteristics of oceanic crust have been identified only on one or two lines across the New Britain accretionary wedge. It is thus asking a great deal of coincidence to suppose that

203 Appendix B Gravity Data Reduction Spreadsheet

B.l Example of spreadsheet for gravity data reduction

SORONG FAULT ZONE PROJECT 1993 GRAVITY SURVEYS EAST COAST CENTRAL SULAWESI PRINOPAL FACTS FILE

Drift Rate 3.989E-06 mGal/min Ref.Station Ref.mGal Ref.Gravitv Phi; 3.141592654 G.826 1600 1700 7693.0163 1773.785 978119.94 Rad: 0.017453293 Conversion 1647.24 1750.13 _ Fafion 1.02892 l.02??l

Gravity Tide Tide Drift&Tidc Gbserved G.Normal Bouguer Dcg-to-Rad Coordinates Elev. Time Readings Equivalent Cotr’n Corr’d Corr’d Gravity IGSN 1971 Anomaly Conversion Date Station DLon MLon DLat MLat (m) HH MM Scale.Div mGal mGal mGal mGal mGal mGal mGal

930601 UP-A/P 119 33.00 5 4.00 32.00 10 17 1722.842 1773.632 0.159 1773.791 1773.683 978119.84 978072.07 47.77 0.088430015 930601 PL-A/P 119 53.00 0 52.24 87.00 13 32 1633.209 1681.409 -0.009 1681.400 1681.460 978027.61 978032.99 -5.38 0.015194546 930603 PL-A/P 119 53.00 0 52.24 87.00 6 23 1633.305 1681J08 -0.055 1681.453 1681.549 978027.70 978032.99 -5.29 0.015194546 930603 BB-A/P 122 44.73 1 3.04 • 9 50 1655.296 1704.135 0.144 1704.279 1704.175 978050.33 978033J4 16.79 0.018337011 930603 HM-LUW 122 47.43 0 57.03 2J0 10 40 1645.402 1693.955 0.159 1694.114 1693.994 978040.15 978033.22 6.93 0.016589355 930604 HM-LUW 122 47.43 0 57.03 2J0 19 36 1645.535 1694.092 -0.048 1694.044 1694.123 978040.28 978033.22 7.06 0.016589355 930605 BG-001 123 29.93 1 35J8 IJO 8 12 1738.122 1789.354 -0.022 1789.332 1789J83 978135J 4 978035.77 99.76 0.027744917 930605 HM-LUW 122 47.43 0 57.03 2J0 22 19 1645.580 1694.138 0.076 1694.214 1694.163 978040.32 978033.22 7.10 0.016589355 930606 HM-LUW 122 47.43 0 57.03 2J0 16 18 1645.642 1694.202 0.012 1694.214 1694.223 978040.38 978033.22 7.16 0.016589355 930607 PP-PSO ••••• 13 7 1632.510 1680.690 0.134 1680.824 1680.706 978026.86 978031.80 -4.94 * 930608 PP-PSO ••••• 8 14 1632.676 1680.861 -0.061 1680.800 1680.872 978027.03 978031.80 -4.77 • 930608 PL-KDL 121 20.68 2 0.34 • 22 43 1647.630 1696.247 -0.007 1696.240 1696.255 978042.41 978038.12 4.29 0.035004905 930609 PL-KDL 121 20.68 2 0.34 1.20 8 50 1647.830 1696.453 -0.045 1696.408 1696.459 978042.61 978038.12 4.49 0.035004905 930610 1001 121 20.68 2 0.34 IJO 7 26 1647.782 1696.404 0.005 1696.409 1696.404 978042J6 978038.12 4.44 0.035004905 930610 1002 121 20.88 1 57.97 0.30 7 50 1652.419 1701.175 -0.007 1701.168 1701.175 978047.33 978037.88 9.45 0.034316082 930610 1003 121 19.76 1 55.95 0.75 8 20 1654.652 1703.473 -0.019 1703.454 1703.472 978049.63 978037.67 11.96 0.033727324 930610 1004 121 20.74 1 53.92 0.30 8 51 1659.702 1708.669 -0.027 1708.642 1708.668 978054.82 978037.47 17.36 0.033137694 930610 1005 121 23.24 1 51.89 0.75 9 28 1685.416 1735.126 -0.032 1735.094 1735.126 978081J8 978037.27 44.01 0.032548063 930610 1006 121 20.88 1 56.89 0.30 10 4 1673.253 1722.611 -0.030 1722.581 1722.611 978068.77 978037.77 31.00 0.034002504 930610 1007 121 18.25 1 51.22 0.10 10 37 1663.194 1712.262 -0.023 1712.239 1712.261 978058.42 978037.20 21.21 0.032351423 930610 1008 121 17.84 1 48.38 0.20 11 17 1657.750 1706.660 -0.009 1706.651 1706.659 978052.81 978036.93 15.88 0.031525882 930610 1009 121 20.27 1 46.35 OJO 12 4 1678.075 1727.573 0.012 1727.585 1727J72 978073.73 978036.74 36.99 0.030936252 930610 1010 121 22JO 1 48 J1 0.60 13 28 1681.006 1730J89 0.055 1730.644 1730.587 978076.74 978036.94 39.80 0.031565443 930610 1011 121 25.00 1 49.19 0.30 14 2 1672.640 1721.981 0.070 1722.051 1721.979 978068.13 978037.01 31.13 0.031761793 930610 1012 121 26.76 1 50.27 0.30 14 38 1675.446 1724.868 0.082 1724.950 1724.866 978071.02 978037.11 33.91 0.032076243 930610 1013 121 31.35 1 53.92 -0.50 16 20 1665.610 1714.747 0.090 1714.837 1714.745 978060.90 978037.47 23.43 0.033137694 930610 1014 121 34.49 1 57.16 OJO 17 12 1650.530 1699.231 0.079 1699J10 1699.229 978045.38 978037.79 7 J9 0.034081044 930611 2014 121 34.49 1 57.20 OJO 5 38 1650J00 1699.200 0.084 1699.284 1699.195 978045.35 978037.80 7J5 0.034092098 930611 2015 121 30.47 1 56.90 OJO 6 41 1658.465 1707.396 0.059 1707.455 1707.390 978053J5 978037.77 15.78 0.034004832 930611 2016 121 32.19 2 2.97 0.60 7 51 1641.480 1689.920 0.026 1689.946 1689.914 978036.07 978038.40 -2.33 0.035771396 930611 2017 121 32.19 2 2.97 0.75 7 58 1641J40 1689.981 0.022 1690.003 1689.975 978036.13 978038.40 -2.27 0.035771687 930611 2018 121 3236 2 6.22 0.75 9 6 1650.480 1699.180 -0.005 1699.175 1699.174 978045J3 978038.76 6 J7 0.036714746 930611 2019 121 30.27 2 2J7 -OJO 10 14 1645.694 1694.255 -0.019 1694.236 1694.249 978040.40 978038J6 2.04 0.035653586 930611 2020 121 25.68 1 57J7 0.75 11 32 1654.962 1703.792 -0.014 1703.778 1703.785 978049.94 978037.84 12.10 0.034199145 930611 2021 121 27 JO 1 59.87 OJO 13 30 1650.624 1699J28 0.028 1699.356 1699J21 978045.48 978038.07 7.40 0.034867315 930611 2022 121 28.44 1 55J4 0.75 14 42 1660.463 1709.452 0.058 1709.510 1709.444 978055.60 978037.63 17.97 0.033609515 930611 2023 121 26.62 1 54.87 OJO 15 13 1663.960 1713.050 0.068 1713.118 1713.042 978059.20 978037.56 21.64 0.033412874 930611 2024 121 23.72 1 54.46 OJO 15 50 1661J10 1710.529 0.078 1710.607 1710.521 978056.68 978037.52 19.15 0.033295064 930611 2025 121 22JO 1 56.08 OJO 16 41 1655.712 1704.563 0.084 1704.647 1704.555 978050.71 978037.68 13.03 0.033766594 930611 2026 121 22JO 1 58.72 OJO 17 16 1649.546 1698.219 0.083 1698 J02 1698.211 978044.37 978037.95 6.41 0.034533085 930611 2001 121 20.68 2 0.34 1.20 17 45 1647.723 1696.343 0.079 1696.422 1696.335 978042.49 978038.12 4.37 0.035005487 930613 3001 121 20.68 2 0.34 1.20 7 17 1647.693 1696.312 0.870 1697.182 1696.295 978042.45 978038.12 4.33 0.035005487 930613 3027 121 32.97 2 9.79 0.75 10 14 1644.040 1692.554 0.027 1692.581 1692.536 978038.69 978039.16 -0.47 0.037755253 930613 3028 121 36.15 2 12J2 OJO 12 10 1653.000 1701.773 -0.009 1701.764 1701.754 978047.91 978039.47 8.44 0.038548505 930613 3029 121 44.93 2 12.77 0.60 13 33 1649.237 1697.901 -0.011 1697.890 1697.882 978044.04 978039.50 4.54 0.038620646 930613 3030 121 45.81 2 15.54 OJO 14 1 1649.410 1698.079 -0.006 1698.073 1698.060 978044.22 978039.82 4.39 0.039426988 930613 3031 121 48.44 2 17.84 OJO 14 35 1644.950 1693.490 0.003 1693.493 1693.471 978039.63 978040.10 -0.47 0.040094576 930613 3032 121 50.47 2 21.28 OJO 16 8 1644.400 1692.924 0.036 1692.960 1692.905 978039.06 978040.52 -1.46 0.041097559 930613 WGSU 121 50.05 2 21.55 5.00 20 1 1644.565 1693.094 0.079 1693.173 1693.074 978039.23 978040.55 -1J2 0.041176099 930614 WGSU 121 50.05 2 21.55 5.00 7 27 1644.583 1693.112 0.096 1693.208 1693.089 978039.24 978040.55 -1.30 0.041176099 930614 4033 121 52.97 2 25.14 OJO 8 37 1653.182 1701.960 0.090 1702.050 1701.937 978048.09 978041.00 7.10 0.042218060 930614 4034 121 55J4 2 28.54 OJO 9 34 1660.930 1709.932 0.072 1710.004 1709.909 978056.06 978041.43 14.63 0.043209116 930614 4035 121 57.97 2 32.65 0.30 10 17 1670.142 1719.411 0.053 1719.464 1719.387 978065.54 978041.97 23.57 0.044404667 930614 4036 121 59.73 2 36.79 OJO 12 39 1680.160 1729.718 -0.011 1729.707 1729.694 978075.85 978042.53 33J2 0.045608071 930614 4037 122 0.57 2 40.41 0.75 13 30 1677.253 1726.727 -0.021 1726.706 1726.703 978072.86 978043.03 29.83 0.046659923 930614 4038 122 3.78 2 45.61 OJO 14 55 1683.190 1732.836 -0.017 1732.819 1732.811 978078.97 978043.77 35.19 0.048173414 930614 4039 122 8.07 2 47.33 -0.50 15 46 1676.400 1725.849 -0.001 1725.848 1725.825 978071.98 9/8044.02 27.96 0.048674033 930614 LAILIA 122 9.32 2 48.44 5.00 17 31 1687.542 1737.314 0.045 1737.359 1737.288 978083.44 978044.19 39.26 0.048998083 930615 LAILIA 122 9.32 2 48.44 5.00 6 43 1687.580 1737J53 0.078 1737.431 1737.324 978083.48 978044.19 39.29 0.048998083 930615 5040 122 10.80 2 51.75 1.00 7 43 1702.343 1752.541 0.102 1752.643 1752.512 978098.67 978044.68 53.99 0.049960050 930615 5041 122 11.61 2 52.70 2.00 8 9 1703.560 1753.793 0.107 1753.900 1753.764 978099.92 978044.82 55.10 0.050234939 930615 5042 122 11.14 2 49.73 OJO 8 48 1698.185 1748.265 0.108 1748J73 1748.235 978094J9 978044.37 50.02 0.049371001 930615 5039 122 8.07 2 47.33 1J0 9 30 1676.150 1725.592 0.101 1725.693 1725.563 978071.72 978044.02 27.70 0.048674033 930615 5043 122 5.20 2 47.16 OJO 10 11 1684.090 1733.762 0.086 1733.848 1733.733 978079.89 978044.00 35.89 0.048624873 930615 5044 122 1.08 2 43.38 0.75 11 7 1663.680 1712.762 0.057 1712.819 1712.732 978058.89 978043.45 15.44 0.047523861 930615 BUNGKU 121 58.04 2 32.97 3.00 16 52 1669.970 1719.234 -0.006 1719.228 1719.203 978065.36 978042.02 23J4 0.044497169 930616 BUNGKU 121 58.04 2 32.97 3.00 6 6 1669.920 1719.182 0.028 1719.210 1719.148 978065.30 978042.02 23.29 0.044497169 930616 6045 121 52.09 2 24.06 0.25 8 44 1646.310 1694.889 0.116 1695.005 1694.855 978041.01 978040.86 0.15 0.041903901 930616 6046 121 40.74 2 10.41 0.75 15 13 1655.060 1703.892 -0.054 1703.838 1703.856 978050.01 978039.23 10.79 0.037933277 930616 6047 121 38J8 2 11.25 -0.50 15 50 1651.932 1700.674 -0.054 1700.620 1700.637 978046.79 978039.32 7.47 0.038178787 930616 UNGKAYA 121 35.41 2 12.90 • 17 2 1640.460 1688.870 -0.034 1688.836 1688.833 978034.99 978039.51 -4.52 0.038659916 930617 UNGKAYA 121 35.41 2 12.90 • 6 33 1640.398 1688.806 -0.013 1688.793 1688.766 978034.92 978039.51 -4.59 0.038659916 930617 7001 121 20.68 2 0.34 1.20 9 25 1647.437 1696.049 0.127 1696.176 1696.008 978042.16 978038.12 4.04 0.035005487 930619 RATA 122 5.60 1 36.95 0.10 13 5 1677.050 1726.518 0.103 1726.621 1726.465 978072.62 978035.91 36.71 0.028202484 930619 HM-LUW 122 47.43 0 57.03 2J0 17 44 1645.686 1694.247 -0.092 1694.155 1694.193 978040.35 978033.22 7.13 0.016589355 930620 BB-A/P 122 44.73 1 3.04 • 6 22 1655.520 1704.366 -0.090 1704.276 1704J08 978050.46 978033.54 16.93 0.018337011 930621 PL-/V/P 119 53.00 0 52.24 87.00 13 35 1633.160 1681.359 0.150 1681.509 1681.294 978027.45 978032.99 -5.54 0.015194546 930621 UP-A/P 119 33.00 5 4.00 32.00 16 3 1722.955 1773.749 0.028 1773.777 1773.683 978119.84 978072.07 47.77 0.088430015

204 B.2. Spreadsheet templates for gravity data reduction

Al: [W7] N14: (G) [W ll] '"Con’d A2: [W7] 014: (G) [WIO] 'Gravity A4: (G) [W7] ’SORONG FAULT ZONE PROJECT 1993 P14: (G) [W ll] '"IGSN 1971 K4: (G) [W9] ^ Q14: (G) [W7] '"Anomaly A5: (G) [W7] ’GRAVITY SURVEYS EAST COAST A15: (G) [W7] '"Date CENTRAL SULAWESI B15: (G) [WIO] '"Number K5: (G) [W9] ^ C15: (G) [W5] ’DLon A6: (G) [W7] ’PRINCIPAL FACTS FILE D15: (G) [W6] ’MLon Q6: (G) [W7] ’ E15: (G) [W5] ’DLat R6: (G) [WIO] Xüonv.Const: F15: (G) [W6] ’MLat A8: (G) [W7] ’ G15: (G) [W6] ’(m) J8: (G) [W ll]’Drift Rate: H15: (G) [W3] ’HH K8: (G) [W9] 115: (G) [W4] ’MM (K93-K16)/((A93-A16)*24*60+(H93-H16)*60+(I93-I16)) J15: (G) [W ll] '"Readings L8: (G) [W8] ’mGal/min K15: (G) [W9] '"mGal N8: (G) [W ll] '^Ref.Station L15: (G) [W8] '"mGal 08: (G) [WIO] ^RefmGal M15: (G) [W9] '"mGal P8: (G) [W ll] ^Ref.Gravity N15:(G) [Wll]'"mGal Q8: (G) [W7] ^Phi: 015: (G) [WIO] '"mGal R8: (F6) [WIO] 3.141592654 P15: (G) [Wll]'"mGal A9: (G) [W7] ’ Q15: (G) [W7] ^ G a l J9: (G) [W ll]’G.826 A16: (G) [W7] 930601 K9: (G) [W9] 1600 B16: (G) [WIO] ‘UP-A/P L9: (G) [W8] 1700 C16: (G) [W5] 119 N9: (G) [W ll] 7693.0163 D16: (F2) [W6] 33 09: (G) [WIO] 1773.785 E16: (G) [W5] 5 P9: (G) [W ll] 978119.94 F16: (F2) [W6] 4 Q9: (G) [W7] ^Rad: G16: (FI) [W6] 32 R9: (F6) [WIO] (2*$R$8)/360 H16: (G) [W3] 10 AlO: (G) [W7] ’ 116: (G) [W4] 17 JIO: (G) [W ll] ’Conversion J16: (F2) [W ll] 1722.842 KIO: (G) [W9] 1647.24 K16: (F2) [W9] LIO: (G) [W8] 1750.13 ((J16-1700)*1.02891+1750.13) J11:(G) [W ll]’Factors : L16: (F2) [W8] 0.159 K ll: (G) [W9] 1.02892 M16: (F2) [W9] +K16+L16 L11:(G)[W8] 1.02891 N16: (F2) [W ll] Q11:(G)[W7]’ (K16-((A16-$A$29)*24*60+(H16-$H$29)* Q12: (G) [W7] ^Simple 60+ai6-$I$29))*$K$8) L13: (G) [W8] ^Tide 016: (F2) [WIO] +$P$9+(N16-$0$9) M13: (G) [W9] '"Tide P16: (F2)[W11] N13: (G) [W ll] ^Drift&Tide 978031.85*(1+0.0053024*(@SIN(R16)*@ 013: (G) [WIO] 'XDbserved SIN(R16))-0.0000059*(@SIN(2*R16)*@SI P13: (G) [W ll] ^.Normal N(2*R16))) Q13: (G) [W7] '^Bouguer Q16: (F2) [W7] +016-P16 B14: (G) [WIO] '"Station R16: (F6) [WIO] (E16+(F16/60))*$R$9 C14: (G) [W5] ’Coordinates A17: (G) [W7] 930601 G14: (G) [W6] ’Elev. B17: (G) [WIO] ’’PL-A/P H14: (G) [W3] ’Time C17: (G) [W5] 119 J14: (G) [W ll] '"Scale.Div D17: (F2) [W6] 53 K14: (G) [W9] '"Equiv. E17: (G) [W5] 0 L14: (G) [W8] 'XZorr’n F17: (F2) [W6] 52.235 M14: (G) [W9] '"Corr’d G17: (FI) [W6] 87 205 H17: (G) [W3] 13 Q19: (F2) [W7] +019-P19 117: (G) [W4] 32 R19: (F6) [WIO] (E19+(F19/60))*$R$9 J17: (F2) [W ll] 1633.209 A20: (G) [W7] 930603 K17: (F2) [W9] ((J17-1600)* 1.02892+1647.24) B20: (G) [WIO] "HM-LUW L17: (F2) [W8] -0.009 C20: (G) [W5] 122 M17: (F2) [W9] +K17+L17 D20: (F2) [W6] 47.43 N17: (F2) [W ll] E20: (G) [W5] 0 (K17-((A17-$A$29)*24*60+(H17-$H$29)*60+(I17-$I$29))*$ F20: (F2) [W6] 57.03 K$8) G20: (Fl) [W6] 2.5 017: (F2) [WIO] +$P$9+(N17-$0$9) H20: (G) [W3] 10 P17: (F2) [W ll] 120: (G) [W4] 40 978031.85*(l+0.0053024*(@SIN(R17)*@SIN(R17))-0.00000 J20: (F2) [W ll] 1645.402 59*(@SIN(2*R17)*@SIN(2*R17))) K20: (F2) [W9] Q17: (F2) [W7] +017-P17 ((J20-1600)*1.02892+1647.24) R17: (F6) [WIO] (E17+(F17/60))*$R$9 L20: (F2) [W8] 0.159 A18: (G) [W7] 930603 M20: (F2) [W9] +K20+L20 B18: (G) [WIO] "PL-A/P N20: (F2) [W ll] C18: (G) [W5] 119 (K20-((A20-$A$29)*24*60+(H20-$H$29)* D18: (F2) [W6] 53 60+(I20-$I$29))*$K$8) E18: (G) [W5] 0 020: (F2) [WIO] +$P$9+(N20-$O$9) F18: (F2) [W6] 52.235 P20: (F2) [W ll] G18: (Fl) [W6] 87 978031.85*(1+0.0053024*(@SIN(R20)*@ H18: (G) [W3] 6 SIN(R20))-0.0000059*(@SIN(2*R20)*@SI 118: (G) [W4] 23 N(2*R20))) J18:(F2) [W ll] 1633.305 Q20: (F2) [W7] +020-P20 K18: (F2) [W9] ((J18-1600)*1.02892+1647.24) R20: (F6) [WIO] (E20+(F20/60))*$R$9 L18: (F2) [W8] -0.055 A21: (G) [W7] 930604 M18: (F2) [W9] +K18+L18 B21: (G) [WIO] "HM-LUW N18: (F2)[W11] C21: (G) [W5] 122 (K18-((A18-$A$29)*24*60+(H18-$H$29)*60+ai8-$I$29))*$ D21: (F2) [W6] 47.43 K$8) E21: (G) [W5] 0 018: (F2) [WIO] +$P$9+(N18-$0$9) F21: (F2) [W6] 57.03 P18: (F2) [W ll] G21: (Fl) [W6] 2.5 978031.85*(l+0.0053024*(@SIN(R18)*@SIN(R18))-0.00000 H21: (G) [W3] 19 59*(@SIN(2*R18)*@SIN(2*R18))) 121: (G) [W4] 36 Q18: (F2)[W7] +018-P18 J21:(F2) [W ll] 1645.535 R18: (F6) [WIO] (E18+(F18/60))*$R$9 K21: (F2) [W9] A19: (G) [W7] 930603 ((J21-1600)*1.02892+1647.24) B19: (G) [WIO] "BB-A/P L21: (F2) [W8] -0.048 C19: (G) [W5] 122 M21: (F2) [W9] +K21+L21 D19: (F2) [W6] 44.73 N21:(F2) [Wll] E19: (G) [W5] 1 (K21-((A21-$A$29)*24*60+(H21-$H$29)* F19: (F2) [W6] 3.038 60+(I21-$I$29))*$K$8) G19: (Fl) [W6] '* 021: (F2) [WIO] +$P$9+(N21-$0$9) H19: (G) [W3] 9 P21:(F2)[W11] 119: (G) [W4] 50 978031.85*(1+0.0053024*(@SIN(R21)*@ J19: (F2) [W ll] 1655.296 SIN(R21))-0.0000059*(@SIN(2*R21)*@SI K19: (F2) [W9] ((J19-1600)* 1.02892+1647.24) N(2*R21))) L19: (F2) [W8] 0.144 Q21: (F2) [W7] +021-P21 M19: (F2) [W9] +K19+L19 R21: (F6) [WIO] (E21+(F21/60))*$R$9 N19: (F2) [W ll] A22: (G) [W7] 930605 (K19-((A19-$A$29)*24*60+(H19-$H$29)*60+(I19-$I$29))*$ B22: (G) [WIO] "BG-001 K$8) C22: (G) [W5] 123 019: (F2) [WIO] +$P$9+(N19-$0$9) D22: (F2) [W6] 29.93 P19: (F2) [W ll] E22: (G) [W5] 1 978031.85*(l+0.0053024*(@SIN(R19)*@SIN(R19))-0.00000 F22: (F2) [W6] 35.38 59*(@SIN(2*R19)*@SIN(2*R19))) G22: (Fl) [W6] 1.5 206 H22: (G) [W3] 8 Q24: (F2) [W7] +024-P24 122: (G) [W4] 12 R24: (F6) [WIO] (E24+(F24/60))*$R$9 J22: (F2) [W ll] 1738.122 A25: (G) [W7] 930607 K22: (F2) [W9] ((J22-1700)*1.02891+1750.13) B25: (G) [WIO] "PP-PSO L22: (F2) [W8] -0.022 C25: (G) [W5] '* M22: (F2) [W9] +K22+L22 D25: (F2) [W6] '* N22: (F2) [W ll] E25: (G) [W5] '* (K22-((A22-$A$29)*24*60+(H22-$H$29)*60+(I22-$I$29))*$ F25: (F2) [W6] '* K$8) G25: (Fl) [W6] ’* 022: (F2) [WIO] +$P$9+(N22-$0$9) H25: (G) [W3] 13 P22: (F2) [W ll] 125: (G) [W4] 7 978031.85*(l+0.0053024*(@SIN(R22)*@SIN(R22))-0.00000 J25: (F2) [W ll] 1632.51 59*(@SIN(2*R22)*@SIN(2*R22))) K25: (F2) [W9] Q22: (F2) [W7] +022-P22 ((J25-1600)*1.02892+1647.24) R22: (F6) [WIO] (E22+(F22/60))*$R$9 L25: (F2) [W8] 0.134 A23: (G) [W7] 930605 M25: (F2) [W9] +K25+L25 B23: (G) [WIO] "HM-LUW N25: (F2) [W ll] C23: (G) [W5] 122 (K25-((A25-$A$29)*24*60+(H25-$H$29)* D23: (F2) [W6] 47.43 60+(I25-$I$29))*$K$8) E23: (G) [W5] 0 025: (F2) [WIO] +$P$9+(N25-$0$9) F23: (F2) [W6] 57.03 P25: (F2) [W ll] G23: (Fl) [W6] 2.5 978031.85*(1+0.0053024*(@SIN(R25)*@ H23: (G) [W3] 22 SIN(R25))-0.0000059*(@SIN(2*R25)*@SI 123: (G) [W4] 19 N(2*R25))) J23:(F2) [W ll] 1645.58 Q25: (F2) [W7] +025-P25 K23: (F2) [W9] ((J23-1600)* 1.02892+1647.24) R25: (F6) [WIO] (E25+(F25/60))*$R$9 L23: (F2) [W8] 0.076 A26: (G) [W7] 930608 M23: (F2) [W9] +K23+L23 B26: (G) [WIO] "PP-PSO N23:(F2) [Wll] C26: (G) [W5] '* (K23-((A23-$A$29)*24*60+(H23-$H$29)*60+(I23-$I$29))*$ D26: (F2) [W6] '* K$8) E26: (G) [W5] '* 023: (F2) [WIO] +$P$9+(N23-$0$9) F26: (F2) [W6] ’* P23:(F2) [Wll] G26: (Fl) [W6] '* 978031.85*(l+0.0053024*(@SIN(R23)*@SIN(R23))-0.00000 H26: (G) [W3] 8 59*(@SIN(2*R23)*@SIN(2*R23))) 126: (G) [W4] 14 Q23: (F2) [W7] +023-P23 J26: (F2) [W ll] 1632.676 R23: (F6) [WIO] (E23+(F23/60))*$R$9 K26: (F2) [W9] A24: (G) [W7] 930606 ((J26-1600)*1.02892+1647.24) B24: (G) [WIO] "HM-LUW L26: (F2) [W8] -0.061 C24: (G) [W5] 122 M26: (F2) [W9] +K26+L26 D24: (F2) [W6] 47.43 N26: (F2) [W ll] E24: (G) [W5] 0 (K26-((A26-$A$29)*24*60+(H26-$H$29)* F24: (F2) [W6] 57.03 60+(I26-$I$29))*$K$8) G24: (Fl) [W6] 2.5 026: (F2) [WIO] +$P$9+(N26-$0$9) H24: (G) [W3] 16 P26: (F2) [W ll] 124: (G) [W4] 18 978031.85*(1+0.0053024*(@SIN(R26)*@ J24: (F2)[W11] 1645.642 SIN(R26))-0.0000059*(@SIN(2*R26)*@SI K24: (F2) [W9] ((J24-1600)* 1.02892+1647.24) N(2*R26))) L24: (F2) [W8] 0.012 Q26: (F2) [W7] +026-P26 M24: (F2) [W9] +K24+L24 R26: (F6) [WIO] (E26+(F26/60))*$R$9 N24: (F2) [W ll] A27: (G) [W7] 930608 (K24-((A24-$A$29)*24*60+(H24-$H$29)*60+(I24-$I$29))*$ B27: (G) [WIO] "PL-KDL K$8) C27: (G) [W5] 121 024: (F2) [WIO] +$P$9+(N24-$0$9) D27: (F2) [W6] 20.675 P24: (F2) [W ll] E27: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R24)*@SIN(R24))-0.00000 F27: (F2) [W6] 0.338 59*(@SIN(2*R24)*@SIN(2*R24))) G27: (Fl) [W6] '* 207 H27: (G) [W3] 22 Q29: (F2) [W7] +029-P29 127: (G) [W4] 43 R29: (F6) [WIO] (E29+(F29/60))*$R$9 J27: (F2) [W ll] 1647.63 A30: (G) [W7] 930610 K27: (F2) [W9] ((J27-1600)* 1.02892+1647.24) B30: (G) [WIO] +B29+1 L27: (F2) [W8] -0.007 C30: (G) [W5] 121 M27: (F2) [W9] +K27+L27 D30: (F2) [W6] 20.878 N27: (F2) [W ll] E30: (G) [W5] 1 (K27-((A27-$A$29)*24*60+(H27-$H$29)*60+(I27-$I$29))*$ F30: (F2) [W6] 57.97 K$8) G30: (Fl) [W6] 0.3 027: (F2) [WIO] +$P$9+(N27-$0$9) H30: (G) [W3] 7 P27: (F2) [W ll] 130: (G) [W4] 50 978031.85*(l+0.0053024*(@SIN(R27)*@SIN(R27))-0.00000 J30: (F2) [W ll] 1652.419 59*(@SIN(2*R27)*@SIN(2*R27))) K30: (F2) [W9] Q27: (F2) [W7] +027-P27 ((J30-1600)*1.02892+1647.24) R27: (F6) [WIO] (E27+(F27/60))*$R$9 L30: (F2) [W8] -0.007 A28: (G) [W7] 930609 M30: (F2) [W9] +K30+L30 B28: (G) [WIO] "PL-KDL N30: (F2) [W ll] C28: (G) [W5] 121 (K30-((A30-$A$29)*24*60+(H30-$H$29)* D28: (F2) [W6] 20.675 60+(I30-$I$29))*$K$8) E28: (G) [W5] 2 030: (F2) [WIO] +$P$9+(N30-$O$9) F28: (F2) [W6] 0.338 P30: (F2)[W11] G28: (Fl) [W6] 1.2 978031.85*(1+0.0053024*(@SIN(R30)*@ H28: (G) [W3] 8 SIN(R30))-0.0000059*(@SIN(2*R30)*@SI 128: (G) [W4] 50 N(2*R30))) J28: (F2) [W ll] 1647.83 Q30: (F2) [W7] +030-P30 K28: (F2) [W9] ((J28-1600)* 1.02892+1647.24) R30: (F6) [WIO] (E30+(F30/60))*$R$9 L28: (F2) [W8] -0.045 A31: (G) [W7] 930610 M28: (F2) [W9] +K28+L28 B31:(G)[W10]+B30+1 N28: (F2) [W ll] C31: (G) [W5] 121 (K28-((A28-$A$29)*24*60+(H28-$H$29)*60+(I28-$I$29))*$ D31: (F2) [W6] 19.757 K$8) E31: (G) [W5] 1 028: (F2) [WIO] +$P$9+(N28-$0$9) F31: (F2) [W6] 55.946 P28: (F2) [W ll] G31:(F1)[W6] 0.75 978031.85*(l+0.0053024*(@SIN(R28)*@SIN(R28))-0.00000 H31:(G)[W3]8 59*(@SIN(2*R28)*@SIN(2*R28))) 131: (G) [W4] 20 Q28: (F2) [W7] +028-P28 J31:(F2) [W ll] 1654.652 R28: (F6) [WIO] (E28+(F28/60))*$R$9 K31: (F2) [W9] A29: (G) [W7] 930610 ((J31-1600)*1.02892+1647.24) B29: (G) [WIO] 1001 L31: (F2) [W8] -0.019 C29: (G) [W5] 121 M31:(F2)[W9]+K31+L31 D29: (F2) [W6] 20.675 N31:(F2) [Wll] E29: (G) [W5] 2 (K31-((A31-$A$29)*24*60+(H31-$H$29)* F29: (F2) [W6] 0.338 60+(I31-$I$29))*$K$8) G29: (Fl) [W6] 1.2 031: (F2) [WIO] +$P$9+(N31-$0$9) H29: (G) [W3] 7 P31:(F2)[W11] 129: (G) [W4] 26 978031.85*(1+0.0053024*(@SIN(R31)*@ J29: (F2)[W11] 1647.782 SIN(R31))-0.0000059*(@SIN(2*R31)*@SI K29: (F2) [W9] ((J29-1600)*1.02892+1647.24) N(2*R31))) L29: (F2) [W8] 0.005 Q31:(F2)[W7] +031-P31 M29: (F2) [W9] +K29+L29 R31: (F6) [WIO] (E31+(F31/60))*$R$9 N29: (F2) [W ll] A32: (G) [W7] 930610 (K29-((A29-$A$29)*24*60+(H29-$H$29)*60+(I29-$I$29))*$ B32:(G)[W10]+B31+1 K$8) C32: (G) [W5] 121 029: (F2) [WIO] +$P$9+(N29-$0$9) D32: (F2) [W6] 20.743 P29: (F2) [W ll] E32: (G) [W5] 1 978031.85*(l+0.0053024*(@SIN(R29)*@SIN(R29))-0.00000 F32: (F2) [W6] 53.919 59*(@SIN(2*R29)*@SIN(2*R29))) G32: (Fl) [W6] 0.3 208 H32: (G) [W3] 8 Q34: (F2) [W7] +034-P34 132: (G) [W4] 51 R34: (F6) [WIO] (E34+(F34/60))*$R$9 J32: (F2) [W ll] 1659.702 A35: (G) [W7] 930610 K32: (F2) [W9] ((J32-1600)* 1.02892+1647.24) B35: (G) [WIO] +B34+1 L32: (F2) [W8] -0.027 C35: (G) [W5] 121 M32: (F2) [W9] +K32+L32 D35: (F2) [W6] 18.245 N32: (F2)[W11] E35: (G) [W5] 1 (K32-((A32-$A$29)*24*60+(H32-$H$29)*60+(I32-$I$29))*$ F35: (F2) [W6] 51.216 K$8) G35: (Fl) [W6] 0.1 032: (F2) [WIO] +$P$9+(N32-$0$9) H35: (G) [W3] 10 P32: (F2) [W ll] 135: (G) [W4] 37 978031.85*(l+0.0053024*(@SIN(R32)*@SIN(R32))-0.00000 J35: (F2) [W ll] 1663.194 59*(@SIN(2*R32)*@SIN(2*R32))) K35: (F2) [W9] Q32: (F2) [W7] +032-P32 ((J35-1600)*1.02892+1647.24) R32: (F6) [WIO] (E32+(F32/60))*$R$9 L35: (F2) [W8] -0.023 A33: (G) [W7] 930610 M35: (F2) [W9] +K35+L35 B33: (G) [WIO] +B32+1 N35:(F2)[W11] C33: (G) [W5] 121 (K35-((A35-$A$29)*24*60+(H35-$H$29)* D33: (F2) [W6] 23.24 60+(I35-$I$29))*$K$8) E33: (G) [W5] 1 035: (F2) [WIO] +$P$9+(N35-$0$9) F33: (F2) [W6] 51.892 P35: (F2)[W11] G33: (Fl) [W6] 0.75 978031.85*(1+0.0053024*(@SIN(R35)*@ H33: (G) [W3] 9 SIN(R35))-0.0000059*(@SIN(2*R35)*@SI 133: (G) [W4] 28 N(2*R35))) J33:(F2)[W11] 1685.416 Q35: (F2) [W7] +035-P35 K33: (F2) [W9] ((J33-1600)* 1.02892+1647.24) R35: (F6) [WIO] (E35+(F35/60))*$R$9 L33: (F2) [W8] -0.032 A36: (G) [W7] 930610 M33: (F2) [W9] +K33+L33 B36: (G) [WIO] +B35+1 N33:(F2) [Wll] C36: (G) [W5] 121 (K33-((A33-$A$29)*24*60+(H33-$H$29)*60+(I33-$I$29))*$ D36: (F2) [W6] 17.84 K$8) E36: (G) [W5] 1 033: (F2) [WIO] +$P$9+(N33-$0$9) F36: (F2) [W6] 48.378 P33:(F2) [W ll] G36: (Fl) [W6] 0.2 978031.85*(l+0.0053024*(@SIN(R33)*@SIN(R33))-0.00000 H36: (G) [W3] 11 59*(@SIN(2*R33)*@SIN(2*R33))) 136: (G) [W4] 17 Q33: (F2) [W7] +033-P33 J36: (F2) [W ll] 1657.75 R33: (F6) [WIO] (E33+(F33/60))*$R$9 K36: (F2) [W9] A34: (G) [W7] 930610 ((J36-1600)*1.02892+1647.24) B34: (G) [WIO] +B33+1 L36: (F2) [W8] -0.009 C34: (G) [W5] 121 M36: (F2) [W9] +K36+L36 D34: (F2) [W6] 20.878 N36: (F2) [W ll] E34: (G) [W5] 1 (K36-((A36-$A$29)*24*60+(H36-$H$29)* F34: (F2) [W6] 56.892 60+(I36-$I$29))*$K$8) G34: (Fl) [W6] 0.3 036: (F2) [WIO] +$P$9+(N36-$0$9) H34: (G) [W3] 10 P36: (F2)[W11] 134: (G) [W4] 4 978031.85*(1+0.0053024*(@SIN(R36)*@ J34: (F2) [W ll] 1673.253 SIN(R36))-0.0000059*(@SIN(2*R36)*@SI K34: (F2) [W9] ((J34-1600)* 1.02892+1647.24) N(2*R36))) L34: (F2) [W8] -0.03 Q36: (F2) [W7] +036-P36 M34: (F2) [W9] +K34+L34 R36: (F6) [WIO] (E36+(F36/60))*$R$9 N34: (F2) [W ll] A37: (G) [W7] 930610 (K34-((A34-$A$29)*24*60+(H34-$H$29)*60+(I34-$I$29))*$ B37: (G) [WIO] +B36+1 K$8) C37: (G) [W5] 121 034: (F2) [WIO] +$P$9+(N34-$0$9) D37: (F2) [W6] 20.27 P34: (F2)[W11] E37: (G) [W5] 1 978031.85*(l+0.0053024*(@SIN(R34)*@SIN(R34))-0.00000 F37: (F2) [W6] 46.351 59*(@SIN(2*R34)*@SIN(2*R34))) G37: (Fl) [W6] 0.5 209 H37: (G) [W3] 12 Q39: (F2) [W7] +039-P39 137: (G) [W4] 4 R39: (F6) [WIO] (E39+(F39/60))*$R$9 J37: (F2) [W ll] 1678.075 A40: (G) [W7] 930610 K37: (F2) [W9] ((J37-1600)*1.02892+1647.24) B40: (G) [WIO] +B39+1 L37: (F2) [W8] 0.012 C40: (G) [W5] 121 M37: (F2) [W9] +K37+L37 D40: (F2) [W6] 26.755 N37: (F2) [W ll] E40: (G) [W5] 1 (K37-((A37-$A$29)*24*60+(H37-$H$29)*60+(I37-$I$29))*$ F40: (F2) [W6] 50.27 K$8) G40: (Fl) [W6] 0.3 037: (F2) [WIO] +$P$9+(N37-$0$9) H40: (G) [W3] 14 P37: (F2) [W ll] 140: (G) [W4] 38 978031.85*(l+0.0053024*(@SIN(R37)*@SIN(R37))-0.00000 J40: (F2) [W ll] 1675.446 59*(@SIN(2*R37)*@SIN(2*R37))) K40: (F2) [W9] Q37: (F2) [W7] +037-P37 ((J40-1600)*1.02892+1647.24) R37: (F6) [WIO] (E37+(F37/60))*$R$9 L40: (F2) [W8] 0.082 A38: (G) [W7] 930610 M40: (F2) [W9] +K40+L40 B38: (G) [WIO] +B37+1 N40: (F2) [W ll] C38: (G) [W5] 121 (K40-((A40-$A$29)*24*60+(H40-$H$29)* D38: (F2) [W6] 22.295 60+(I40-$I$29))*$K$8) E38: (G) [W5] 1 040: (F2) [WIO] +$P$9+(N40-$O$9) F38: (F2) [W6] 48.514 P40: (F2) [W ll] G38: (Fl) [W6] 0.6 978031.85*(1+0.0053024*(@SIN(R40)*@ H38: (G) [W3] 13 SIN(R40))-0.0000059*(@SIN(2*R40)*@SI 138: (G) [W4] 28 N(2*R40))) J38: (F2) [W ll] 1681.006 Q40: (F2) [W7] +040-P40 K38: (F2) [W9] ((J38-1600)* 1.02892+1647.24) R40: (F6) [WIO] (E40+(F40/60))*$R$9 L38: (F2) [W8] 0.055 A41: (G) [W7] 930610 M38: (F2) [W9] +K38+L38 B41: (G) [WIO]+B40+1 N38: (F2) [W ll] C41: (G) [W5] 121 (K38-((A38-$A$29)*24*60+(H38-$H$29)*60+(I38-$I$29))*$ D41:(F2) [W6] 31.35 K$8) E41: (G) [W5] 1 038: (F2) [WIO] +$P$9+(N38-$0$9) F41: (F2) [W6] 53.919 P38:(F2) [Wll] G41:(F1)[W6] -0.5 978031.85*(l+0.0053024*(@SIN(R38)*@SIN(R38))-0.00000 H41: (G) [W3] 16 59*(@SIN(2*R38)*@SIN(2*R38))) 141: (G) [W4] 20 Q38: (F2) [W7] +038-P38 J41:(F2) [W ll] 1665.61 R38: (F6) [WIO] (E38+(F38/60))*$R$9 K41: (F2) [W9] A39: (G) [W7] 930610 ((J41-1600)*1.02892+1647.24) B39: (G) [WIO] +B38+1 L41: (F2) [W8] 0.09 C39: (G) [W5] 121 M41: (F2) [W9] +K41+L41 D39: (F2) [W6] 24.995 N41:(F2)[W11] E39: (G) [W5] 1 (K41-((A41-$A$29)*24*60+(H41-$H$29)* F39: (F2) [W6] 49.189 60+(I41-$I$29))*$K$8) G39: (Fl) [W6] 0.3 041: (F2) [WIO] +$P$9+(N41-$0$9) H39: (G) [W3] 14 P41: (F2) [W ll] 139: (G) [W4] 2 978031.85*(1+0.0053024*(@SIN(R41)*@ J39: (F2)[W11] 1672.64 SIN(R41))-0.0000059*(@SIN(2*R41)*@SI K39: (F2) [W9] ((J39-1600)* 1.02892+1647.24) N(2*R41))) L39: (F2) [W8] 0.07 Q41: (F2) [W7] +041-P41 M39: (F2) [W9] +K39+L39 R41: (F6) [WIO] (E41+(F41/60))*$R$9 N39: (F2)[W11] A42: (G) [W7] 930610 (K39-((A39-$A$29)*24*60+(H39-$H$29)*60+(I39-$I$29))*$ B42: (G) [WIO] +B41+1 K$8) C42: (G) [W5] 121 039: (F2) [WIO] +$P$9+(N39-$0$9) D42: (F2) [W6] 34.489 P39: (F2) [W ll] E42: (G) [W5] 1 978031.85*(l+0.0053024*(@SIN(R39)*@SIN(R39))-0.00000 F42: (F2) [W6] 57.162 59*(@SDSr(2*R39)*@SIN(2*R39))) G42: (Fl) [W6] 0.5 210 H42: (G) [W3] 17 Q44: (F2) [W7] +044-P44 142: (G) [W4] 12 R44: (F6) [WIO] (E44+(F44/60))*$R$9 J42: (F2) [W ll] 1650.53 A45: (G) [W7] 930611 K42: (F2) [W9] ((J42-1600)* 1.02892+1647.24) B45: (G) [WIO] +B44+1 L42: (F2) [W8] 0.079 C45: (G) [W5] 121 M42: (F2) [W9] +K42+L42 D45: (F2) [W6] 32.187 N42: (F2) [W ll] E45: (G) [W5] 2 (K42-((A42-$A$29)*24*60+(H42-$H$29)*60+(I42-$I$29))*$ F45: (F2) [W6] 2.973 K$8) G45: (Fl) [W6] 0.6 042: (F2) [WIO] +$P$9+(N42-$0$9) H45: (G) [W3] 7 P42: (F2) [W ll] 145: (G) [W4] 51 978031.85*(l+0.0053024*(@SIN(R42)*@SIN(R42))-0.00000 J45: (F2) [W ll] 1641.48 59*(@SIN(2*R42)*@SIN(2*R42))) K45: (F2) [W9] Q42: (F2) [W7] +042-P42 ((J45-1600)*1.02892+1647.24) R42: (F6) [WIO] (E42+(F42/60))*$R$9 L45: (F2) [W8] 0.026 A43: (G) [W7] 930611 M45: (F2) [W9] +K45+L45 B43: (G) [WIO] 2014 N45: (F2) [W ll] C43: (G) [W5] 121 (K45-((A45-$A$29)*24*60+(H45-$H$29)* D43: (F2) [W6] 34.489 60+(I45-$I$29))*$K$8) E43: (G) [W5] 1 045: (F2) [WIO] +$P$9+(N45-$0$9) F43: (F2) [W6] 57.2 P45: (F2) [W ll] G43: (Fl) [W6] 0.5 978031.85*(1+0.0053024*(@SIN(R45)*@ H43: (G) [W3] 5 SIN(R45))-0.0000059*(@SIN(2*R45)*@SI 143: (G) [W4] 38 N(2*R45))) J43:(F2) [W ll] 1650.5 Q45: (F2) [W7] +045-P45 K43: (F2) [W9] ((J43-1600)* 1.02892+1647.24) R45: (F6) [WIO] (E45+(F45/60))*$R$9 L43: (F2) [W8] 0.084 A46: (G) [W7] 930611 M43: (F2) [W9] +K43+L43 B46: (G) [WIO] +B45+1 N43: (F2) [W ll] C46: (G) [W5] 121 (K43-((A43-$A$29)*24*60+(H43-$H$29)*60+(I43-$I$29))*$ D46: (F2) [W6] 32.186 K$8) E46: (G) [W5] 2 043: (F2) [WIO] +$P$9+(N43-$0$9) F46: (F2) [W6] 2.974 P43:(F2) [W ll] G46: (Fl) [W6] 0.75 978031.85*(l+0.0053024*(@SIN(R43)*@SIN(R43))-0.00000 H46: (G) [W3] 7 59*(@SIN(2*R43)*@SIN(2*R43))) 146: (G) [W4] 58 Q43: (F2) [W7] +043-P43 J46: (F2) [W ll] 1641.54 R43: (F6) [WIO] (E43+(F43/60))*$R$9 K46: (F2) [W9] A44: (G) [W7] 930611 ((J46-1600)*1.02892+1647.24) B44: (G) [WIO] +B43+1 L46: (F2) [W8] 0.022 C44: (G) [W5] 121 M46: (F2) [W9] +K46+L46 D44: (F2) [W6] 30.473 N46: (F2) [W ll] E44: (G) [W5] 1 (K46-((A46-$A$29)*24*60+(H46-$H$29)* F44: (F2) [W6] 56.9 60+(I46-$I$29))*$K$8) G44: (Fl) [W6] 0.5 046: (F2) [WIO] +$P$9+(N46-$0$9) H44: (G) [W3] 6 P46: (F2) [W ll] 144: (G) [W4] 41 978031.85*(1+0.0053024*(@SIN(R46)*@ J44: (F2) [W ll] 1658.465 SIN(R46))-0.0000059*(@SIN(2*R46)*@SI K44: (F2) [W9] ((J44-1600)* 1.02892+1647.24) N(2*R46))) L44: (F2) [W8] 0.059 Q46: (F2) [W7] +046-P46 M44: (F2) [W9] +K44+L44 R46: (F6) [WIO] (E46+(F46/60))*$R$9 N44: (F2) [W ll] A47: (G) [W7] 930611 (K44-((A44-$A$29)*24*60+(H44-$H$29)*60+(I44-$I$29))*$ B47: (G) [WIO] +B46+1 K$8) C47: (G) [W5] 121 044: (F2) [WIO] +$P$9+(N44-$0$9) D47: (F2) [W6] 32.363 P44: (F2) [W ll] E47: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R44)*@SIN(R44))-0.00000 F47: (F2) [W6] 6.216 59*(@SIN(2*R44)*@SIN(2*R44))) G47: (Fl) [W6] 0.75 211 H47: (G) [W3] 9 Q49: (F2) [W7] +049-P49 147: (G) [W4] 6 R49: (F6) [WIO] (E49+(F49/60))*$R$9 J47: (F2) [W ll] 1650.48 A50: (G) [W7] 930611 K47: (F2) [W9] ((J47-1600)*1.02892+1647.24) B50: (G) [WIO] +B49+1 L47: (F2) [W8] -0.005 C50: (G) [W5] 121 M47: (F2) [W9] +K47+L47 D50: (F2) [W6] 27.295 N47: (F2) [W ll] E50: (G) [W5] 1 (K47-((A47-$A$29)*24*60+(H47-$H$29)*60+(I47-$I$29))*$ F50: (F2) [W6] 59.865 K$8) G50: (Fl) [W6] 0.5 047: (F2) [WIO] +$P$9+(N47-$0$9) H50: (G) [W3] 13 P47: (F2) [W ll] 150: (G) [W4] 30 978031.85*(l+0.0053024*(@SIN(R47)*@SIN(R47))-0.00000 J50: (F2) [W ll] 1650.624 59*(@SIN(2*R47)*@SIN(2*R47))) K50: (F2) [W9] Q47: (F2) [W7] +047-P47 ((J50-1600)*1.02892+1647.24) R47: (F6) [WIO] (E47+(F47/60))*$R$9 L50: (F2) [W8] 0.028 A48: (G) [W7] 930611 M50: (F2) [W9] +K50+L50 B48: (G) [WIO] +B47+1 N50: (F2) [W ll] C48: (G) [W5] 121 (K50-((A50-$A$29)*24*60+(H50-$H$29)* D48: (F2) [W6] 30.27 60+(I50-$I$29))*$K$8) E48: (G) [W5] 2 050: (F2) [WIO] +$P$9+(N50-$O$9) F48: (F2) [W6] 2.568 P50: (F2) [W ll] G48: (Fl) [W6] -0.5 978031.85*(1+0.0053024*(@SIN(R50)*@ H48: (G) [W3] 10 SIN(R50))-0.0000059*(@SIN(2*R50)*@SI 148: (G) [W4] 14 N(2*R50))) J48: (F2) [W ll] 1645.694 Q50: (F2) [W7] +050-P50 K48: (F2) [W9] ((J48-1600)* 1.02892+1647.24) R50: (F6) [WIO] (E50+(F50/60))*$R$9 L48: (F2) [W8] -0.019 A51: (G) [W7] 930611 M48: (F2) [W9] +K48+L48 B51:(G)[W10]+B50+1 N48:(F2) [Wll] C51: (G) [W5] 121 (K48-((A48-$A$29)*24*60+(H48-$H$29)*60+(I48-$I$29))*$ D51: (F2) [W6] 28.443 K$8) E51: (G) [W5] 1 048: (F2) [WIO] +$P$9+(N48-$0$9) F51:(F2)[W6] 55.541 P48: (F2) [W ll] G51:(F1)[W6] 0.75 978031.85*(l+0.0053024*(@SIN(R48)*@SIN(R48))-0.00000 H51: (G) [W3] 14 59*(@SIN(2*R48)*@SIN(2*R48))) 151: (G) [W4] 42 Q48: (F2) [W7] +048-P48 J51:(F2) [W ll] 1660.463 R48: (F6) [WIO] (E48+(F48/60))*$R$9 K51: (F2) [W9] A49: (G) [W7] 930611 ((J51-1600)*1.02892+1647.24) B49: (G) [WIO] +B48+1 L51: (F2) [W8] 0.058 C49: (G) [W5] 121 M51: (F2) [W9] +K51+L51 D49: (F2) [W6] 25.675 N51:(F2) [Wll] E49: (G) [W5] 1 (K51-((A51-$A$29)*24*60+(H51-$H$29)* F49: (F2) [W6] 57.568 60+(I51-$I$29))*$K$8) G49: (Fl) [W6] 0.75 051: (F2) [WIO] +$P$9+(N51-$0$9) H49: (G) [W3] 11 P51:(F2) [Wll] 149: (G) [W4] 32 978031.85*(1+0.0053024*(@SIN(R51)*@ J49: (F2)[W11] 1654.962 SIN(R51))-0.0000059*(@SIN(2*R51)*@SI K49: (F2) [W9] ((J49-1600)* 1.02892+1647.24) N(2*R51))) L49: (F2) [W8] -0.014 Q51:(F2)[W7] +051-P51 M49: (F2) [W9] +K49+L49 R51: (F6) [WIO] (E51+(F51/60))*$R$9 N49: (F2) [W ll] A52: (G) [W7] 930611 (K49-((A49-$A$29)*24*60+(H49-$H$29)*60+(I49-$I$29))*$ B52: (G) [WIO]+B51+1 K$8) C52: (G) [W5] 121 049: (F2) [WIO] +$P$9+(N49-$0$9) D52: (F2) [W6] 26.62 P49: (F2) [W ll] E52: (G) [W5] 1 978031.85*(l+0.0053024*(@SIN(R49)*@SIN(R49))-0.00000 F52: (F2) [W6] 54.865 59*(@SIN(2*R49)*@SIN(2*R49))) G52: (Fl) [W6] 0.5 212 H52: (G) [W3] 15 Q54: (F2) [W7] +054-P54 152: (G) [W4] 13 R54: (F6) [WIO] (E54+(F54/60))*$R$9 J52: (F2) [W ll] 1663.96 A55: (G) [W7] 930611 K52: (F2) [W9] ((J52-1600)* 1.02892+1647.24) B55: (G) [WIO] +B54+1 L52: (F2) [W8] 0.068 C55: (G) [W5] 121 M52: (F2) [W9] +K52+L52 D55: (F2) [W6] 22.3 N52: (F2) [W ll] E55: (G) [W5] 1 (K52-((A52-$A$29)*24*60+(H52-$H$29)*60+(I52-$I$29))*$ F55: (F2) [W6] 58.716 K$8) G55: (Fl) [W6] 0.5 052: (F2) [WIO] +$P$9+(N52-$0$9) H55: (G) [W3] 17 P52: (F2) [W ll] 155: (G) [W4] 16 978031.85*(l+0.0053024*(@SIN(R52)*@SIN(R52))-0.00000 J55: (F2) [W ll] 1649.546 59*(@SIN(2*R52)*@SIN(2*R52))) K55: (F2) [W9] Q52: (F2) [W7] +052-P52 ((J55-1600)*1.02892+1647.24) R52: (F6) [WIO] (E52+(F52/60))*$R$9 L55: (F2) [W8] 0.083 A53: (G) [W7] 930611 M55: (F2) [W9] +K55+L55 B53: (G) [WIO] +B52+1 N55: (F2) [W ll] C53: (G) [W5] 121 (K55-((A55-$A$29)*24*60+(H55-$H$29)* D53: (F2) [W6] 23.718 60+(I55-$I$29))*$K$8) E53: (G) [W5] 1 055: (F2) [WIO] +$P$9+(N55-$0$9) F53: (F2) [W6] 54.46 P55: (F2) [W ll] G53: (Fl) [W6] 0.5 978031.85*(1+0.0053024*(@SIN(R55)*@ H53: (G) [W3] 15 SIN(R55))-0.0000059*(@SIN(2*R55)*@SI 153: (G) [W4] 50 N(2*R55))) J53:(F2) [W ll] 1661.51 Q55: (F2) [W7] +055-P55 K53: (F2) [W9] ((J53-1600)* 1.02892+1647.24) R55: (F6) [WIO] (E55+(F55/60))*$R$9 L53: (F2) [W8] 0.078 A56: (G) [W7] 930611 M53: (F2) [W9] +K53+L53 B56: (G) [WIO] 2001 N53:(F2) [Wll] C56: (G) [W5] 121 (K53-((A53-$A$29)*24*60+(H53-$H$29)*60+(I53-$I$29))*$ D56: (F2) [W6] 20.675 K$8) E56: (G) [W5] 2 053: (F2) [WIO] +$P$9+(N53-$0$9) F56: (F2) [W6] 0.34 P53: (F2) [W ll] G56: (Fl) [W6] 1.2 978031.85*(l+0.0053024*(@SIN(R53)*@SIN(R53))-0.00000 H56: (G) [W3] 17 59*(@SIN(2*R53)*@SIN(2*R53))) 156: (G) [W4] 45 Q53: (F2) [W7] +053-P53 J56: (F2) [W ll] 1647.723 R53: (F6) [WIO] (E53+(F53/60))*$R$9 K56: (F2) [W9] A54: (G) [W7] 930611 ((J56-1600)*1.02892+1647.24) B54: (G) [WIO] +B53+1 L56: (F2) [W8] 0.079 C54: (G) [W5] 121 M56: (F2) [W9] +K56+L56 D54: (F2) [W6] 22.3 N56: (F2) [W ll] E54: (G) [W5] 1 (K56-((A56-$A$29)*24*60+(H56-$H$29)* F54: (F2) [W6] 56.081 60+(I56-$I$29))*$K$8) G54: (Fl) [W6] 0.5 056: (F2) [WIO] +$P$9+(N56-$0$9) H54: (G) [W3] 16 P56: (F2) [W ll] 154: (G) [W4] 41 978031.85*(1+0.0053024*(@SIN(R56)*@ J54: (F2) [W ll] 1655.712 SIN(R56))-0.0000059*(@SIN(2*R56)*@SI K54: (F2) [W9] ((J54-1600)* 1.02892+1647.24) N(2*R56))) L54: (F2) [W8] 0.084 Q56: (F2) [W7] +056-P56 M54: (F2) [W9] +K54+L54 R56: (F6) [WIO] (E56+(F56/60))*$R$9 N54: (F2) [W ll] A57: (G) [W7] 930613 (K54-((A54-$A$29)*24*60+(H54-$H$29)*60+(I54-$I$29))*$ B57: (G) [WIO] 3001 K$8) C57: (G) [W5] 121 054: (F2) [WIO] +$P$9+(N54-$0$9) D57: (F2) [W6] 20.675 P54: (F2)[W11] E57: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R54)*@SIN(R54))-0.00000 F57: (F2) [W6] 0.34 59*(@SIN(2*R54)*@SIN(2*R54))) G57: (Fl) [W6] 1.2 213 H57: (G) [W3] 7 Q59: (F2) [W7] +059-P59 157: (G) [W4] 17 R59: (F6) [WIO] (E59+(F59/60))*$R$9 J57: (F2) [W ll] 1647.693 A60: (G) [W7] 930613 K57: (F2) [W9] ((J57-1600)* 1.02892+1647.24) B60: (G) [WIO] +B59+1 L57: (F2) [W8] 0.87 C60: (G) [W5] 121 M57: (F2) [W9] +K57+L57 D60: (F2) [W6] 44.928 N57: (F2) [W ll] E60: (G) [W5] 2 (K57-((A57-$A$29)*24*60+(H57-$H$29)*60+(I57-$I$29))*$ F60: (F2) [W6] 12.768 K$8) G60: (Fl) [W6] 0.6 057: (F2) [WIO] +$P$9+(N57-$0$9) H60: (G) [W3] 13 P57: (F2) [W ll] 160: (G) [W4] 33 978031.85*(l+0.0053024*(@SIN(R57)*@SIN(R57))-0.00000 J60: (F2) [W ll] 1649.237 59*(@SIN(2*R57)*@SIN(2*R57))) K60: (F2) [W9] Q57: (F2) [W7] +057-P57 ((J60-1600)*1.02892+1647.24) R57: (F6) [WIO] (E57+(F57/60))*$R$9 L60: (F2) [W8] -0.011 A58: (G) [W7] 930613 M60: (F2) [W9] +K60+L60 B58: (G) [WIO] 3027 N60: (F2) [W ll] C58: (G) [W5] 121 (K60-((A60-$A$29)*24*60+(H60-$H$29)* D58: (F2) [W6] 32.97 60+(I60-$I$29))*$K$8) E58: (G) [W5] 2 060: (F2) [WIO] +$P$9+(N60-$O$9) F58: (F2) [W6] 9.793 P60: (F2) [W ll] G58: (Fl) [W6] 0.75 978031.85*(1+0.0053024*(@SIN(R60)*@ H58: (G) [W3] 10 SIN(R60))-0.0000059*(@SIN(2*R60)*@SI 158: (G) [W4] 14 N(2*R60))) J58: (F2) [W ll] 1644.04 Q60: (F2) [W7] +060-P60 K58: (F2) [W9] ((J58-1600)* 1.02892+1647.24) R60: (F6) [WIO] (E60+(F60/60))*$R$9 L58: (F2) [W8] 0.027 A61: (G) [W7] 930613 M58: (F2) [W9] +K58+L58 B61:(G)[W10] +B60+1 N58:(F2) [W ll] C61: (G) [W5] 121 (K58-((A58-$A$29)*24*60+(H58-$H$29)*60+(I58-$I$29))*$ D61:(F2)[W6] 45.81 K$8) E61: (G) [W5] 2 058: (F2) [WIO] +$P$9+(N58-$0$9) F61: (F2) [W6] 15.54 P58: (F2) [W ll] G61:(F1)[W6] 0.5 978031.85*(l+0.0053024*(@SIN(R58)*@SIN(R58))-0.00000 H61: (G) [W3] 14 59*(@SIN(2*R58)*@SIN(2*R58))) 161: (G) [W4] 1 Q58: (F2) [W7] +058-P58 J61:(F2) [W ll] 1649.41 R58: (F6) [WIO] (E58+(F58/60))*$R$9 K61: (F2) [W9] A59: (G) [W7] 930613 ((J61-1600)*1.02892+1647.24) B59: (G) [WIO] +B58+1 L61: (F2) [W8] -0.006 C59: (G) [W5] 121 M61: (F2) [W9] +K61+L61 D59: (F2) [W6] 36.148 N61:(F2) [Wll] E59: (G) [W5] 2 (K61-((A61-$A$29)*24*60+(H61-$H$29)* F59: (F2) [W6] 12.52 60+(I61-$I$29))*$K$8) G59: (Fl) [W6] 0.3 061: (F2) [WIO] +$P$9+(N61-$0$9) H59: (G) [W3] 12 P61: (F2) [W ll] 159: (G) [W4] 10 978031.85*(1+0.0053024*(@SIN(R61)*@ J59: (F2) [W ll] 1653 SIN(R61))-0.0000059*(@SIN(2*R61)*@SI K59: (F2) [W9] ((J59-1600)*1.02892+1647.24) N(2*R61))) L59: (F2) [W8] -0.009 Q61: (F2) [W7] +061-P61 M59: (F2) [W9] +K59+L59 R61: (F6) [WIO] (E61+(F61/60))*$R$9 N59: (F2) [W ll] A62: (G) [W7] 930613 (K59-((A59-$A$29)*24*60+(H59-$H$29)*60+(I59-$I$29))*$ B62: (G) [WIO] +B61+1 K$8) C62: (G) [W5] 121 059: (F2) [WIO] +$P$9+(N59-$0$9) D62: (F2) [W6] 48.443 P59: (F2) [W ll] E62: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R59)*@SIN(R59))-0.00000 F62: (F2) [W6] 17.835 59*(@SIN(2*R59)*@SIN(2*R59))) G62: (Fl) [W6] 0.5 214 H62: (G) [W3] 14 Q64: (F2) [W7] +064-P64 162: (G) [W4] 35 R64: (F6) [WIO] (E64+(F64/60))*$R$9 J62: (F2) [W ll] 1644.95 A65: (G) [W7] 930614 K62: (F2) [W9] ((J62-1600)* 1.02892+1647.24) B65: (G) [WIO] "WOSU L62: (F2) [W8] 0.003 C65: (G) [W5] 121 M62: (F2) [W9] +K62+L62 D65: (F2) [W6] 50.045 N62: (F2) [W ll] E65: (G) [W5] 2 (K62-((A62-$A$29)*24*60+(H62-$H$29)*60+(I62-$I$29))*$ F65: (F2) [W6] 21.553 K$8) G65: (Fl) [W6] 5 062: (F2) [WIO] +$P$9+(N62-$0$9) H65: (G) [W3] 7 P62: (F2) [W ll] 165: (G) [W4] 27 978031.85*(l+0.0053024*(@SIN(R62)*@SIN(R62))-0.00000 J65: (F2) [W ll] 1644.583 59*(@SIN(2*R62)*@SIN(2*R62))) K65: (F2) [W9] Q62: (F2) [W7] +062-P62 ((J65-1600)*1.02892+1647.24) R62: (F6) [WIO] (E62+(F62/60))*$R$9 L65: (F2) [W8] 0.096 A63: (G) [W7] 930613 M65: (F2) [W9] +K65+L65 B63: (G) [WIO] +B62+1 N65:(F2) [Wll] C63: (G) [W5] 121 (K65-((A65-$A$29)*24*60+(H65-$H$29)* D63: (F2) [W6] 50.473 60+(I65-$I$29))*$K$8) E63: (G) [W5] 2 065: (F2) [WIO] +$P$9+(N65-$0$9) F63: (F2) [W6] 21.283 P65: (F2) [W ll] G63: (Fl) [W6] 0.5 978031.85*(1+0.0053024*(@SIN(R65)*@ H63: (G) [W3] 16 SIN(R65))-0.0000059*(@SIN(2*R65)*@SI 163: (G) [W4] 8 N(2*R65))) J63: (F2) [W ll] 1644.4 Q65: (F2) [W7] +065-P65 K63: (F2) [W9] ((J63-1600)*1.02892+1647.24) R65: (F6) [WIO] (E65+(F65/60))*$R$9 L63: (F2) [W8] 0.036 A66: (G) [W7] 930614 M63: (F2) [W9] +K63+L63 B66: (G) [WIO] 4033 N63: (F2) [W ll] C66: (G) [W5] 121 (K63-((A63-$A$29)*24*60+(H63-$H$29)*60+(I63-$I$29))*$ D66: (F2) [W6] 52.97 K$8) E66: (G) [W5] 2 063: (F2) [WIO] +$P$9+(N63-$0$9) F66: (F2) [W6] 25.135 P63: (F2) [W ll] G66: (Fl) [W6] 0.5 978031.85*(l+0.0053024*(@SIN(R63)*@SIN(R63))-0.00000 H66: (G) [W3] 8 59*(@SIN(2*R63)*@SIN(2*R63))) 166: (G) [W4] 37 Q63: (F2) [W7] +063-P63 J66: (F2) [W ll] 1653.182 R63: (F6) [WIO] (E63+(F63/60))*$R$9 K66: (F2) [W9] A64: (G) [W7] 930613 ((J66-1600)*1.02892+1647.24) B64: (G) [WIO] 'WOSU L66: (F2) [W8] 0.09 C64: (G) [W5] 121 M66: (F2) [W9] +K66+L66 D64: (F2) [W6] 50.045 N66: (F2) [W ll] E64: (G) [W5] 2 (K66-((A66-$A$29)*24*60+(H66-$H$29)* F64: (F2) [W6] 21.553 60+(I66-$I$29))*$K$8) G64: (Fl) [W6] 5 066: (F2) [WIO] +$P$9+(N66-$0$9) H64: (G) [W3] 20 P66: (F2) [W ll] 164: (G) [W4] 1 978031.85*(1+0.0053024*(@SIN(R66)*@ J64: (F2) [W ll] 1644.565 SIN(R66))-0.0000059*(@SIN(2*R66)*@SI K64: (F2) [W9] ((J64-1600)* 1.02892+1647.24) N(2*R66))) L64: (F2) [W8] 0.079 Q66: (F2) [W7] +066-P66 M64: (F2) [W9] +K64+L64 R66: (F6) [WIO] (E66+(F66/60))*$R$9 N64: (F2) [W ll] A67: (G) [W7] 930614 (K64-((A64-$A$29)*24*60+(H64-$H$29)*60+(I64-$I$29))*$ B67: (G) [WIO] +B66+1 K$8) C67: (G) [W5] 121 064: (F2) [WIO] +$P$9+(N64-$0$9) D67: (F2) [W6] 55.54 P64: (F2) [W ll] E67: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R64)*@SIN(R64))-0.00000 F67: (F2) [W6] 28.542 59*(@SIN(2*R64)*@SIN(2*R64))) G67: (Fl) [W6] 0.5 215 H67: (G) [W3] 9 Q69: (F2) [W7] +069-P69 167: (G) [W4] 34 R69: (F6) [WIO] (E69+(F69/60))*$R$9 J67: (F2) [W ll] 1660.93 A70: (G) [W7] 930614 K67: (F2) [W9] ((J67-1600)*1.02892+1647.24) B70: (G) [WIO] +B69+1 L67: (F2) [W8] 0.072 C70: (G) [W5] 122 M67: (F2) [W9] +K67+L67 D70: (F2) [W6] 0.574 N67: (F2) [W ll] E70: (G) [W5] 2 (K67-((A67-$A$29)*24*60+(H67-$H$29)*60+(I67-$I$29))*$ F70: (F2) [W6] 40.405 K$8) G70: (Fl) [W6] 0.75 067: (F2) [WIO] +$P$9+(N67-$0$9) H70: (G) [W3] 13 P67: (F2) [W ll] 170: (G) [W4] 30 978031.85*(l+0.0053024*(@SIN(R67)*@SIN(R67))-0.00000 J70: (F2) [W ll] 1677.253 59*(@SIN(2*R67)*@SIN(2*R67))) K70: (F2) [W9] Q67: (F2) [W7] +067-P67 ((J70-1600)*1.02892+1647.24) R67: (F6) [WIO] (E67+(F67/60))*$R$9 L70: (F2) [W8] -0.021 A68: (G) [W7] 930614 M70: (F2) [W9] +K70+L70 B68: (G) [WIO] +B67+1 N70: (F2) [W ll] C68: (G) [W5] 121 (K70-((A70-$A$29)*24*60+(H70-$H$29)* D68: (F2) [W6] 57.97 60+(I70-$I$29))*$K$8) E68: (G) [W5] 2 070: (F2) [WIO] +$P$9+(N70-$O$9) F68: (F2) [W6] 32.652 P70: (F2) [W ll] G68: (Fl) [W6] 0.3 978031.85*(1+0.0053024*(@SIN(R70)*@ H68: (G) [W3] 10 SIN(R70))-0.0000059*(@SIN(2*R70)*@SI 168: (G) [W4] 17 N(2*R70))) J68: (F2) [W ll] 1670.142 Q70: (F2) [W7] +070-P70 K68: (F2) [W9] ((J68-1600)*1.02892+1647.24) R70: (F6) [WIO] (E70+(F70/60))*$R$9 L68: (F2) [W8] 0.053 A71: (G) [W7] 930614 M68: (F2) [W9] +K68+L68 B71: (G) [WIO] +B70+1 N68: (F2) [W ll] C71: (G) [W5] 122 (K68-((A68-$A$29)*24*60+(H68-$H$29)*60+(I68-$I$29))*$ D71: (F2) [W6] 3.78 K$8) E71: (G) [W5] 2 068: (F2) [WIO] +$P$9+(N68-$0$9) F71: (F2) [W6] 45.608 P68:(F2) [Wll] G71: (Fl) [W6] 0.5 978031.85*(l+0.0053024*(@SIN(R68)*@SIN(R68))-0.00000 H71: (G) [W3] 14 59*(@SIN(2*R68)*@SIN(2*R68))) 171: (G) [W4] 55 Q68: (F2) [W7] +068-P68 J71:(F2)[W11] 1683.19 R68: (F6) [WIO] (E68+(F68/60))*$R$9 K71: (F2) [W9] A69: (G) [W7] 930614 ((J71-1600)*1.02892+1647.24) B69: (G) [WIO] +B68+1 L71: (F2) [W8] -0.017 C69: (G) [W5] 121 M71: (F2) [W9] +K71+L71 D69: (F2) [W6] 59.73 N71:(F2) [Wll] E69: (G) [W5] 2 (K71-((A71-$A$29)*24*60+(H71-$H$29)* F69: (F2) [W6] 36.789 60+(I71-$I$29))*$K$8) G69: (Fl) [W6] 0.5 071: (F2) [WIO] +$P$9+(N71-$0$9) H69: (G) [W3] 12 P71: (F2) [W ll] 169: (G) [W4] 39 978031.85*(1+0.0053024*(@SIN(R71)*@ J69: (F2) [W ll] 1680.16 SIN(R71))-0.0000059*(@SIN(2*R71)*@SI K69: (F2) [W9] ((J69-1600)* 1.02892+1647.24) N(2*R71))) L69: (F2) [W8] -0.011 Q71: (F2) [W7] +071-P71 M69: (F2) [W9] +K69+L69 R71: (F6) [WIO] (E71+(F71/60))*$R$9 N69: (F2) [W ll] A72: (G) [W7] 930614 (K69-((A69-$A$29)*24*60+(H69-$H$29)*60+(I69-$I$29))*$ B72: (G) [WIO] +B71+1 K$8) C72: (G) [W5] 122 069: (F2) [WIO] +$P$9+(N69-$0$9) D72: (F2) [W6] 8.066 P69: (F2) [W ll] E72: (G) [W5] 2 978031.85*(1+0.0053024*(@SIN(R69)*@SIN(R69))-0.00000 F72: (F2) [W6] 47.329 59*(@SIN(2*R69)*@SIN(2*R69))) G72: (Fl) [W6] -0.5 216 H72: (G) [W3] 15 Q74: (F2) [W7] +074-P74 172: (G) [W4] 46 R74: (F6) [WIO] (E74+(F74/60))*$R$9 J72: (F2) [W ll] 1676.4 A75: (G) [W7] 930615 K72: (F2) [W9] ((J72-1600)* 1.02892+1647.24) B75: (G) [WIO] 5040 L72: (F2) [W8] -0.001 C75: (G) [W5] 122 M72: (F2) [W9] +K72+L72 D75: (F2) [W6] 10.8 N72: (F2) [W ll] E75: (G) [W5] 2 (K72-((A72-$A$29)*24*60+(H72-$H$29)*60+(I72-$I$29))*$ F75: (F2) [W6] 51.75 K$8) G75: (Fl) [W6] 1 072: (F2) [WIO] +$P$9+(N72-$0$9) H75: (G) [W3] 7 P72: (F2) [W ll] 175: (G) [W4] 43 978031.85*(l+0.0053024*(@SIN(R72)*@SIN(R72))-0.00000 J75: (F2) [W ll] 1702.343 59*(@SIN(2*R72)*@SIN(2*R72))) K75: (F2) [W9] Q72: (F2) [W7] +072-P72 ((J75-1700)*1.02891+1750.13) R72: (F6) [WIO] (E72+(F72/60))*$R$9 L75: (F2) [W8] 0.102 A73: (G) [W7] 930614 M75: (F2) [W9] +K75+L75 B73: (G) [WIO] "LAILIA N75: (F2) [W ll] C73: (G) [W5] 122 (K75-((A75-$A$29)*24*60+(H75-$H$29)* D73: (F2) [W6] 9.315 60+(I75-$I$29))*$K$8) E73: (G) [W5] 2 075: (F2) [WIO] +$P$9+(N75-$0$9) F73: (F2) [W6] 48.443 P75: (F2) [W ll] G73: (Fl) [W6] 5 978031.85*(1+0.0053024*(@SIN(R75)*@ H73: (G) [W3] 17 SIN(R75))-0.0000059*(@SIN(2*R75)*@SI 173: (G) [W4] 31 N(2*R75))) J73:(F2) [W ll] 1687.542 Q75: (F2) [W7] +075-P75 K73: (F2) [W9] ((J73-1600)* 1.02892+1647.24) R75: (F6) [WIO] (E75+(F75/60))*$R$9 L73: (F2) [W8] 0.045 A76: (G) [W7] 930615 M73: (F2) [W9] +K73+L73 B76: (G) [WIO] +B75+1 N73:(F2) [Wll] C76: (G) [W5] 122 (K73-((A73-$A$29)*24*60+(H73-$H$29)*60+(I73-$I$29))*$ D76: (F2) [W6] 11.61 K$8) E76: (G) [W5] 2 073: (F2) [WIO] +$P$9+(N73-$0$9) F76: (F2) [W6] 52.695 P73: (F2) [W ll] G76: (Fl) [W6] 2 978031.85*(l+0.0053024*(@SIN(R73)*@SIN(R73))-0.00000 H76: (G) [W3] 8 59*(@SIN(2*R73)*@SIN(2*R73))) 176: (G) [W4] 9 Q73: (F2) [W7] +073-P73 J76: (F2) [W ll] 1703.56 R73: (F6) [WIO] (E73+(F73/60))*$R$9 K76: (F2) [W9] A74: (G) [W7] 930615 ((J76-1700)*1.02891+1750.13) B74: (G) [WIO] "LAILIA L76: (F2) [W8] 0.107 C74: (G) [W5] 122 M76: (F2) [W9] +K76+L76 D74: (F2) [W6] 9.315 N76: (F2) [W ll] E74: (G) [W5] 2 (K76-((A76-$A$29)*24*60+(H76-$H$29)* F74: (F2) [W6] 48.443 60+(I76-$I$29))*$K$8) G74: (Fl) [W6] 5 076: (F2) [WIO] +$P$9+(N76-$0$9) H74: (G) [W3] 6 P76: (F2) [W ll] 174: (G) [W4] 43 978031.85*(1+0.0053024*(@SIN(R76)*@ J74: (F2) [W ll] 1687.58 SIN(R76))-0.0000059*(@SIN(2*R76)*@SI K74: (F2) [W9] ((J74-1600)* 1.02892+1647.24) N(2*R76))) L74: (F2) [W8] 0.078 Q76: (F2) [W7] +076-P76 M74: (F2) [W9] +K74+L74 R76: (F6) [WIO] (E76+(F76/60))*$R$9 N74: (F2) [W ll] A77: (G) [W7] 930615 (K74-((A74-$A$29)*24*60+(H74-$H$29)*60+(I74-$I$29))*$ B77: (G) [WIO] +B76+1 K$8) C77: (G) [W5] 122 074: (F2) [WIO] +$P$9+(N74-$0$9) D77: (F2) [W6] 11.138 P74: (F2) [W ll] E77: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R74)*@SIN(R74))-0.00000 F77: (F2) [W6] 49.725 59*(@SIN(2*R74)*@SIN(2*R74))) G77: (Fl) [W6] 0.5 217 H77: (G) [W3] 8 Q79: (F2) [W7] +079-P79 177: (G) [W4] 48 R79: (F6) [WIO] (E79+(F79/60))*$R$9 J77: (F2) [W ll] 1698.185 A80: (G) [W7] 930615 K77: (F2) [W9] ((J77-1600)* 1.02892+1647.24) B80: (G) [WIO] 5044 L77: (F2) [W8] 0.108 C80: (G) [W5] 122 M77: (F2) [W9] +K77+L77 D80: (F2) [W6] 1.08 N77: (F2) [W ll] E80: (G) [W5] 2 (K77-((A77-$A$29)*24*60+(H77-$H$29)*60+(I77-$I$29))*$ F80: (F2) [W6] 43.375 K$8) G80: (Fl) [W6] 0.75 077: (F2) [WIO] +$P$9+(N77-$0$9) H80: (G) [W3] 11 P77: (F2) [W ll] 180: (G) [W4] 7 978031.85*(l+0.0053024*(@SIN(R77)*@SIN(R77))-0.00000 J80: (F2) [W ll] 1663.68 59*(@SIN(2*R77)*@SIN(2*R77))) K80: (F2) [W9] Q77: (F2) [W7] +077-P77 ((J80-1600)*1.02892+1647.24) R77: (F6) [WIO] (E77+(F77/60))*$R$9 L80: (F2) [W8] 0.057 A78: (G) [W7] 930615 M80: (F2) [W9] +K80+L80 B78: (G) [WIO] 5039 N80: (F2) [W ll] C78: (G) [W5] 122 (K80-((A80-$A$29)*24*60+(H80-$H$29)* D78: (F2) [W6] 8.066 60+(I80-$I$29))*$K$8) E78: (G) [W5] 2 080: (F2) [WIO] +$P$9+(N80-$O$9) F78: (F2) [W6] 47.329 P80: (F2) [W ll] G78: (Fl) [W6] 1.5 978031.85*(1+0.0053024*(@SIN(R80)*@ H78: (G) [W3] 9 SIN(R80))-0.0000059*(@SIN(2*R80)*@SI 178: (G) [W4] 30 N(2*R80))) J78: (F2) [W ll] 1676.15 Q80: (F2) [W7] +080-P80 K78: (F2) [W9] ((J78-1600)* 1.02892+1647.24) R80: (F6) [WIO] (E80+(F80/60))*$R$9 L78: (F2) [W8] 0.101 A81: (G) [W7] 930615 M78: (F2) [W9] +K78+L78 B81: (G) [WIO] "BUNGKU N78:(F2)[W11] C81: (G) [W5] 121 (K78-((A78-$A$29)*24*60+(H78-$H$29)*60+(I78-$I$29))*$ D81: (F2) [W6] 58.038 K$8) E81: (G) [W5] 2 078: (F2) [WIO] +$P$9+(N78-$0$9) F81: (F2) [W6] 32.97 P78:(F2) [Wll] G81: (Fl) [W6] 3 978031.85*(l+0.0053024*(@SIN(R78)*@SIN(R78))-0.00000 H81: (G) [W3] 16 59*(@SIN(2*R78)*@SIN(2*R78))) 181: (G) [W4] 52 Q78: (F2) [W7] +078-P78 J81:(F2) [W ll] 1669.97 R78: (F6) [WIO] (E78+(F78/60))*$R$9 K81: (F2) [W9] A79: (G) [W7] 930615 ((J81-1600)*1.02892+1647.24) B79: (G) [WIO] 5043 L81: (F2) [W8] -0.006 C79: (G) [W5] 122 M81:(F2)[W9] +K81+L81 D79: (F2) [W6] 5.198 N81:(F2)[W11] E79: (G) [W5] 2 (K81-((A81-$A$29)*24*60+(H81-$H$29)* F79: (F2) [W6] 47.16 60+(I81-$I$29))*$K$8) G79: (Fl) [W6] 0.5 081: (F2) [WIO] +$P$9+(N81-$0$9) H79: (G) [W3] 10 P81: (F2) [W ll] 179: (G) [W4] 11 978031.85*(1+0.0053024*(@SIN(R81)*@ J79: (F2) [W ll] 1684.09 SIN(R81))-0.0000059*(@SIN(2*R81)*@SI K79: (F2) [W9] ((J79-1600)* 1.02892+1647.24) N(2*R81))) L79: (F2) [W8] 0.086 Q81:(F2)[W7] +081-P81 M79: (F2) [W9] +K79+L79 R81: (F6) [WIO] (E81+(F81/60))*$R$9 N79: (F2) [W ll] A82: (G) [W7] 930616 (K79-((A79-$A$29)*24*60+(H79-$H$29)*60+(I79-$I$29))*$ B82: (G) [WIO] "BUNGKU K$8) C82: (G) [W5] 121 079: (F2) [WIO] +$P$9+(N79-$0$9) D82: (F2) [W6] 58.038 P79: (F2) [W ll] E82: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R79)*@SIN(R79))-0.00000 F82: (F2) [W6] 32.97 59*(@SIN(2*R79)*@SIN(2*R79))) G82: (Fl) [W6] 3 218 H82: (G) [W3] 6 Q84: (F2) [W7] +084-P84 182: (G) [W4] 6 R84: (F6) [WIO] (E84+(F84/60))*$R$9 J82: (F2) [W ll] 1669.92 A85: (G) [W7] 930616 K82: (F2) [W9] ((J82-1600)*1.02892+1647.24) B85: (G) [WIO] 6047 L82: (F2) [W8] 0.028 C85: (G) [W5] 121 M82: (F2) [W9] +K82+L82 D85: (F2) [W6] 38.578 N82: (F2) [W ll] E85: (G) [W5] 2 (K82-((A82-$A$29)*24*60+(H82-$H$29)*60+(I82-$I$29))*$ F85: (F2) [W6] 11.249 K$8) G85: (Fl) [W6] -0.5 082: (F2) [WIO] +$P$9+(N82-$0$9) H85: (G) [W3] 15 P82:(F2) [W ll] 185: (G) [W4] 50 978031.85*(l+0.0053024*(@SIN(R82)*@SIN(R82))-0.00000 J85:(F2) [W ll] 1651.932 59*(@SIN(2*R82)*@SIN(2*R82))) K85: (F2) [W9] Q82: (F2) [W7] +082-P82 ((J85-1600)*1.02892+1647.24) R82: (F6) [WIO] (E82+(F82/60))*$R$9 L85: (F2) [W8] -0.054 A83: (G) [W7] 930616 M85: (F2) [W9] +K85+L85 B83: (G) [WIO] 6045 N85:(F2) [Wll] C83: (G) [W5] 121 (K85-((A85-$A$29)*24*60+(H85-$H$29)* D83: (F2) [W6] 52.093 60+(I85-$I$29))*$K$8) E83: (G) [W5] 2 085: (F2) [WIO] +$P$9+(N85-$0$9) F83: (F2) [W6] 24.055 P85: (F2) [W ll] G83: (Fl) [W6] 0.25 978031.85*(1+0.0053024*(@SIN(R85)*@ H83: (G) [W3] 8 SIN(R85))-0.0000059*(@SIN(2*R85)*@SI 183: (G) [W4] 44 N(2*R85))) J83:(F2)[W11] 1646.31 Q85: (F2) [W7] +085-P85 K83: (F2) [W9] ((J83-1600)*1.02892+1647.24) R85: (F6) [WIO] (E85+(F85/60))*$R$9 L83:(F2) [W8] 0.116 A86: (G) [W7] 930616 M83: (F2) [W9] +K83+L83 B86: (G) [WIO] "UNGKAYA N83:(F2) [Wll] 086: (G) [W5] 121 (K83-((A83-$A$29)*24*60+(H83-$H$29)*60+(I83-$I$29))*$ D86: (F2) [W6] 35.405 K$8) E86: (G) [W5] 2 083: (F2) [WIO] +$P$9+(N83-$0$9) F86: (F2) [W6] 12.903 P83:(F2) [Wll] G86: (Fl) [W6] '* 978031.85*(l+0.0053024*(@SIN(R83)*@SIN(R83))-0.00000 H86: (G) [W3] 17 59*(@SIN(2*R83)*@SIN(2*R83))) 186: (G) [W4] 2 Q83: (F2) [W7] +083-P83 J86: (F2)[W11] 1640.46 R83: (F6) [WIO] (E83+(F83/60))*$R$9 K86: (F2) [W9] A84: (G) [W7] 930616 ((J86-1600)*1.02892+1647.24) B84: (G) [WIO] 6046 L86: (F2) [W8] -0.034 C84: (G) [W5] 121 M86: (F2) [W9] +K86+L86 D84: (F2) [W6] 40.743 N86: (F2) [W ll] E84: (G) [W5] 2 (K86-((A86-$A$29)*24*60+(H86-$H$29)* F84: (F2) [W6] 10.405 60+(I86-$I$29))*$K$8) G84: (Fl) [W6] 0.75 086: (F2) [WIO] +$P$9+(N86-$0$9) H84: (G) [W3] 15 P86: (F2) [W ll] 184: (G) [W4] 13 978031.85*(1+0.0053024*(@SIN(R86)*@ J84: (F2) [W ll] 1655.06 SIN(R86))-0.0000059*(@SIN(2*R86)*@SI K84: (F2) [W9] ((J84-1600)* 1.02892+1647.24) N(2*R86))) L84: (F2) [W8] -0.054 Q86: (F2) [W7] +086-P86 M84: (F2) [W9] +K84+L84 R86: (F6) [WIO] (E86+(F86/60))*$R$9 N84: (F2) [W ll] A87: (G) [W7] 930617 (K84-((A84-$A$29)*24*60+(H84-$H$29)*60+(I84-$I$29))*$ B87: (G) [WIO] "UNGKAYA K$8) 087: (G) [W5] 121 084: (F2) [WIO] +$P$9+(N84-$0$9) D87: (F2) [W6] 35.405 P84: (F2) [W ll] E87: (G) [W5] 2 978031.85*(l+0.0053024*(@SIN(R84)*@SIN(R84))-0.00000 F87: (F2) [W6] 12.903 59*(@SIN(2*R84)*@SIN(2*R84))) G87: (Fl) [W6] '* 219 H87: (G) [W3] 6 Q89: (F2) [W7] +089-P89 187: (G) [W4] 33 R89: (F6) [WIO] (E89+(F89/60))*$R$9 J87: (F2) [W ll] 1640.398 A90: (G) [W7] 930619 K87: (F2) [W9] ((J87-1600)* 1.02892+1647.24) B90: (G) [WIO] "HM-LUW L87: (F2) [W8] -0.013 C90: (G) [W5] 122 M87: (F2) [W9] +K87+L87 D90: (F2) [W6] 47.43 N87: (F2) [W ll] E90: (G) [W5] 0 (K87-((A87-$A$29)*24*60+(H87-$H$29)*60+(I87-$I$29))*$ F90: (F2) [W6] 57.03 K$8) G90: (Fl) [W6] 2.5 087: (F2) [WIO] +$P$9+(N87-$0$9) H90: (G) [W3] 17 P87: (F2) [W ll] 190: (G) [W4] 44 978031.85*(l+0.0053024*(@SIN(R87)*@SIN(R87))-0.00000 J90: (F2) [W ll] 1645.686 59*(@SIN(2*R87)*@SIN(2*R87))) K90: (F2) [W9] Q87: (F2) [W7] +087-P87 ((J90-1600)*1.02892+1647.24) R87: (F6) [WIO] (E87+(F87/60))*$R$9 L90: (F2) [W8] -0.092 A88: (G) [W7] 930617 M90: (F2) [W9] +K90+L90 B88: (G) [WIO] 7001 N90: (F2) [W ll] C88: (G) [W5] 121 (K90-((A90-$A$29)*24*60+(H90-$H$29)* D88: (F2) [W6] 20.675 60+(I90-$I$29))*$K$8) E88: (G) [W5] 2 090: (F2) [WIO] +$P$9+(N90-$O$9) F88: (F2) [W6] 0.34 P90: (F2) [W ll] G88:(F1)[W6] 1.2 978031.85*(1+0.0053024*(@SIN(R90)*@ H88: (G) [W3] 9 SIN(R90))-0.0000059*(@SIN(2*R90)*@SI 188: (G) [W4] 25 N(2*R90))) J88: (F2) [W ll] 1647.437 Q90: (F2) [W7] +090-P90 K88: (F2) [W9] ((J88-1600)*1.02892+1647.24) R90: (F6) [WIO] (E90+(F90/60))*$R$9 L88: (F2) [W8] 0.127 A91: (G) [W7] 930620 M88: (F2) [W9] +K88+L88 B91: (G) [WIO] "BB-A/P N88:(F2) [W ll] C91: (G) [W5] 122 (K88-((A88-$A$29)*24*60+(H88-$H$29)*60+(I88-$I$29))*$ D91: (F2) [W6] 44.73 K$8) E91: (G) [W5] 1 088: (F2) [WIO] +$P$9+(N88-$0$9) F91: (F2) [W6] 3.038 P88:(F2) [W ll] G91: (Fl) [W6] '* 978031.85*(l+0.0053024*(@SIN(R88)*@SIN(R88))-0.00000 H91: (G) [W3] 6 59*(@SIN(2*R88)*@SIN(2*R88))) 191: (G) [W4] 22 Q88: (F2) [W7] +088-P88 J91:(F2) [W ll] 1655.52 R88: (F6) [WIO] (E88+(F88/60))*$R$9 K91: (F2) [W9] A89: (G) [W7] 930619 ((J91-1600)*1.02892+1647.24) B89: (G) [WIO] "RATA L91: (F2) [W8] -0.09 C89: (G) [W5] 122 M91: (F2) [W9] +K91+L91 D89: (F2) [W6] 5.603 N91:(F2) [Wll] E89: (G) [W5] 1 (K91-((A91-$A$29)*24*60+(H91-$H$29)* F89: (F2) [W6] 36.953 60+(I91-$I$29))*$K$8) G89: (Fl) [W6] 0.1 091: (F2) [WIO] +$P$9+(N91-$0$9) H89: (G) [W3] 13 P91: (F2) [W ll] 189: (G) [W4] 5 978031.85*(1+0.0053024*(@SIN(R91)*@ J89: (F2) [W ll] 1677.05 SIN(R91))-0.0000059*(@SIN(2*R91)*@SI K89: (F2) [W9] ((J89-1600)* 1.02892+1647.24) N(2*R91))) L89: (F2) [W8] 0.103 Q91: (F2) [W7] +091-P91 M89: (F2) [W9] +K89+L89 R91: (F6) [WIO] (E91+(F91/60))*$R$9 N89: (F2) [W ll] A92: (G) [W7] 930621 (K89-((A89-$A$29)*24*60+(H89-$H$29)*60+(I89-$I$29))*$ B92: (G) [WIO] "PL-A/P K$8) C92: (G) [W5] 119 089: (F2) [WIO] +$P$9+(N89-$0$9) D92: (F2) [W6] 53 P89: (F2) [W ll] E92: (G) [W5] 0 978031.85*(l+0.0053024*(@SIN(R89)*@SIN(R89))-0.00000 F92: (F2) [W6] 52.235 59*(@SIN(2*R89)*@SIN(2*R89))) G92: (Fl) [W6] 87 220 H92: (G) [W3] 13 192: (G) [W4] 35 J92: (F2) [W ll] 1633.16 K92: (F2) [W9] ((J92-1600)* 1.02892+1647.24) L92: (F2) [W8] 0.15 M92: (F2) [W9] +K92+L92 N92: (F2) [W ll] (K92-((A92-$A$29)*24*60+(H92-$H$29)*60+(I92-$I$29))*$ K$8) 092: (F2) [WIO] +$P$9+(N92-$0$9) P92: (F2) [W ll] 978031.85*(l+0.0053024*(@SIN(R92)*@SIN(R92))-0.00000 59*(@SIN(2*R92)*@SIN(2*R92))) Q92: (F2) [W7] +092-P92 R92: (F6) [WIO] (E92+(F92/60))*$R$9 A93: (G) [W7] 930621 B93: (G) [WIO] "UP-A/P C93: (G) [W5] 119 D93: (F2) [W6] 33 E93: (G) [W5] 5 F93: (F2) [W6] 4 G93: (Fl) [W6] 32 H93: (G) [W3] 16 193: (G) [W4] 3 J93:(F2) [W ll] 1722.955 K93: (F2) [W9] ((J93-1700)* 1.02891+1750.13) L93: (F2) [W8] 0.028 M93: (F2) [W9] +K93+L93 N93:(F2) [Wll] (K93-((A93-$A$29)*24*60+(H93-$H$29)*60+(I93-$I$29))*$ K$8) 093: (F2) [WIO] +$P$9+(N93-$0$9) P93:(F2) [W ll] 978031.85*(l+0.0053024*(@SIN(R93)*@SIN(R93))-0.00000 59*(@SIN(2*R93)*@SIN(2*R93))) Q93: (F2) [W7] +093-P93 R93: (F6) [WIO] (E93+(F93/60))*$R$9

221 Appendix C Gravity Data Sorong Fault Zone Project 1987-1993

C.1 SORONG FAULT ZONE PROJECT : Gravity Expedition 1987 Survey Areas: West and South Halmahera, Temate, Tidore and Bacan Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) goôs(mGal) g„(mGal) jR/4(mGal)

TTEOl 127.381800 0.807727 0.0 978185.1 978032.9 152.2 TTE02 127.366520 0.842273 0.0 978180.4 978033.0 147.4 TTE03 127.347640 0.855000 0.0 978166.1 978033.0 133.1 TTE04 127.316180 0.844091 0.0 978163.2 978033.0 130.2 TTE05 127.304490 0.843182 1.0 978178.6 978033.0 145.8 TTE06 127.291910 0.820455 4.0 978182.2 978032.9 150.1 TTE07 127.290110 0.797727 3.0 978178.3 978032.9 146.0 TTE08 127.294610 0.780455 0.0 978175.2 978032.8 142.4 TTE09 127.303600 0.758636 0.0 978172.9 978032.8 140.1 TTEIO 127.320670 0.752273 3.0 978173.2 978032.7 141.1 TTEll 127.344940 0.757727 0.0 978171.0 978032.8 138.2 TTE12 127.361120 0.760455 0.0 978171.0 978032.8 138.2 TTE13 127.372810 0.765909 0.0 978172.8 978032.8 140.0 TTDOl 127.382700 0.733182 0.0 978174.7 978032.7 142.0 TTD02 127.379100 0.716818 0.0 978178.0 978032.7 145.3 TTD03 127.371010 0.697727 0.0 978177.6 978032.6 145.0 TTD04 127.360220 0.673182 1.5 978163.0 978032.6 130.7 TTD05 127.364720 0.658636 1.5 978161.6 978032.5 129.4 TTD06 127.367420 0.642273 0.0 978159.9 978032.5 127.4 TTD07 127.376400 0.629546 5.0 978158.7 978032.5 127.2 TTD08 127.399780 0.623182 3.0 978157.0 978032.5 125.1 TTD09 127.418650 0.625000 2.0 978157.6 978032.5 125.5 TTDIO 127.431240 0.637727 2.0 978157.8 978032.5 125.7 T T D ll 127.439330 0.645000 1.5 978156.8 978032.5 124.6 TTD12 127.444720 0.656818 1.5 978154.0 978032.5 121.8 TTD13 127.452810 0.674091 0.8 978152.8 978032.6 120.4 TTD14 127.452810 0.701364 2.0 978156.7 978032.6 124.5 TTD15 127.453710 0.716818 1.0 978159.9 978032.7 127.4 TTD16 127.444720 0.739546 1.5 978164.8 978032.7 132.4 TTD17 127.424070 0.745909 2.5 978168.6 978032.7 136.4 TTD18 127.408760 0.746818 0.5 978173.7 978032.7 141.1 HALOl 127.552610 0.738601 0.0 978157.6 978032.7 124.9 HAL02 127.548070 0.691648 0.0 978167.0 978032.6 134.4 HAL03 127.499090 0.631151 1.0 978186.5 978032.5 154.2 HAL04 127.528120 0.604966 1.0 978190.8 978032.4 158.6 HALOS 127.529020 0.564334 1.0 978179.5 978032.4 147.3 HAL06 127.548070 0.527314 0.0 978179.2 978032.3 146.9 HAL07 127.560770 0.510158 0.8 978185.6 978032.3 153.5 HALOS 127.560770 0.473138 0.0 978184.5 978032.2 152.3 HAL09 127.574380 0.433409 0.0 978180.1 978032.1 148.0 HALIO 127.572560 0.402709 2.0 978175.1 978032.1 143.4 H A L ll 127.614290 0.392777 1.5 978169.1 978032.1 137.3

222 Appendix C Gravity Data Sorong Fault Zone Project 1987-1993

SORONG FAULT ZONE PROJECT Gravity Expedition 1987 Survey Areas: West and South Halmahera, Temate, Tidore and Bacan Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) ^oôj(mGal) ^„(mGal) &4(mGal)

HAL12 127.609750 0.357562 0.0 978166.9 978032.1 134.8 HAL13 127.645120 0.353047 0.5 978157.0 978032.0 125.1 HAL14 127.719500 0.330474 1.5 978142.8 978032.0 111.1 HAL15 127.719500 0.287133 0.5 978150.2 978032.0 118.3 HAL16 127.708620 0.244695 0.8 978155.2 978031.9 123.5 HAL17 127.698640 0.205869 0.5 978162.1 978031.9 130.3 HAL18 127.685940 0.164334 1.0 978169.0 978031.9 137.3 HAL19 127.692290 0.123702 2.0 978166.2 978031.9 134.7 HAL20 127.691190 0.028894 1.5 978149.7 978031.9 118.1 HAL21 127.706800 0.074041 0.8 978156.6 978031.9 124.9 HAL22 127.695920 0.020768 0.0 978149.1 978031.9 117.2 HAL23 127.693860 0.066817 1.0 978148.6 978031.9 116.9 HAL24 127.683180 0.118284 1.5 978147.1 978031.9 115.5 HAL25 127.677840 0.161625 1.0 978159.0 978031.9 127.3 HAL26 127.662700 0.206772 1.0 978176.6 978031.9 144.9 HAL27 127.668040 0.226637 0.5 978182.8 978031.9 151.0 HAL28 127.684960 0.263657 0.5 978179.9 978032.0 148.0 HAL29 127.729460 0.305192 1.0 978189.2 978032.0 157.4 SALOl 127.735690 0.358465 0.0 978195.4 978032.1 163.3 SAL02 127.724120 0.402709 0.0 978196.4 978032.1 164.3 HAL30 127.775750 0.334989 0.0 978177.6 978032.0 145.6 HAL31 127.822040 0.347630 1.0 978168.0 978032.0 136.2 HAL32 127.854970 0.366591 2.0 978162.7 978032.1 131.0 HAL33 127.890570 0.425282 1.0 978159.4 978032.1 127.5 HAL34 127.967130 0.586907 1.0 978160.6 978032.4 128.4 HAL35 127.942200 0.530926 0.5 978148.0 978032.3 115.8 HAL36 127.926180 0.494808 1.0 978149.3 978032.2 117.3 BACOl 127.654690 0.441535 0.5 978186.0 978032.2 153.9 BAC02 127.619980 0.418059 0.5 978170.7 978032.1 138.7 BAC03 127.590600 0.363883 1.5 978173.1 978032.1 141.3 BAC04 127.557670 0.318736 1.0 978176.1 978032.0 144.3 BAC05 127.524740 0.306998 0.5 978177.8 978032.0 145.9 BAC06 127.490910 0.344018 0.5 978194.8 978032.0 162.9 BAC07 127.474000 0.373815 0.5 978198.9 978032.1 166.9 BAC08 127.449080 0.423476 1.0 978192.6 978032.1 160.7 BAC09 127.407240 0.374718 0.0 978205.1 978032.1 173.0 BAG 10 127.376980 0.334086 0.0 978212.0 978032.0 180.0 BAG 11 127.328020 0.338601 0.0 978203.9 978032.0 171.9 BAG 12 127.336140 0.385553 1.0 978207.0 978032.1 175.1 BAG13 127.301320 0.434312 0.0 978207.0 978032.1 174.9 BAG14 127.289740 0.479458 1.0 978197.4 978032.2 165.4 BAG 15 127.309330 0.521896 0.3 978184.9 978032.3 152.7

223 Appendix C Gravity Data Sorong Fault Zone Project 1987-1993

SORONG FAULT ZONE PROJECT Gravity Expedition 1987 Survey Areas: West and South Halmahera, Temate, Tidore and Bacan Longitude and Latitude are expressed in decimal degrees Station Longitude (East) Latitude Elevation(m) ^ofo(mOal) ^«(mOal) A4(mGal)

BAG 16 127.339590 0.549887 0.0 978183.8 978032.3 151.5 BAC17 127.359170 0.588713 0.0 978174.3 978032.3 142.0 BAG 18 127.404570 0.628442 0.5 978166.5 978032.5 134.1 BAG19 127.472220 0.637472 1.0 978148.7 978032.5 116.4 BAG20 127.453530 0.699774 0.5 978139.1 978032.6 106.6 BAG21 127.433940 0.754853 0.8 978142.0 978032.7 109.5 BAG22 127.456200 0.797291 1.0 978146.1 978032.8 113.5 BAG23 127.496250 0.810835 0.5 978140.8 978032.9 108.0 BAG24 127.549660 0.786456 0.8 978132.5 978032.8 99.9 BAG25 127.602180 0.768397 0.8 978134.5 978032.8 101.9 BAG26 127.642230 0.751242 1.3 978148.4 978032.7 116.0 BAG27 127.652020 0.794582 0.4 978159.8 978032.8 127.1 BAG28 127.675170 0.833409 0.8 978170.4 978032.9 137.7 BAG29 127.719670 0.859537 0.8 978176.5 978033.0 143.7 BAG30 127.770410 0.872235 2.0 978177.2 978033.0 144.6 HAL37 127.984930 0.616704 1.8 978174.1 978032.4 142.1 HAL38 128.022310 0.694357 0.0 978178.9 978032.6 146.3 HAL39 128.057920 0.715124 0.5 978178.8 978032.7 146.2 HAL40 128.125570 0.734086 1.0 978175.5 978032.7 143.0 HAL41 128.206570 0.764786 0.8 978151.5 978032.8 118.9 HAL42 128.088180 0.838826 0.3 978164.6 978033.0 131.7 HAL43 128.162950 0.750339 0.5 978168.9 978032.7 136.3 HAL44 128.247510 0.796388 0.0 978157.1 978032.8 124.3 HAL45 128.260860 0.829797 0.2 978167.7 978032.9 134.8 HAL46 128.225260 0.849661 0.0 978179.2 978033.0 146.2 HAL47 128.274220 0.875847 0.0 978177.7 978033.1 144.6 HAL48 128.303590 0.860497 0.5 978172.2 978033.0 139.3 HAL49 128.348990 0.874944 0.5 978171.2 978033.1 138.2 HAL50 128.403280 0.892099 0.5 978164.1 978033.1 131.1 HAL51 128.208350 0.705192 0.8 978143.7 978032.6 111.3 HAL52 128.179860 0.651919 0.5 978146.8 978032.5 114.4 HAL53 128.164730 0.618510 0.8 978148.0 978032.5 115.7 HAL54 128.132690 0.579684 1.0 978144.9 978032.4 112.7 HAL55 128.097970 0.520993 1.5 978147.5 978032.3 115.5 HAL56 128.073050 0.468623 0.0 978149.9 978032.2 117.7 HAL57 128.049910 0.425282 1.3 978148.9 978032.1 117.1 HAL58 128.030320 0.386456 0.5 978153.2 978032.1 121.2 HAL59 128.015190 0.345824 0.0 978154.5 978032.0 122.5 HAL60 128.000060 0.304289 2.0 978157.0 978032.0 125.4 HAL61 127.881860 0.053273 1.5 978159.1 978031.9 127.5 HAL62 127.916330 0.225734 1.5 978172.4 978031.9 140.8 HAL63 127.872790 0.332280 1.5 978156.2 978032.0 124.5

224 Appendix C Gravity Data Sorong Fault Zone Project 1987-1993

SORONG FAULT ZONE PROJECT Gravity Expedition 1987 Survey Areas: West and South Halmahera, Temate, Tidore and Bacan Longitude and Latitude are expressed in decimal degrees Station Longitude (East) Latitude Elevation(m) ^oAj(mGal) ^«(mGal) &4(mGal)

HAL64 127.928120 0.465914 1.0 978183.7 978032.2 151.7 HAL65 128.088660 0.458691 1.3 978154.0 978032.2 122.1 HAL66 128.047850 0.046862 0.5 978164.1 978032.2 132.0 HAL67 127.990700 0.470429 0.0 978173.3 978032.2 141.1 HAL68 127.970750 0.481264 0.3 978177.7 978032.2 145.6 HAL69 127.894560 0.433409 0.0 978168.7 978032.1 136.6 HAL70 127.888210 0.354853 0.3 978154.9 978032.0 123.0 HAL71 127.907260 0.277201 0.0 978163.9 978032.0 131.9 HAL72 127.890930 0.101129 0.0 978174.1 978031.9 142.2 HAL73 127.898190 -0.018962 0.5 978157.9 978031.9 126.1 HAL74 127.924400 0.080361 0.0 978156.9 978031.9 125.0 HAL75 127.943090 0.117382 0.2 978161.5 978031.9 129.6 HAL76 127.969800 0.207675 0.3 978163.4 978031.9 131.6 HAL77 127.975140 0.251919 0.3 978160.8 978031.9 129.0 HAL78 128.193880 0.422573 1.0 978130.8 978032.1 98.9 HAL79 128.497730 0.352154 0.8 978154.8 978032.0 123.0 HAL80 128.543060 0.326862 0.5 978161.7 978032.0 129.8 HAL81 128.582990 0.316930 0.3 978157.6 978032.0 125.7 HAL82 128.475960 0.391874 0.3 978157.1 978032.1 125.1 HAL83 128.453290 0.401806 0.3 978149.5 978032.1 117.5 HAL84 128.410660 0.390068 0.0 978132.7 978032.1 100.6 HAL85 128.542180 0.398194 0.0 978131.8 978032.1 99.7 HAL86 128.285490 0.391874 0.1 978125.8 978032.1 93.7 HAL87 128.238320 0.405418 0.0 978130.5 978032.1 98.4 HAL88 128.121320 0.460497 0.5 978157.0 978032.2 124.9 HAL89 128.154880 0.455079 0.3 978143.3 978032.2 111.2 HAL90 128.735370 0.316027 2.0 978182.0 978032.0 150.4 HAL91 127.894560 1.173815 1.3 978170.9 978034.0 137.2 HAL92 128.679140 0.433409 1.5 978172.7 978032.1 140.9 HAL93 128.663720 0.354853 0.5 978172.0 978032.0 140.1 HAL94 128.706350 0.322348 0.0 978170.7 978032.0 138.7 HAL95 128.803400 0.306998 0.2 978187.3 978032.0 155.3 HAL96 128.833330 0.290745 0.5 978181.4 978032.0 149.5 HAL97 128.867800 0.271783 0.0 978170.5 978032.0 138.5 HAL98 128.664630 0.493002 0.1 978165.6 978032.2 133.4

225 C.2 SORONG FAULT ZONE PROJECT : Gravity Expedition 1989 Survey Areas: South Halmahera, Bacan, Kasiruta, Obi, Sulabesi and Mangole Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) ^ofo(mGal) ^„(mGal) R/4(mGal)

89000 127.698700 -0.027160 1.4 978149.3 978031.9 117.7 89001 127.461600 -0.019830 1.2 978202.1 978031.9 170.5 89002 127.434700 -0.077000 1.0 978201.2 978031.9 169.5 89003 127.422000 -0.031670 2.0 978203.4 978031.9 171.9 89004 127.461600 -0.019830 1.2 978202.1 978031.9 170.5 89005 127.465100 -0.024300 0.6 978200.3 978031.9 168.6 89006 127.453500 -0.122200 0.7 978192.3 978031.9 160.6 89007 127.411600 -0.075100 0.6 978199.1 978031.9 167.4 89008 127.391500 -0.269800 0.7 978184.6 978032.0 152.8 89009 127.340000 -0.333000 0.6 978178.8 978032.0 146.9 89010 127.383300 -0.436500 1.2 978180.0 978032.2 148.1 89011 127.434700 -0.340500 1.8 978177.7 978032.0 146.0 89012 127.692300 -0.117700 1.2 978146.9 978031.9 115.3 89013 127.688700 -0.153000 1.2 978153.4 978031.9 121.7 89014 127.683300 -0.193800 1.5 978158.5 978031.9 126.9 89015 127.663500 -0.225500 1.2 978177.9 978031.9 146.2 89016 127.690500 -0.274300 1.3 978182.9 978032.0 151.2 89017 127.695800 -0.095000 1.4 978145.7 978031.9 114.1 89018 127.698700 -0.027160 1.4 978149.5 978031.9 117.9 89019 127.863300 -0.368300 2.0 978162.5 978032.1 130.8 89020 127.933300 -0.496700 1.0 978147.5 978032.2 115.5 89021 127.661700 -0.445000 0.5 978185.0 978032.2 152.9 89022 127.696800 -0.474500 1.2 978185.7 978032.2 153.7 89023 127.677800 -0.501600 0.6 978176.1 978032.3 144.0 89024 127.663500 -0.539800 1.0 978158.0 978032.3 125.9 89025 127.629200 -0.567000 0.8 978149.9 978032.4 117.7 89026 127.600300 -0.648500 1.0 978137.8 978032.5 105.5 89027 127.475000 -0.638300 1.0 978147.7 978032.5 115.4 89028 127.262500 -0.367700 1.3 978229.8 978032.1 198.0 89029 127.250000 -0.511500 0.8 978229.0 978032.3 196.9 89030 127.279700 -0.297000 1.2 978219.7 978032.0 187.9 89031 127.240000 -0.267200 1.4 978235.3 978032.0 203.6 89032 127.193200 -0.274300 0.6 978246.5 978032.0 214.6 89033 127.123000 -0.221800 1.2 978264.0 978031.9 232.3 89034 127.084200 -0.272500 1.0 978260.9 978032.0 229.1 89035 127.059800 -0.291670 0.8 978248.7 978032.0 216.9 89036 127.128300 -0.295100 0.8 978250.8 978032.0 219.0 89037 127.128300 -0.341500 0.4 978237.1 978032.0 205.1 89038 127.112200 -0.400300 0.3 978224.6 978032.1 192.6 89039 127.113800 -0.498200 0.8 978213.6 978032.2 181.5 89040 127.098800 -0.542500 0.6 978204.9 978032.3 172.7 89041 127.233600 -0.552500 1.2 978185.2 978032.3 153.1 89042 127.208500 -0.534300 0.8 978196.9 978032.3 164.8 89043 127.261600 -0.503500 0.6 978197.1 978032.3 165.0 89044 127.263500 -0.440100 0.4 978214.4 978032.2 182.3 89045 127.244500 -0.621300 0.4 978179.1 978032.5 146.7

226 SORONG FAULT ZONE PROJECT Gravity Expedition 1989 Survey Areas: South Halmahera, Bacan, Kasiruta, Obi, Sulabesi and Mangole Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) ^^^^(mGal) gm(mGal) BA(mGal)

89046 127.322000 -0.639500 0.6 978166.9 978032.5 134.5 89047 127.365300 -0.638500 1.1 978167.8 978032.5 135.5 89048 127.493200 -0.829700 2.1 978145.0 978032.9 112.5 89049 127.575200 -0.794300 2.5 978177.0 978032.9 144.6 89050 127.724700 -0.875000 1.8 978176.8 978033.1 144.1 89051 127.764300 -0.888500 1.6 978178.5 978033.1 145.7 89052 127.821200 -0.873200 0.8 978189.4 978033.1 156.5 89053 127.858000 -0.849500 0.6 978186.5 978033.0 153.6 89054 127.893170 -0.810670 0.5 978176.4 978032.9 143.6 89055 127.864300 -0.770800 1.2 978171.4 978032.8 138.8 89056 127.832800 -0.735500 0.6 978149.0 978032.7 116.4 89057 127.766200 -0.713670 1.1 978142.8 978032.7 110.4 89058 127.721160 -0.717300 0.9 978144.6 978032.7 112.1 89059 127.664300 -0.730000 0.7 978144.7 978032.7 112.1 89060 127.648200 -0.686500 1.6 978136.6 978032.6 104.3 89061 127.636300 -0.652200 0.2 978140.0 978032.5 107.5 89062 127.613000 -0.580300 0.9 978144.0 978032.4 111.8 89063 127.644700 -1.335800 1.3 978148.1 978034.7 113.7 89064 127.576800 -1.358500 0.9 978160.0 978034.8 125.4 89065 127.538300 -1.406800 1.1 978144.9 978035.0 110.1 89066 127.502200 -1.431000 0.8 978121.1 978035.1 86.1 89067 127.420600 -1.419700 1.2 978123.8 978035.1 89.0 89068 127.418500 -1.454700 1.1 978116.3 978035.2 81.3 89069 127.337000 -1.429800 0.6 978125.0 978035.1 90.0 89070 127.280500 -1.427500 1.3 978119.8 978035.1 85.0 89071 127.305300 -1.389000 0.8 978129.4 978034.9 94.6 89072 127.368700 -1.368700 0.9 978137.2 978034.8 102.5 89073 127.404800 -1.504500 1.4 978136.7 978035.5 101.5 89074 127.391300 -1.540600 1.5 978124.6 978035.6 89.3 89075 127.380000 -1.540600 1.8 978127.0 978035.6 91.7 89076 127.404800 -1.662800 2.1 978135.4 978036.3 99.6 89077 127.447800 -1.696800 1.5 978134.9 978036.4 98.8 89078 127.486300 -1.730600 1.4 978137.6 978036.6 101.3 89079 127.543000 -1.735200 1.0 978141.0 978036.6 104.6 89080 127.590500 -1.730670 1.2 978140.0 978036.6 103.6 89081 127.638000 -1.728500 0.4 978141.0 978036.6 104.5 89082 127.393700 -1.581300 0.7 978127.2 978035.8 91.5 89083 127.667300 -1.703500 1.3 978142.6 978036.5 106.4 89084 127.746500 -1.685500 3.5 978143.8 978036.4 108.1 89085 127.812200 -1.696700 1.7 978157.5 978036.4 121.4 89086 127.877700 -1.683200 0.9 978169.0 978036.4 132.8 89087 127.914000 -1.687700 0.8 978174.6 978036.4 138.4 89088 127.963700 -1.694500 0.6 978182.5 978036.4 146.2 89089 128.009000 -1.721200 2.0 978186.3 978036.6 150.1 89090 127.633300 -1.822300 1.8 978167.2 978037.1 130.4 89091 127.576800 -1.831300 1.3 978158.4 978037.2 121.5

227 SORONG FAULT ZONE PROJECT Gravity Expedition 1989 Survey Areas: South Halmahera, Bacan, Kasiruta, Obi, Sulabesi and Mangole Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) gg^mGal) ^„(mGal) &4(mGal)

89092 127.601600 -1.847200 1.1 978164.8 978037.3 127.7 89093 127.565500 -1.867500 0.8 978163.5 978037.4 126.3 89094 128.040600 -1.718200 0.8 978184.5 978036.5 148.1 89095 128.079200 -1.720500 0.6 978162.4 978036.6 126.0 89096 128.128000 -1.688800 0.5 978161.9 978036.4 125.6 89097 128.165000 -1.639000 0.3 978152.0 978036.1 115.9 89098 128.149300 -1.593800 0.4 978152.8 978035.9 117.0 89099 128.106300 -1.559800 0.7 978147.3 978035.7 111.7 89100 128.045200 -1.548500 1.0 978157.5 978035.7 122.0 89101 127.988700 -1.506700 0.6 978158.1 978035.5 122.8 89102 127.947800 -1.470500 1.2 978155.6 978035.3 120.5 89103 127.900300 -1.432000 0.3 978156.8 978035.1 121.7 89104 127.828000 -1.429800 0.7 978169.4 978035.1 134.4 89105 127.701300 -1.333700 1.5 978150.5 978034.7 116.1 89106 127.748800 -1.356300 1.1 978147.5 978034.8 112.9 89107 127.782700 -1.399200 0.3 978160.5 978035.0 125.6 89108 127.640200 -1.221700 1.2 978122.5 978034.2 88.5 89109 127.538300 -1.171800 0.3 978108.0 978034.0 74.0 89110 127.502200 -1.194500 1.2 978112.5 978034.1 78.6 89111 127.468200 -1.223800 1.1 978104.4 978034.2 70.4 89112 127.515800 -1.251000 0.8 978093.5 978034.3 59.3 89113 127.588200 -1.257800 0.3 978104.5 978034.4 70.2 89114 127.434300 -1.201300 2.5 978093.2 978034.1 59.5 89115 127.427500 -1.167300 0.4 978102.5 978034.0 68.6 89116 127.395800 -1.147000 1.1 978069.1 978033.9 35.4 89117 127.414000 -1.212700 1.6 978087.3 978034.2 53.4 89118 125.981600 -2.058700 2.0 978332.5 978038.6 294.3 89119 125.959200 -2.119800 1.8 978330.7 978039.0 292.1 89120 125.961500 -2.171800 0.6 978326.2 978039.4 287.0 89121 125.975000 -2.210300 0.8 978316.9 978039.6 277.4 89122 125.997700 -2.259000 1.3 978299.7 978040.0 260.0 89123 125.972800 -2.004500 0.2 978337.5 978038.2 299.3 89124 125.891300 -1.990800 0.2 978346.5 978038.2 308.4 89125 125.871000 -2.029300 1.1 978362.4 978038.4 324.2 89126 125.855200 -2.095000 1.2 978352.6 978038.8 314.0 89127 125.882300 -2.148200 0.7 978342.3 978039.2 303.2 89128 125.880000 -2.191200 1.8 978305.0 978039.5 265.9 89129 125.904800 -2.238700 0.5 978306.5 978039.8 266.8 89130 125.932000 -2.288300 1.1 978302.6 978040.2 262.6 89131 125.950200 -2.328000 0.7 978292.6 978040.5 252.3 89132 125.947800 -2.382300 0.8 978286.1 978040.9 245.4 89133 125.970500 -2.429800 0.7 978280.9 978041.2 239.8 89134 126.009000 -2.466000 1.2 978272.9 978041.5 231.6 89135 125.936500 -1.923000 0.6 978327.6 978037.7 290.0 89136 125.902700 -1.932000 1.1 978335.1 978037.8 297.5 89137 125.857300 -1.898200 2.4 978326.1 978037.6 289.0

228 SORONG FAULT ZONE PROJECT Gravity Expedition 1989 Survey Areas: South Halmahera, Bacan, Kasiruta, Obi, Sulabesi and Mangole Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) g^éjCrnOal) ^„(mOal) &4(mGal)

89138 125.800800 -1.914000 0.4 978329.5 978037.7 291.9 89139 125.744300 -1.923000 1.6 978333.0 978037.7 295.6 89140 125.678700 -1.927500 1.8 978339.0 978037.8 301.6 89141 125.619800 -1.925300 0.7 978345.2 978037.7 307.6 89142 125.567800 -1.934300 0.8 978356.3 978037.8 318.7 89143 125.490800 -1.934300 0.2 978305.8 978037.8 268.0 89144 125.425300 -1.952300 1.9 978351.1 978037.9 313.6 89145 125.436500 -1.900300 1.4 978342.8 978037.6 305.5 89146 125.359700 -1.864200 0.2 978329.0 978037.4 291.7 89147 125.325700 -1.855200 0.6 978290.9 978037.3 253.7 89148 125.368600 -1.796300 0.5 978276.2 978037.0 239.3 89149 125.404800 -1.785000 1.5 978263.7 978036.9 227.1 89150 125.450200 -1.791800 1.3 978270.4 978037.0 233.7 89151 125.484200 -1.786200 0.5 978262.8 978036.9 226.0 89152 125.536200 -1.788300 0.4 978265.8 978036.9 228.9 89153 125.595000 -1.811000 1.3 978281.4 978037.1 244.6 89154 125.658300 -1.822300 0.4 978287.9 978037.1 250.8 89155 125.733000 -1.813300 3.2 978281.9 978037.1 245.4 89156 125.795200 -1.806500 0.7 978274.3 978037.0 237.4 89157 125.874300 -1.802000 0.9 978271.9 978037.0 235.1 89158 125.943300 -1.792800 1.2 978265.7 978037.0 229.0 89159 126.033800 -1.795200 2.3 978258.5 978037.0 222.0 89160 126.108500 -1.806500 0.8 978255.7 978037.0 218.8 89161 126.180800 -1.808700 3.6 978252.5 978037.1 216.2 89162 126.265800 -1.813300 2.4 978245.6 978037.1 209.0 89163 126.335800 -1.820000 0.6 978235.4 978037.1 198.4 89164 126.283800 -1.851700 1.3 978262.6 978037.3 225.5 89165 126.218200 -1.865300 1.1 978280.8 978037.4 243.6 89166 126.164000 -1.881200 0.9 978285.7 978037.5 248.4 89167 126.092700 -1.876700 1.1 978293.0 978037.5 255.8 89168 126.011200 -1.906000 0.4 978306.2 978037.6 268.6

229 C.3 SORONG FAULT ZONE PROJECT : Gravity Expedition 1990 Survey Areas: North Halmahera and Morotai Longitude and Latitude are expressed in decimal degrees Note: Elevation data are not available but stations were all located at or close to sea level

Station Longitude (East) Latitude Elevation(m) gotXmGal) g«(mGal) A4(mGal)

90001 127.735770 0.462900 978170.0 978032.2 137.8 90002 127.374000 0.482500 978167.0 978032.2 134.8 90003 127.381500 0.509400 978172.5 978032.3 140.2 90004 127.398000 0.520600 978168.4 978032.3 136.1 90005 127.363800 0.517700 978162.9 978032.3 130.6 90006 127.732400 0.517000 978157.9 978032.3 125.6 90007 127.306800 0.516000 978148.6 978032.3 116.3 90008 127.595900 0.544700 978143.5 978032.3 111.2 90009 127.300000 0.563600 978143.0 978032.4 110.6 90010 128.000700 0.529800 978148.8 978032.3 116.5 90011 127.300000 0.591300 978140.5 978032.4 108.1 90012 127.273400 1.009100 978149.9 978033.5 116.4 90013 127.253500 1.019600 978156.1 978033.5 122.6 90014 127.221900 1.034500 978166.4 978033.6 132.8 90015 127.249100 1.060800 978153.5 978033.6 119.9 90016 127.255700 1.093600 978147.8 978033.8 114.0 90017 127.242100 1.124000 978153.8 978033.9 119.9 90018 127.267500 1.158200 978154.0 978034.0 120.0 90019 127.288200 1.180800 978152.2 978034.1 118.1 90020 127.294300 1.208500 978150.0 978034.2 115.8 90021 127.288200 1.238500 978157.8 978034.3 123.5 90022 127.308900 1.255500 978161.3 978034.4 126.9 90023 127.318100 1.286600 978173.4 978034.5 138.9 90024 127.312700 1.319100 978185.1 978034.6 150.5 90025 127.314200 1.348000 978192.6 978034.7 157.9 90026 127.312000 1.370000 978195.8 978034.8 161.0 90027 127.336400 1.395300 978197.8 978034.9 162.9 90028 127.329400 1.422100 978219.0 978035.1 183.9 90029 127.304300 1.413200 978221.0 978035.0 186.0 90030 127.290700 1.413200 978223.7 978035.0 188.7 90031 127.338500 1.443300 978222.0 978035.2 186.8 90032 127.349600 1.462200 978225.7 978035.3 190.4 90033 127.371000 1.481400 978231.7 978035.3 196.4 90034 127.183700 1.518200 978230.6 978035.5 195.1 90035 127.402300 1.536600 978222.3 978035.6 186.7 90036 127.414600 1.558900 978217.8 978035.7 182.1 90037 127.429400 1.571100 978215.3 978035.8 179.5 90038 127.446400 1.581900 978216.2 978035.8 180.4 90039 127.454300 1.293000 978214.1 978034.5 179.6 90040 127.470600 2.012800 978203.5 978038.3 165.2 90041 127.481200 2.029700 978198.4 978038.4 160.0 90042 127.469300 2.067600 978197.3 978038.7 158.6 90043 127.462900 2.094600 978206.0 978038.8 167.2 90044 127.000000 2.000000 978203.8 978038.2 165.6 230 SORONG FAULT ZONE PROJECT Gravity Expedition 1990 Survey Areas: North Halmahera and Morotai Longitude and Latitude are expressed in decimal degrees Note: Elevation data are not available but stations were all located at or close to sea level

Station Longitude (East) Latitude Elevation(m) gotXmGal) ^„(mGal) A4(mGal)

90045 127.474400 2.133800 978204.1 978039.1 165.0 90046 127.489400 2.149400 978204.8 978039.2 165.6 90047 127.455000 2.153700 978195.9 978039.2 156.7 90048 127.502300 2.056100 978193.8 978038.6 155.2 90049 127.523000 2.071100 978204.8 978038.7 166.1 90050 127.544300 2.094600 978207.0 978038.8 168.2 90051 127.570500 2.118300 978203.7 978039.0 164.7 90052 127.463900 2.110900 978190.9 978038.9 152.0 90053 127.551800 2.121000 978183.2 978039.0 144.2 90054 127.554100 2.177100 978180.7 978039.4 141.3 90055 128.103800 2.202100 978189.1 978039.6 149.5 90056 128.106600 2.223800 978190.7 978039.7 151.0 90057 128.094300 2.248100 978183.7 978039.9 143.8 90058 128.178100 2.250800 978191.6 978039.9 151.7 90059 128.191800 2.281200 978184.8 978040.1 144.7 90060 128.207700 2.292400 978185.0 978040.2 144.8 90061 128.244000 2.318900 978185.5 978040.4 145.1 90062 128.254500 2.349600 978180.2 978040.6 139.6 90063 128.239600 2.352700 978181.0 978040.7 140.3 90064 128.312900 2.349300 978187.3 978040.6 146.7 90065 128.395000 2.237900 978190.6 978039.8 150.8 90066 128.332600 2.063500 978197.5 978038.6 158.9 90067 128.285500 2.038500 978171.2 978038.5 132.7 90068 128.228600 2.032400 978171.3 978038.4 132.9 90069 128.194100 2.021600 978155.3 978038.4 116.9 90070 128.162900 1.596800 978135.8 978035.9 99.9 90071 127.557900 1.589500 978149.2 978035.9 113.3 90072 127.521000 1.562400 978162.1 978035.7 126.4 90073 127.506000 1.519700 978165.1 978035.5 129.6 90074 127.502000 1.519700 978149.2 978035.5 113.7 90075 127.502700 1.496000 978142.4 978035.4 107.0 90076 127.533900 1.482500 978141.2 978035.3 105.9 90077 127.551200 1.475300 978140.1 978035.3 104.8 90078 127.568600 1.482500 978127.3 978035.3 92.0 90079 127.586200 1.467000 978126.5 978035.3 91.2 90080 128.005200 1.431800 978124.5 978035.1 89.4 90081 128.003400 1.410900 978127.0 978035.0 92.0 90082 127.448000 0.489300 978157.0 978032.2 124.8 90083 127.431300 0.508900 978158.6 978032.3 126.3 90084 127.388200 0.546100 978163.7 978032.3 131.4 90085 127.376000 0.569000 978164.6 978032.4 132.2 90086 127.486200 1.002700 978160.8 978033.5 127.3 90087 127.491400 1.016500 978161.9 978033.5 128.4 90088 127.509100 1.023300 978138.7 978033.5 105.2 231 SORONG FAULT ZONE PROJECT Gravity Expedition 1990 Survey Areas: North Halmahera and Morotai Longitude and Latitude are expressed in decimal degrees Note: Elevation data are not available but stations were all located at or close to sea level

Station Longitude (East) Latitude Elevation(m) gofa(°iGal) ^„(mOal) R/4(mOal)

90089 127.520700 1.025300 978123.3 978033.5 89.8 90090 127.561300 1.050700 978142.7 978033.6 109.1 90091 127.576200 1.060800 978132.9 978033.6 99.3 90092 127.592500 1.082500 978126.0 978033.7 92.3 90093 128.017700 1.086500 978112.0 978033.7 78.3 90094 128.058600 1.124400 978111.9 978033.9 78.0 90095 128.075800 1.156600 978113.6 978034.0 79.6 90096 128.087300 1.181200 978110.0 978034.1 75.9 90097 128.104300 1.165600 978121.7 978034.0 87.7 90098 127.593700 1.229200 978110.0 978034.3 75.7 90099 127.582300 1.174000 978168.0 978034.0 134.0 90100 127.570600 1.013500 978169.1 978033.5 135.6 90101 127.555200 0.290700 978169.3 978032.0 137.3 90102 127.551100 0.260200 978147.8 978032.0 115.8 90103 127.555200 0.229200 978149.9 978031.9 118.0 90104 127.536500 0.204800 978150.6 978031.9 118.7 90105 127.521300 0.190600 978149.7 978031.9 117.8 90106 127.497900 0.177100 978153.0 978031.9 121.1 90107 128.173800 0.174400 978145.0 978031.9 113.1 90108 128.040200 1.065000 978172.8 978033.7 139.1 90109 128.062500 1.070600 978165.6 978033.7 131.9 90110 128.082800 1.073700 978150.5 978033.7 116.8 90111 128.062000 1.073000 978114.8 978033.7 81.1 90112 128.082800 1.080400 978130.1 978033.7 96.4 90113 128.098300 1.106100 978120.7 978033.8 86.9 90114 128.116700 1.127400 978138.1 978033.9 104.2 90115 128.103800 1.146400 978138.6 978033.9 104.7 90116 128.076700 1.148000 978151.9 978033.9 118.0 90117 128.098600 1.164500 978149.7 978034.0 115.7 90118 128.076300 1.176200 978157.0 978034.1 122.9 90119 128.076300 1.193300 978173.6 978034.1 139.5 90120 128.086400 1.213600 978173.3 978034.2 139.1 90121 128.097700 1.232500 978163.0 978034.3 128.7 90122 128.149100 1.250100 978158.7 978034.3 124.4 90123 128.173800 1.258200 978143.8 978034.4 109.4 90124 128.188700 1.267700 978127.4 978034.4 93.0 90125 128.200900 1.273800 978121.9 978034.4 87.5 90126 128.224000 1.302000 978113.7 978034.5 79.2 90127 128.244100 1.313700 978115.8 978034.6 81.2 90128 128.296300 1.323700 978123.0 978034.6 88.4 90129 128.365800 1.343300 978135.5 978034.7 100.8 90130 128.430300 1.318400 978144.9 978034.6 110.3 90131 128.416700 1.304100 978131.6 978034.6 97.0 90132 128.407200 1.277800 978115.2 978034.4 80.8 232 SORONG FAULT ZONE PROJECT Gravity Expedition 1990 Survey Areas; North Halmahera and Morotai Longitude and Latitude are expressed in decimal degrees Note: Elevation data are not available but stations were all located at or close to sea level

Station Longitude (East) Latitude Elevation(m) gobs(jxiGa\) ^„(mOal) R/4(mGal)

90133 128.425200 1.254200 978102.7 978034.4 68.3 90134 128.445700 1.232300 978118.6 978034.3 84.3 90135 128.445200 1.207400 978131.9 978034.2 97.7 90136 128.432600 1.182500 978140.9 978034.1 106.8 90137 128.430300 1.154800 978161.5 978034.0 127.5 90138 128.415400 1.125700 978179.6 978033.9 145.7 90139 128.415400 1.082300 978195.3 978033.7 161.6 90140 128.413600 1.062200 978193.2 978033.6 159.6 90141 128.407000 1.039900 978183.9 978033.6 150.3 90142 128.387200 1.031000 978191.5 978033.5 158.0 90143 128.366500 1.024300 978187.2 978033.5 153.7 90144 128.344800 1.005400 978165.8 978033.5 132.3 90145 128.307500 1.581800 978146.9 978035.8 111.1 90146 128.268800 1.558200 978144.2 978035.7 108.5 90147 128.244100 1.552100 978140.0 978035.7 104.3 90148 128.219200 1.544700 978139.3 978035.6 103.7 90149 128.198700 1.543400 978140.5 978035.6 104.9 90150 128.175900 1.531200 978140.5 978035.6 104.9 90151 128.176400 1.501400 978149.8 978035.4 114.4 90152 128.195400 1.497400 978147.3 978035.4 111.9 90153 128.198300 1.474000 978158.4 978035.3 123.1 90154 128.179300 1.487900 978148.9 978035.4 113.5 90155 128.164300 1.493300 978147.9 978035.4 112.5 90156 128.154800 1.470300 978143.2 978035.3 107.9 90157 128.409900 1.316000 978160.1 978034.6 125.5 90158 128.398800 1.316000 978152.8 978034.6 118.2 90159 128.382500 1.343300 978167.0 978034.7 132.3 90160 128.308200 1.354600 978159.9 978034.8 125.1 90161 128.279800 1.358800 978156.8 978034.8 122.0 90162 128.256600 1.376000 978156.2 978034.9 121.3 90163 128.174400 1.459500 978147.8 978035.2 112.6 90164 128.120800 0.454800 978149.3 978032.2 117.1 90165 128.116000 0.479800 978145.3 978032.2 113.1 90166 128.099100 0.487900 978148.3 978032.2 116.1 90167 128.143900 0.139000 978151.8 978031.9 119.9 90168 128.174400 -0.416500 978162.1 978032.1 130.0 90169 128.204300 -0.388800 978160.3 978032.1 128.2

233 C.4 SORONG FAULT ZONE PROJECT : Gravity Expedition 1992 Survey Areas: Mayu Island, Talaud Islands and Banggai-Sula Group Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) gg^/mGal) g„(mGal) A4(mGal)

MYUOOl 126.29000 1.300000 1.5 978122.6 978034.5 88.4 MYU002 126.40000 1.330000 2.5 978113.1 978034.7 78.9 MYU003 126.38000 1.340000 5.0 978139.0 978034.7 105.3 MYU004 126.35000 1.340000 0.5 978119.8 978034.7 85.2 MYU005 126.34000 1.310000 0.5 978147.1 978034.6 112.6 MYU006 126.36000 1.300000 0.5 978129.4 978034.5 95.0 MYU007 126.38000 1.270000 1.0 978111.9 978034.4 77.7 TALOOl 126.72933 3.900330 0.0 978221.0 978056.0 165.0 TAL002 126.70133 3.940500 0.5 978233.0 978056.5 176.6 TAL003 126.66583 3.961170 0.0 978238.1 978056.8 181.3 TAL004 126.64533 3.994330 0.0 978238.6 978057.2 181.4 TAL005 126.64350 4.023670 0.0 978253.8 978057.6 196.2 TAL006 126.62217 4.041830 0.5 978226.8 978033.5 193.4 TAL007 126.61400 4.012170 0.5 978225.2 978057.4 167.9 TAL008 126.62133 3.985830 1.5 978223.2 978057.1 166.4 TAL009 126.63833 3.954000 1.0 978225.5 978056.7 169.0 TALOlO 126.65717 3.937670 1.0 978229.8 978056.5 173.5 TALOll 126.67133 3.910670 0.5 978226.7 978056.2 170.6 TAL012 126.66783 3.875670 0.5 978211.0 978055.7 155.4 TAL013 126.70467 3.870330 0.5 978224.6 978055.7 169.0 TAL014 126.70267 3.836170 0.5 978223.4 978055.2 168.3 TAL015 126.71233 3.807000 0.5 978226.2 978054.9 171.4 TAL016 126.68567 3.822670 0.0 978213.7 978055.1 158.6 TAL017 126.77317 3.847630 0.5 978241.6 978055.4 186.3 TAL018 126.80517 3.830830 0.5 978252.8 978055.2 197.7 TAL019 126.81717 3.814670 0.0 978257.3 978055.0 202.3 TAL020 126.83033 3.801330 1.5 978253.3 978054.8 198.8 TAL021 126.84183 3.772830 1.0 978242.5 978054.5 188.2 TAL022 126.83750 3.740330 2.0 978245.1 978054.1 191.4 TAL023 126.79883 3.740330 0.5 978284.7 978054.1 230.7 TAL024 126.78367 3.751270 0.5 978291.8 978054.2 237.7 TAL025 126.77217 3.761830 1.5 978297.4 978054.3 243.3 TAL026 126.75767 3.785500 0.0 978272.7 978054.6 218.1 TAL027 126.74950 3.807000 0.0 978259.9 978054.9 205.0 TAL028 126.74267 3.842330 0.0 978238.8 978055.3 183.5 TAL029 126.67367 4.006830 0.5 978240.0 978057.4 182.7 TAL030 126.71833 4.002330 0.0 978236.8 978057.3 179.5 TAL031 126.76583 3.998830 0.0 978229.9 978057.3 172.6 TAL032 126.80183 4.033170 -0.5 978217.8 978057.7 160.0 TAL033 126.80317 4.067830 1.0 978248.4 978058.2 190.4 TAL034 126.80600 4.110330 1.0 978251.7 978058.7 193.2

234 SORONG FAULT ZONE PROJECT Gravity Expedition 1992 Survey Areas; Mayu Island, Talaud Islands and Banggai-Sula Group Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) g^^^/mGal) ^„(mGal) Æ4(mGal)

TAL035 126.79417 4.154670 0.5 978234.5 978059.3 175.3 TAL036 126.83133 4.189830 0.0 978214.9 978059.7 155.2 TAL037 126.85933 4.233670 0.0 978201.3 978060.3 141.0 TAL038 126.85983 4.250170 0.0 978210.8 978060.6 150.2 TAL039 126.78933 4.23183Ô 1.0 978231.7 978060.3 171.6 TAL040 126.75683 4.174170 0.5 978253.0 978059.5 193.6 TAL041 126.74967 4.146500 0.5 978263.4 978059.2 204.3 TAL042 126.73750 4.127170 0.5 978272.6 978058.9 213.8 TAL043 126.73117 4.108330 0.5 978271.7 978058.7 213.1 TAL044 126.71500 4.087500 1.0 978270.1 978058.4 211.9 TAL045 126.68983 4.077000 1.5 978267.0 978058.3 209.0 TAL046 126.67417 4.051500 0.0 978251.6 978057.9 193.7 TAL047 126.66667 4.027170 0.0 978242.9 978057.6 185.3 TAL048 126.75433 4.167330 1.0 978258.2 978059.5 198.9 TAL049 126.77483 4.201670 0.5 978248.0 978059.9 188.2 TAL050 126.88633 4.259170 0.0 978203.8 978060.7 143.1 TAL051 126.89683 4.309830 0.0 978185.9 978061.4 124.5 TAL052 126.85367 4.371670 1.0 978199.7 978062.2 137.7 TAL053 126.85367 4.404330 0.0 978201.9 978062.7 139.2 TAL054 126.86800 4.444830 0.0 978190.5 978063.2 127.3 TAL055 126.85767 4.477000 0.0 978172.3 978063.7 108.6 TAL056 126.83167 4.496170 0.0 978161.9 978064.0 97.9 TAL057 126.81850 4.522830 0.0 978156.2 978064.3 91.9 TAL058 126.77833 4.523170 0.0 978149.2 978064.4 84.8 TAL059 126.75667 4.543830 0.0 978151.3 978064.7 86.6 TAL060 126.72467 4.507000 0.0 978144.7 978064.1 80.6 TAL061 126.73283 4.486330 0.0 978147.7 978063.8 83.9 TAL062 126.73417 4.474830 0.0 978152.8 978063.7 89.1 TAL063 126.73133 4.456170 0.0 978166.4 978063.4 103.0 TAL064 126.72100 4.436830 0.0 978178.1 978063.1 115.0 TAL065 126.72117 4.407000 0.0 978181.9 978062.7 119.2 TAL066 126.69583 4.374830 0.0 978186.9 978062.3 124.6 TAL067 126.68883 4.356000 0.0 978190.3 978062.0 128.3 TAL068 126.69800 4.330830 0.0 978194.6 978061.7 132.9 TAL069 126.71367 4.307000 2.0 978204.6 978061.3 143.7 TAL070 126.71600 4.273330 0.5 978217.0 978060.9 156.2 TAL071 126.76483 4.251330 0.5 978223.1 978060.6 162.6 TAL072 126.80850 4.252330 2.0 978234.3 978060.6 174.1 BGIOOl 123.49883 -1.589670 1.5 978135.9 978035.9 100.3 BGI002 123.49400 -1.532330 0.0 978130.8 978035.6 95.2 BGI003 123.48983 -1.467170 0.0 978127.3 978035.3 92.0

235 SORONG FAULT ZONE PROJECT Gravity Expedition 1992 Survey Areas; Mayu Island, Talaud Islands and Banggai-Sula Group Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) ^o6^(mGal) ^„(mGal) A4(mGal)

BGI004 123.52350 -1.424670 0.5 978122.4 978035.1 87.4 BGI005 123.53383 -1.365830 1.5 978116.3 978034.8 81.8 BGI006 123.55350 -1.294330 1.5 978099.7 978034.5 65.5 BGI007 123.48717 -1.268500 1.0 978092.6 978034.4 58.4 BGI008 123.40883 -1.256330 2.0 978104.8 978034.4 70.8 BGI009 123.35117 -1.242830 1.0 978100.9 978034.3 66.8 BGIOlO 123.30383 -1.283670 0.0 978113.0 978034.5 78.5 BGIOll 123.28367 -1.341830 0.5 978128.6 978034.7 94.0 BGI012 123.25250 -1.391830 0.5 978126.8 978034.9 92.0 BGI013 123.21767 -1.342170 0.5 978123.3 978034.7 88.7 BGI014 123.21117 -1.273330 0.5 978112.2 978034.4 77.9 BGI015 123.24617 -1.232670 1.0 978102.6 978034.3 68.5 BGI016 123.27867 -1.177000 1.0 978078.2 978034.1 44.3 BGI017 123.16333 -1.157170 1.0 978080.6 978034.0 46.8 BGI018 123.14717 -1.210830 0.5 978094.0 978034.2 59.9 BGI019 123.10450 -1.165170 0.5 978083.4 978034.0 49.5 BGI020 123.04400 -1.179330 0.0 978085.7 978034.1 51.6 BGI021 122.98583 -1.202500 1.0 978087.4 978034.2 53.4 BGI022 122.92433 -1.187500 2.0 978077.4 978034.1 43.7 BGI023 122.88283 -1.215330 0.5 978085.2 978034.2 51.1 BGI024 122.85283 -1.263330 0.5 978092.1 978034.4 57.8 BGI025 122.82333 -1.301170 0.5 978095.6 978034.5 61.2 BGI026 122.75117 -1.332670 0.5 978087.0 978034.7 52.4 BGI027 122.80667 -1.357670 0.0 978099.7 978034.8 64.9 BGI028 122.79633 -1.405000 0.5 978097.7 978035.0 62.8 BGI029 122.78883 -1.463170 0.5 978100.0 978035.3 64.8 BGI030 122.74233 -1.496330 0.0 978085.5 978035.4 50.1 BGI031 122.83000 -1.511500 1.0 978103.3 978035.5 68.0 BGI032 122.86050 -1.564330 1.0 978106.8 978035.7 71.3 BGI033 122.89717 -1.609330 2.0 978117.2 978036.0 81.6 BGI034 122.93650 -1.576500 0.0 978119.1 978035.8 83.3 BGI035 122.98083 -1.542220 0.5 978121.4 978035.6 85.9 BGI036 123.03767 -1.452670 0.0 978119.4 978035.2 84.2 BGI037 123.07717 -1.395500 0.0 978119.7 978034.9 84.8 BGI038 123.10550 -1.347830 2.0 978117.5 978034.7 83.2 BGI039 123.16033 -1.313000 0.0 978114.1 978034.6 79.5 BGI040 123.15800 -1.369830 0.0 978118.6 978034.8 83.8 BGI041 123.16883 -1.424330 1.0 978128.9 978035.1 94.0 BGI042 123.18217 -1.481000 1.0 978132.5 978035.3 97.4 BGI043 123.17700 -1.533670 0.5 978131.7 978035.6 96.2 BGI044 123.11583 -1.564330 0.0 978132.0 978035.7 96.3

236 SORONG FAULT ZONE PROJECT Gravity Expedition 1992 Survey Areas: Mayu Island, Talaud Islands and Banggai-Sula Group Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) ^ofo(mGal) g«(mGal) &4(mGal)

BGI045 123.10817 -1.606170 0.0 978131.3 978036.0 95.3 BGI046 123.16017 -1.652170 0.0 978143.8 978036.2 107.6 BGI047 123.12683 -1.731330 0.0 978131.3 978036.6 94.7 BGI048 123.09117 -1.774170 0.5 978130.1 978036.9 93.3 BGI049 123.06500 -1.829500 2.0 978129.2 978037.2 92.4 BGI050 123.06350 -1.868670 2.0 978128.4 978037.4 91.4 BGI051 123.06867 -1.921670 0.5 978129.8 978037.7 92.2 BGI052 123.10833 -1.880330 0.0 978131.5 978037.5 94.0 BGI053 123.14783 -1.853670 0.0 978131.6 978037.3 94.3 BGI054 123.14567 -1.799830 0.5 978135.8 978037.0 98.9 BGI055 123.31367 -1.718170 0.5 978132.3 978036.5 95.8 BGI056 123.26717 -1.793170 1.5 978140.4 978037.0 103.7 BGI057 123.32417 -1.764500 1.0 978133.3 978036.8 96.7 BGI058 123.36833 -1.725170 1.0 978134.6 978036.6 98.2 BGI059 123.38367 -1.674670 0.5 978136.2 978036.3 100.0 BGI060 123.25317 -1.641330 -1.0 978134.7 978036.1 98.4 BGI061 123.24717 -1.573830 0.5 978128.1 978035.8 92.4 BGI062 123.25117 -1.507000 2.0 978129.1 978035.5 94.0 BGI063 123.29200 -1.425830 0.5 978133.9 978035.1 98.9 BGI064 123.31367 -1.414500 0.5 978133.2 978035.0 98.3 BGI065 123.33933 -1.460170 1.5 978136.5 978035.2 101.6 BGI066 123.35900 -1.524330 0.5 978138.4 978035.5 102.9 BGI067 123.42000 -1.520830 1.0 978136.9 978035.5 101.6 BGI068 123.48483 -1.633500 0.0 978134.9 978036.1 98.8 BGI069 123.47850 -1.681670 0.0 978131.1 978036.4 94.7 BGI070 123.52983 -1.713170 0.0 978132.9 978036.5 96.4 BGI071 123.57767 -1.723170 0.0 978132.9 978036.6 96.3 BGI072 123.52533 -1.760500 0.0 978138.7 978036.8 101.9 BGI073 123.58150 -1.606670 3.0 978124.5 978036.0 89.1 BGI074 123.55817 -1.556670 0.5 978129.3 978035.7 93.7 BGI075 123.51817 -1.512170 1.5 978127.8 978035.5 92.6 SULOOl 124.38000 -1.830000 0.5 978202.0 978037.2 164.9 SUL002 124.39000 -1.890000 0.0 978217.2 978037.5 179.7 SUL003 124.48000 -1.880000 0.5 978225.9 978037.5 188.5 SUL004 124.56000 -1.870000 4.0 978228.3 978037.4 191.7 SUL005 124.64000 -1.860000 2.0 978238.4 978037.4 201.4 SUL006 124.66000 -1.850000 2.0 978241.1 978037.3 204.2 SUL007 124.69000 -1.840000 1.0 978248.5 978037.2 211.5 SUL008 124.76000 -1.810000 0.5 978240.1 978037.1 203.1 SUL009 124.84000 -1.790000 2.0 978253.7 978036.9 217.1 SULOlO 124.91000 -1.820000 0.5 978266.2 978037.1 229.2

237 SORONG FAULT ZONE PROJECT Gravity Expedition 1992 Survey Areas: Mayu Island, Talaud Islands and Banggai-Sula Group Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) g^^mGal) grn(mGal) &4(mGal)

SULOll 125.00000 -1.830000 0.0 978278.7 978037.2 241.5 SUL012 125.04000 -1.790000 0.5 978294.3 978036.9 257.4 SUL013 125.12000 -1.780000 0.5 978296.6 978036.9 259.8 SUL014 125.19000 -1.780000 1.0 978300.3 978036.9 263.6 SUL015 125.29000 -1.790000 -0.5 978305.5 978036.9 268.5 SUL016 125.41000 -1.830000 0.5 978338.9 978037.2 301.8 SUL017 125.50000 -1.820000 0.5 978352.9 978037.1 315.9 SUL018 125.40000 -1.770000 0.5 978309.1 978036.8 272.4 SUL019 125.35000 -1.780000 0.0 978310.4 978036.9 273.5 SUL020 124.33000 -1.790000 0.5 978196.0 978036.9 159.1 SUL021 124.33000 -1.740000 0.5 978189.5 978036.7 152.9

238 C.5 SORONG FAULT ZONE PROJECT : Gravity Expedition 1993 Survey Areas: East Coast Central Sulawesi Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) ^oij(mGal) ^„(mGal) A4(mGal)

93001 121.34467 -2.005670 1.2 978042.8 978038.3 4.8 93002 121.34800 -1.966170 0.3 978047.5 978038.0 9.6 93003 121.32933 -1.932500 0.8 978049.9 978037.8 12.3 93004 121.34567 -1.898670 0.3 978055.0 978037.6 17.5 93005 121.38733 -1.864830 0.8 978081.5 978037.4 44.3 93006 121.34800 -1.948170 0.3 978068.9 978037.9 31.1 93007 121.30417 -1.853670 0.1 978058.5 978037.3 21.2 93008 121.29733 -1.806330 0.2 978052.9 978037.0 15.9 93009 121.33783 -1.772500 0.5 978073.9 978036.9 37.1 93010 121.37167 -1.808500 0.6 978076.9 978037.1 40.0 93011 121.41667 -1.819830 0.3 978068.3 978037.1 31.2 93012 121.44600 -1.837830 0.3 978071.2 978037.2 34.0 93013 121.52250 -1.898670 -0.5 978060.8 978033.5 27.2 93014 121.57483 -1.952670 0.5 978045.5 978037.9 7.7 93015 121.50783 -1.948330 0.5 978053.7 978037.9 15.9 93016 121.53600 -2.049500 0.6 978036.3 978038.5 -2.1 93017 121.53633 -2.103670 0.8 978036.7 978038.9 -2.0 93018 121.53933 -2.042830 0.8 978045.2 978038.5 6.9 93019 121.50450 -2.042830 -0.5 978040.4 978038.5 1.8 93020 121.42800 -1.997830 0.8 978050.4 978038.2 12.4 93021 121.45500 -1.925670 0.5 978045.2 978037.8 7.5 93022 121.47400 -1.914500 0.8 978055.8 978037.7 18.3 93023 121.44367 -1.914500 0.5 978059.3 978037.7 21.7 93024 121.39533 -1.907670 0.5 978056.9 978037.6 19.4 93025 121.37167 -1.934670 0.5 978050.8 978037.8 13.1 93026 121.37167 -1.978670 0.5 978044.5 978038.1 6.5 93027 121.54950 -2.163170 0.8 978038.9 978039.3 -0.2 93028 121.60250 -2.208670 0.3 978048.1 978039.6 8.5 93029 121.74883 -2.212830 0.6 978044.2 978039.6 4.7 93030 121.76350 -2.259000 0.5 978044.4 978040.0 4.5 93031 121.80733 -2.297330 0.5 978039.7 978040.2 -0.4 93032 121.84117 -2.354670 0.5 978039.3 978040.7 -1.3 93033 121.88283 -2.419000 0.5 978048.2 978041.2 7.1 93034 121.92567 -2.475670 0.5 978056.3 978041.6 14.8 93035 121.96617 -2.544170 0.3 978065.7 978042.1 23.6 93036 121.99550 -2.613170 0.5 978076.0 978042.7 33.4 93037 122.00950 -2.673500 0.8 978073.2 978043.2 30.1 93038 122.06300 -2.760170 0.5 978079.1 978044.0 35.2

239 SORONG FAULT ZONE PROJECT Gravity Expedition 1993 Survey Areas: East Coast Central Sulawesi Longitude and Latitude are expressed in decimal degrees

Station Longitude (East) Latitude Elevation(m) goAf(mGal) grn(mGal) A4(mGal)

93039 122.13450 -2.788830 -0.5 978072.0 978044.2 27.7 93040 122.18000 -2.862500 1.0 978098.9 978044.9 54.2 93041 122.19350 -2.878330 2.0 978100.4 978045.0 55.8 93042 122.18567 -2.828830 0.5 978094.6 978044.6 50.1 93043 122.08667 -2.786000 0.5 978080.0 978044.2 35.9 93044 122.01800 -2.723000 0.8 978059.2 978043.6 15.7 93045 121.86817 -2.401000 0.3 978041.2 978041.0 0.2 93046 121.67900 -2.173500 0.8 978050.3 978039.4 11.1 93047 121.64300 -2.187500 -0.5 978046.8 978039.5 7.2

240 Appendix D

Table D.l List of principal base stations of the Indonesian Regional Gravity Network and sketches of base stations established during the gravity expeditions of the Sorong Fault Zone Project

No. Nearest Town Base Station Name Station Number Longitude Latitude Elevation (m) Gravity (mGal)

1 Banda Aceh Blang Bintang 7693.0161 95°25.0’E 5°31.0’N 19.2 978114.99 2 Medan Polonia 1 7693.0160 98°41.0’E 3°34.0’N 27.1 978035.05 3 Pakanbaru Pakanbaru 7693.0159 101°27.0’E 0°28.0’N 31.1 978039.20 4 Padang Tabing 7693.0158 100°21.0’E 0°53.0’N 6.1 978034.68 5 Singapore Paya Lebar 7693.0162 103°55.0’E 1°22.0’N 18.0 978065.43 6 Palembang Palembang 7693.0157 104°42.0’E 2°54.0’S 10.1 978092.36 7 Telukbetimg Branti 7793.0176 105°11.0’E 5°15.0’S 61.1 978115.18 8 Jakarta Halim ‘Old’ 7693.0253 106°53.7’E 6°16.0’S 25.6 978142.34 9 Bandung Husein Sastra Negara 7693.0852 107°35.0’E 6°54.0’S 742.3 977979.72 10 Semarang Achmad Yard 7793.0177 110°23.0’E 6°59.0’S 3.1 978117.32 11 Yogyakarta Adisucipto 7693.0156 110°26.0’E 7°47.0’S 107.6 978196.34 12 Surabaya Juanda 7693.0154 112°46.0’E 7°22.0’S 3.1 978088.24 13 Pontianak Supadio 7793.0175 109°24.0’E 0°09.0’S 3.1 978068.96 14 Palangka Raya Panarung 7793.0174 113°57.0’E 2°16.0’S 25.0 978058.10 15 Banjarmasin Syamsudin Noor 7693.0169 114°45.0’E 3°28.0’S 21.0 978048.82 16 Balikpapan Sepinggan 7793.0170 116°54.0’E r i6 .0 ’S 3.1 978038.95 17 Samarinda Temindung 7793.0171 117°09.0’E 0°27.0’S 9.2 978055.37 18 Tarakan Tarakan 7793.0173 117°34.0’E 3°20.0’N 6.1 978083.02 19 Denpasar NgurahRai 7693.0155 115°06.0’E 8°43.5’S 3.0 978269.85 20 Ampenan Selaparang 7693.0172 116°04.5’E 8°32.0’S 15.0 978288.42 21 Bima Palibelo 7793.0183 118°42.0’E 8°35.0’S 2.1 978251.69 22 Tambolaka Waikabubak 7793.0179 119°24.0’E 9°24.0’S 48.4 978287.54 23 Waingapu Mau-Hau 7793.0180 120°18.0’E 9°40.0’S 12.2 978295.13 24 Ende Ende 7793.0182 121°36.0’E 8°48.0’S 3.0 978260.66 25 Kupang Penfui 7793.0181 123°40.0’E 10°10.0’S 102.3 978157.03 No. Nearest Town Base Station Name Station Number Longitude Latitude Elevation (m) Gravity (mGal)

26 Ujung Pandang Hasanuddin 1 7693.0163 119°33.0’E 5*04.0’S 32.0 978119.94 27 Manado Sam Ratulangi ‘New’ 7793.0364 124°55.0’E 1*32.0’N 81.2 978186.30 28 Ambon Pattimura 7693.0168 128*05.0’E 3*42.0’S 10.1 978164.80 29 Sorong Jefinan Island 7693.0165 131°07.0’E 0*56.0’S 3.1 978116.26 30 Biak Mokmer 7693.0166 136*07.1’E 1*12.0’S 14.0 978108.30 31 Jayapura Jayapura Post Office 7693.0267 140*42.0’E 2*40.0’S 80.0 978170.10 32 Sydney Kingsford Smith 7693.0147 151*10.0’E 33*56.2’S 4.0 979682.81

No. International Absolute Gravity Station Station Number Longitude Latitude Elevation (m) Gravity (mGal)

1 Malaya University ‘A ’ Singapore 7693.0262 103*49.1'E in9.1’N 19.2 978066.66 2 Sydney University ‘A’ Sydney 7693.0247 151*11.4’E 33°53.4'S 29.6 979671.86 NEAREST CITY Lirung COUNTRY INDONESIA GRAVITY STATION DESCRIPTION

STATE N NAM E TALAUD ; T.02 ST A T IO N N O . 9201.0001STATIO PROVINCE MOLUCCA COUNTY LATITUDE 3” 56.4' N LONGITUDE 126° 42.1' E ELEVATION 0.5 m

POSITION CONTROL GRAVITY VALUE 978232.9 mCal VISUAL AND TOPOGRAPHIC MAP

ELEVATION CONTROL BOUGUER ANOMALY 176.7 mGal DIRECT REFERENCE TO SEA LEVEL

DESCRIPTION

The station is situated opposite to the Camat Office, on the concrete stairs, three steps from the bottom.

DESCRIBED BY: Sardjono DATE 12-Oct-92

DIAGRAM

GENERAL DETAIL

Sea Sea

C oncrvte )et(y Concrete Stairs

Lirung H a rlx ju r Concrete Stairs

Pom CHfice

Camat Office to Post Office

Main Road

D IA G R A M BY: Sardjono DATE 29-Apr-93

STATION HISTORY

When the gravimeter reading was taken, the Lirung Hartxfur was under construction and expansion.

SOURCE ORGANISATION The Geological Research and Development Centre, Indonesia and The University of London, Consortium for Geological Research in Southeast Asia

Figure D.l Sketch of gravity base station Lirung Harbour, Talaud Islands

243 INDONESIACOUNTRY NEAREST CITY L uw uk GRAVITY STATION DESCRIPTION

STATE CENTRAL STATION NAME STATION NO. 9301.0001 PROVINCE Hotel Melati SULAWESI COUNTY LATITUDE LONGITUDE 122° 47.43 E ELEVATION 2 .5 m

POSITION CONTROL GRAVITY VALUE 978040.35 mGal VISUAL AND TOPOGRAPHIC MAP

ELEVATION CONTROL BOUGUER ANOMALY 7 .1 5 m G al DIRECT REFERENCE TO SEA LEVEL

DESCRIPTION

The station is situated on the terrace in front of the hotel, near the telephone box.

DESCRIBED BY: Sardjono DATE 3 June 93

DIAGRAM

GENERAL DETAIL

Hotel Melatl

p h o n e b o x

main entrance

DIA G R A M BY: Sardjono DATE 25 October 93

STATION HISTORY

The station was first established in June 1993, during the course of the coastal gravity survey of the east coast Central Sulawesi.

SOURCE ORGANISATION The Geological Research and Development Centre. Indonesia and The University of London. Consortium for Geological Research in Southeast Asia

Figure D.2 Sketch of gravity base station Luwuk Hotel Melati, Central Sulawesi

244 COUNTRY INDONESIA NEAREST CITY L uw uk GRAVITY STATION DESCRIPTION

STATE STATION NO. 9301,0002 CENTRAL STATION NAME PROVINCE Bubung Airport SULAWESI COUNTY LATITUDE LONGITUDE 122M4.73E ELEVATION

POSITION CONTROL GRAVITY VALUE 978050.46 mGal VISUAL AND TOPOGRAPHIC MAP

ELEVATION CONTROL BOUGUER ANOMALY

DESCRIPTION

The station is situated in the com er of the terminal building, to the right of the arrival hall, in the public area.

DESCRIBED BY: Sardjono DATE 3 June 93

DIAGRAM

GENERAL DETAIL

DIAGRAM BY: S a rd jon o DATE 25 October 93

STATION HISTORY

The station was first established in June 1993, during the course of the coastal gravity survey of the east coast Central Sulawesi.

SOURCE ORGANISATION The Geological Research and Development Centre, Indonesia and The University of London, Consortium for Geological Research in Southeast Asia

Figure D.3 Sketch of gravity base station Luwuk Bubung Airport, Central Sulawesi

245 COUNTRY INDONESIA NEAREST CITY Banggai GRAVITY STATION DESCRIPTION

STATE STATION NAME BANGGAI; BGO STATION NO. 9201.0002 PROVINCE CENTRAL COUNTY SULAWESI LATITUDE 1°35.4' LONGITUDE 123° 29.3' ELEVATION 1.5 m

POSITION CONTROL GRAVITY VALUE 978135.54 mGal VISUAL AND TOPOGRAPHIC MAP

ELEVATION CONTROL BOUGUER ANOMALY 99.76 mGal DIRECT REFERENCE TO SEA LEVEL

DESCRIPTION

The station is at the comer of the copra-drying yard behind the copra storage, adjacent to the karaoke bar. Access is through an entrance path beside the copra storage opposite the TELKOM office.

DESCRIBED BY: Sardjono DATE 5 -N O V -9 2

DIAGRAM

GENERAL DETAIL

Karaoke Bar Shop (facing «0 sea)

BGO®

b o r a g e

Concrete Stairs ,

Concrete Barrier

D IA G R A M BY: Sardjono DATE l-May-93

STATION HISTORY

BGO gravity base station was first established when the gravity surveys of Banggai-Sula region was carried out (Nov 1992). The backup station BGl at Los men Padang Laya was established but its elevation was not determined.

Previous gravity value obtained from the 1992 survey was 978137.54 mGal. This value was updated with the result obtained from the Luwuk-Banggai Gravity Tie 1993.

SOURCE ORGANISATION The Geological Research and Development Centre, Indonesia and The University of London, Consortium for Geological Research in Southeast Asia

Figure D.4 Sketch of gravity base station Banggai, Banggai Islanii, Central Sulawesi

246 COUNTRY INDONESIA NEAREST CITY K olonodale GRAVITY STATION DESCRIPTION

STATE CENTRAL STATION NAME STATION NO. 9301.0003 PROVINCE Hotel Lestari SULAWESI COUNTY

LATITUDE 2°0.34'S LONGITUDE 121° 20.68' ELEVATION 1 . 2 m

POSITION CONTROL GRAVITY VALUE 978042.56 mGal VISUAL AND TOPOGRAPHIC MAP

ELEVATION CONTROL BOUGUER ANOMALY 4 4 4 m G al DIRECT REFERENCE TO SEA LEVEL

DESCRIPTION

The station is situated in the backw ard of the hotel, on the concrete pad near a wooden hut.

DESCRIBED BY; Sardjono DATE 10 June 93

DIAGRAM

GENERAL DETAIL

Jotel Hotel Lestari .oloi

D IA G R A M BY: Sardjono DATE 25 October 93

STATION HISTORY

The station was first established in June 1993, during the course of the coastal gravity survey of the east coast Central Sulawesi.

SOURCE ORGANISATION The Geological Research and Development Centre. Indonesia and The University of London. Consortium for Geological Research in Southeast Asia

Figure D.5 Sketch of gravity base station Kolonodale Hotel Lestari, Central Sulawesi

247 Appendix E Barometric Levelling

Dry air is assumed to behave as a perfect gas, i.e. ( 1) p = pr 0, where p is the pressure at a point in a gas, p and 0 the corresponding density and temperature and r the appropriate gas constant.

In a column of air at equilibrium, the weight of the gas is supported by the pressure difference, i.e. (2) dpidh = -pg and substituting for p from ( 1) to obtain (3) dpip = -g dhir 0 and integration of both sides of (3) gives the relationship between pressure and height. For an isothermal atmosphere 0 is constant.

p. ^ ^ _g_ f‘. dh ho p r 0 K

(4) log ( 1 + h , where h = ^ with Ap = p, -

For an atmosphere with a uniform lapse rate Q = Qq - sh where s is the lapse rate.

fPi È.dp _ = - g 1 r\r dh p r KKp (0Q - sh)

(5) ( 1 + ) * = 1 - — setting h^ = 0 Po

Equation (4) may be expanded using the log series and (5) using the binomial expansion (Ap being always less than p^). Setting Ap/p^ = x, for the isothermal case

(6) -_É _ = f f + ... r % 2 3 4 and with a uniform lapse rate we may write

l-flL = 00 8 '^8 g ^8 8 8 24g g g g in both cases ignoring terms higher than x. Since Ap/p will seldom exceed 0.2, the factor rs/g will have a value of approximately 0.2, thus mixed terms of the fourth power may also be ignored. The lapse rate equation becomes

248 (7) ^ = x - — x^ + — x^- — + —— ( x^ - x^ ) r 8 o 2 3 4 2 g

In both cases the expression 0^ is assumed to be the temperature measured at ground level. The ground temperature can be used to obtain a mean air column temperature,

0g - V2sh, and substituting this in the Isothermal formula to give

-gh = r{Q- — sh)(x- — x^ + — x^- — x"^) ° 2 2 3 4 or

where

I = x- ~ x^ + — x^-—X substituting again for h on the right hand side gives

- i h . = Q.I * 1 rs (e.I - I sh I ) L r “ 2 " 2 g the term ^Ars, Vish and P will involve, as the term of lowest power

rs .2 / A/7 ^3 ( _ ^ ) S Po and may therefore be neglected i.e. -A A = e, / + Iff. 0 p r “ 2 g " and again ignoring terms higher than the fourth power gives

-1 h ^ % I * 1— 9„ ( - x’ ) which is identical with the lapse rate formula. Hence, if the true mean temperature of the air column is used, the isothermal formula is no less accurate than the uniform lapse rate formula.

249 Appendix F

Information on density of rocks Sorong Fault Zone and Kai Islands Region

Table F.l. Density values obtained from velocity of compressional wave (Analysed from seismic images discussed in Section 5.2 of this thesis) Interval Panel TWT Velocity. time depth Velocity Density Numbers (m sec) ( m.s** ) (msec) (km) ( km.s’‘ ) (Mg.m-")

1 0.1 1440 135 0.10 1.44 1.03 190 1440 352 0.34 1.91 1.92 280 1714 450 0.45 2.00 1.93 350 2000 830 0.97 2.33 2.06 840 2400 2010 3.64 3.63 2.34 1520 2769 6000 11.18 5.73 2.66 2010 4000 6000 6000

2 0.1 1440 145 0.10 1.44 1.03 190 1440 315 0.27 1.70 1.79 300 1714 650 0.64 1.97 1.93 650 2000 1060 1.17 2.20 2.02 840 2117 1080 2250 1.19 2.21 2.03 1440 2571 1.80 2.50 2.12 1970 3000 2.84 2.89 2.20 3150 3600 5.45 3.46 2.32 6000 4250 11.72 3.91 2.38

3 0.1 1440 190 0.14 1.44 1.03 240 1440 500 0.42 1.69 1.78 390 1565 530 0.46 1.73 1.81 560 1800 1180 1.23 2.08 1.96 1080 2117 1440 1.50 2.09 1.97 1470 2117 1510 1.61 2.11 1.99 2270 2571 2.83 2.50 2.12 3840 3272 6.03 3.14 2.25 6000 3800 10.99 3.66 2.34

4 0 1440 140 0.10 1.44 1.03 180 1440 435 0.38 1.74 1.82 380 1714 1120 1.23 2.19 2.00 740 2000 1535 1.83 2.40 2.08 1400 2400 1840 2571 2.32 2.52 2.12 6000 3272 9.68 3.23 2.27

250 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) (m.s‘^) ( msec ) (km) ( km.s ^ ) (Mg.m-^>

5 1 1470 750 0.55 1.47 1.04 760 1470 1150 0.96 1.66 1.77 930 1500 1900 1.83 1.93 1.91 1030 1565 2275 2.25 1.98 1.92 1160 1714 1380 1800 1970 2000 2700 2058 2.73 2.02 1.94 3520 2117 3.67 2.09 1.97 4100 2183 4.41 2.15 1.99 6000 2400 7.08 2.36 2.06

6 0.1 1440 1825 1.32 1.45 1.03 1800 1440 2270 1.83 1.61 1.74 2010 1500 2360 1.93 1.64 1.76 2120 1565 2530 2.14 1.69 1.79 2220 1636 2870 2.63 1.83 1.86 2690 1800 3200 3.19 1.99 1.93 3180 2117 3670 3.75 2.04 1.95 4740 2250 5.11 2.16 1.99 5700 2400 6.57 2.31 2.05 6560 2571 8.17 2.46 2.09 7000 2769 9.14 2.61 2.14

7 0.1 1440 2220 1.58 1.44 1.03 2210 1440 2790 2.37 1.70 1.79 2410 1636 3340 3.22 1.93 1.91 2670 1714 3670 3.66 2.00 1.93 2980 1894 3350 2058 3670 2117 4110 2400 4.55 2.22 2.02 4880 2571 5.84 2.39 2.09 5900 2769 7.66 2.60 2.14 7000 3000 9.87 2.82 2.20

8 0.1 1440 1900 1.37 1.44 1.03 1910 1440 2390 1.92 1.60 1.73 2120 1500 2350 1636 2850 1714 2.39 1.68 1.77 3500 1894 3.21 1.84 1.86 4120 2000 3.99 1.94 1.91 4750 2400 5.30 2.23 2.02 5200 2485 6.03 2.23 2.06 7000 2769 9.14 2.61 2.13

251 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) ( m.s^ ) ( msec ) (km) ( km.s'* ) (Mg.m^)

9 0.1 1500 2360 1.77 1.50 1.03 2340 1500 2545 1.94 1.52 1.62 2500 1500 3850 3.78 1.96 1.67 2700 1636 2.16 1.60 1.73 2930 1800 2.52 1.72 1.81 3130 1894 2.81 1.80 1.84 3360 2000 3.17 1.89 1.88 5050 2250 5.43 2.15 1.99 7380 2571 9.11 2.47 2.10 8000 2769 10.50 2.63 2.14

10 0.1 1440 2180 1.57 1.44 1.03 2220 1440 2375 1.74 1.46 1.46 2390 1470 2550 1.91 1.50 1.58 2500 1500 2900 1565 2.25 1.55 1.66 3680 1636 2.98 1.62 1.76 4050 1800 3.53 1.74 1.82 4770 2117 4.75 1.99 1.93 6000 2400 6.76 2.25 2.02 8000 2769 10.42 2.61 2.13

11 0.1 1440 2730 1.97 1.45 1.03 2670 1440 3000 2.21 1.47 3250 1500 3675 3.02 1.65 3370 1532 3480 1565 3680 1714 4040 1894 3.61 1.79 1.87 5680 2400 6.34 2.23 2.02 6640 2769 8.43 2.51 2.11 8000 3000 11.11 2.78 2.16

12 velocity panel not complete

13 0.1 1500 1810 1.36 1.50 1.03 1960 1500 2340 1.85 1.58 1.69 2160 1532 3540 3.64 2.05 1.70 2370 1600 1.88 1.59 1.71 2470 1714 2.05 1.66 1.77 2610 1894 2.32 1.78 1.82 3130 2117 3.10 1.98 1.92 3980 2250 4.24 2.13 1.99 4800 2400 5.48 2.28 2.03 5730 2571 7.02 2.45 2.09 7000 2769 9.26 2.65 2.15

252 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) (m.s'^) ( msec ) (km) ( km.s^ ) (Mg.m")

14 0.1 1470 1800 1.33 1.48 1.03 1740 1470 2090 1.57 1.50 1.59 2060 1500 2230 1536 1.71 1.53 1.64 2580 1714 2.16 1.67 1.77 2820 1894 2.55 1.81 1.85 3090 2000 2.94 1.90 1.89 3350 2117 3.35 2.00 1.94 4020 2400 4.52 2.25 2.02 7000 2769 9.29 2.65 2.15

15 0.1 1440 1740 1.26 1.45 1.03 1690 1440 2000 1.52 1.52 1.62 1950 1500 2050 1565 1.58 1.54 1.65 2150 1636 1.72 1.60 1.73 2270 1800 1.94 1.71 1.80 2520 1894 2.26 1.79 1.84 2760 2000 2.61 1.89 1.89 3230 2250 3.40 2.10 1.97 4130 2400 4.69 2.27 2.06 7000 2769 9.32 2.66 2.15

16 0.1 1440 1790 1.29 1.44 1.03 1830 1440 2050 1.49 1.46 1.42 2330 1470 1.64 1.47 1.44 2400 1500 1.79 1.50 1.59 2540 1565 1.96 1.55 1.65 2810 1714 2.33 1.66 1.77 3120 1800 2.71 1.74 1.82 3370 2000 3.17 1.88 1.87 3670 2117 3.64 1.99 1.94 7000 2769 9.21 2.63 2.14

17 0.1 1440 2060 1.48 1.44 1.03 2320 1440 2325 1.67 1.44 2540 1470 2570 1.89 1.47 2820 1500 2900 2.18 1.50 3130 1532 2.39 1.53 3250 1565 2.52 1.55 3660 1714 3.06 1.67 1.77 3800 1847 3.33 1.76 1.83 4000 2000 3.72 1.86 1.87 4420 2185 4.46 2.02 1.94 7000 2769 9.04 2.58 2.13

253 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) ( m.s'^ ) ( msec ) (km) ( km.s'* ) (Mg.m")

18 0.1 1440 2490 1.79 1.44 1.03 2650 1440 2740 1.99 1.45 2850 1470 3030 2.24 1.48 3180 1500 3460 2.67 1.55 3480 1565 2.70 1.55 3620 1565 2.81 1.55 3910 1636 3.15 1.61 4100 1714 3.42 1.67 4230 1894 3.74 1.77 5120 2000 4.83 1.89 1.88 8000 2400 9.12 2.28 2.10

19 0.1 1440 2855 2.06 1.44 1.03 2870 1440 3100 2.28 1.47 3070 1470 3300 2.45 1.49 3400 1500 3420 2.56 1.49 3590 1500 2.68 1.49 3770 1532 2.87 1.52 3940 1565 3.05 1.55 4070 1600 3.21 1.58 4360 1675 3.57 1.64 4850 1800 4.23 1.74 1.81 5540 2117 5.48 1.98 1.93 8000 2571 9.63 2.41 2.09

20 0.1 1440 3165 2.28 1.44 1.03 3180 1440 3500 2.62 1.50 3380 1500 3710 2.80 1.51 3830 1532 2.91 1.52 4120 1565 3.19 1.55 4400 1636 3.53 1.61 4950 1714 4.15 1.68 5330 1800 4.66 1.75 5720 1894 5.22 1.83 5880 2117 5.71 1.94 1.91 9000 2769 11.47 2.55 2.13

21 0.1 1440 3150 2.27 1.44 1.03 3160 1440 3400 2.50 1.47 3570 1500 3775 2.85 1.51 3930 1532 2.99 1.52 4100 1565 3.18 1.55 4690 1636 3.79 1.61 5190 1800 4.52 1.74 5370 1847 4.78 1.78 1.84 5680 2058 5.44 1.92 1.91 8000 2571 9.53 2.38 2.08

254 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) ( m.s‘* ) ( msec) (km) (km.s‘‘) (Mg.m-^)

22 0.1 1440 3030 2.18 1.44 1.03 3040 1440 3300 2.45 1.48 3350 1500 2.50 1.49 3820 1500 2.85 1.49 4000 1532 3.04 1.52 4320 1636 3.46 1.60 4860 1714 4.06 1.67 5240 1800 4.66 1.75 5630 1947 5.20 1.85 1.86 8000 2571 9.53 2.38 2.08

23 0.1 1440 3110 2.24 1.44 1.03 3100 1440 3290 2.41 1.47 3280 1470 3440 2.54 1.48 3780 1500 2.82 1.49 4340 1565 3.37 1.55 4740 1636 3.82 1.61 5260 1714 4.42 1.68 1.78 5980 2117 5.85 1.96 1.92 6280 2250 6.46 2.06 2.02 8000 2769 10.03 2.51 2.11

24 0.1 1440 3200 2.30 1.44 1.03 3230 1440 3380 2.48 1.47 3530 1500 3620 2.70 1.49 3880 1500 2.89 1.49 4190 1565 3.24 1.55 4380 1600 3.45 1.58 4790 1636 3.86 1.61 5110 1800 4.40 1.72 1.82 5400 1894 4.85 1.80 1.84 5980 2117 5.89 1.97 1.92 9000 3000 12.29 2.73 2.18

25 0.1 1470 3180 2.34 1.47 1.03 3180 1470 3380 2.53 1.50 3330 1500 3550 1500 2.65 1.50 3810 1565 2.95 1.55 4100 1636 3.29 1.61 4430 1714 3.70 1.67 4600 1800 3.99 1.73 4780 1894 4.31 1.80 1.84 4960 2117 4.78 1.93 1.90 5260 2769 5.95 2.26 2.03 5900 3272 7.86 2.66 2.16 7790 4000 14.55 3.74 2.36 9000 4500 16.97 3.77 2.37

255 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) ( m.s'* ) ( msec ) (km) ( km.s'* ) (Mg.m-")

26 0.1 1470 4850 3.56 1.47 1.03 4860 1470 4920 3.63 1.48 5120 1500 3.83 1.50 5400 1530 4.11 1.52 5500 1565 4.25 1.55 5590 1636 4.44 1.59 1.70 6190 1714 5.13 1.66 1.75 7650 2117 7.55 1.98 1.93 10000 2571 11.88 2.38 2.08

27 0.1 1470 4820 3.54 1.47 1.03 4850 1470 5230 3.91 1.50 5260 1500 5460 4.09 1.50 5630 1500 4.21 1.50 5930 1565 4.59 1.55 6080 1600 4.78 1.57 6190 1675 5.01 1.62 6640 1714 5.50 1.66 1.75 7350 2055 6.93 1.89 1.87 10000 2400 11.12 2.22 2.02

28 0.1 1470 4800 3.53 1.47 1.03 4830 1470 5220 3.90 1.50 5250 1500 5525 4.23 1.53 5700 1565 4.42 1.55 5880 1676 4.76 1.62 6270 1714 5.19 1.66 1.75 6560 1800 5.64 1.72 1.79 6900 1894 6.19 1.79 1.84 8400 2183 8.58 2.04 1.94 10000 2400 11.23 2.25 2.03

29 0.1 1470 4790 3.52 1.47 1.03 4810 1470 5110 3.81 1.49 1.58 5170 1500 5440 4.08 1.50 1.60 5430 1500 5580 1532 4.24 1.52 1.63 6140 1600 4.85 1.58 1.71 6640 1757 5.62 1.69 1.77 7180 1894 6.47 1.80 1.84 7670 2000 7.24 1.89 1.87 8640 2250 9.02 2.09 1.94 10000 2400 11.19 2.24 2.03

256 Interval Panel TWT Velocity. time depth Velocity Density Numbers ( msec ) ( m.s^ ) (msec) (km) ( km.s‘* ) (Mg.m")

30 0.1 1500 4790 3.59 1.50 1.03 4820 1500 5100 3.82 1.50 5300 1500 5660 4.32 1.53 1.64 5700 1532 4.36 1.53 1.64 5910 1565 4.59 1.56 1.69 6140 1565 4.77 1.56 1.69 6260 1636 5.00 1.60 1.73 6520 1714 5.40 1.66 1.75 6770 1847 5.89 1.74 1.79 7500 2000 7.02 1.87 1.86 10000 2400 11.17 2.23 2.02

31 0.1 1500 4800 3.60 1.50 1.03 4810 1500 5100 3.82 1.50 5100 1500 5700 4.43 1.56 1.69 5700 1565 6080 1565 4.33 1.56 1.69 6290 1636 5.05 1.61 1.73 6760 1800 5.82 1.72 1.81 6930 1894 6.18 1.78 1.83 7160 2000 6.64 1.86 1.85 10000 2400 11.18 2.24 2.03

32 0.1 1440 4770 3.43 1.44 1.03 4800 1440 5140 3.79 1.48 1.57 5280 1500 5475 4.11 1.50 1.61 5820 1532 4.43 1.52 1.63 6000 1565 4.64 1.55 1.66 6270 1675 5.08 1.62 1.74 6430 1714 5.31 1.65 1.77 7080 1894 6.34 1.79 1.84 7560 2000 7.10 1.88 1.87 8230 2117 8.16 1.98 1.93 10000 2400 11.18 2.24 2.03

257 F.2 Results of Density Analysis of Rock samples from the Sula Region

Density measurements made by weighing in water and air, in the offices of the Geological Research and Development Centre, Bandung, using samples obtained in the course of the Sorong Fault Zone Project.

No Sample Longitude Latitude Density range Remarks m CS) (Mg.m-') 1 TAOS 124.76 1.81 2.60 - 2.65 Altered basic rock 2 TAIO 124.91 1.82 2.52 - 2.62 Granite (reworked?) 3 TA06.1 124.66 1.85 2.62 - 2.79 Basic (altered?) 4 TA06.2 124.66 1.85 2.38-2.71 Basic (altered?) 5 TA02 124.39 1.89 2.54-2.60 Granite (reworked?) 6 MAOl 124.41 1.83 2.71-3.08 Tectonised ultrabasic 7 MA02 125.50 1.82 2.16-2.32 Volcaniclastic

F3 Density values obtained from a commercial source

This tabulation illustrates the variety of methods being used commercially to estimate rock densities in eastern Indonesia.

No Interval Density or range (Mg.m'^) Source 1 Quaternary 1.6- 1.9 Modelling 2 Surface - Top Eocene 2.0 - 2.11 Modelling/sample testing 3 Accretionary Prism 2.2-2.3 Guestimate 4 Upper thrust sheet 2.12 Sample testing 5 Mud volcano outflow 1.7-1.75 Modelling 6 Eocene 2.41 Sample testing 7 Base Tertiary - Albian 2.18 Well logs 8 Paleogene 2.25 Company standard value 9 Mesozoic 2.3-2.5 Modelling 10 Paleozoic 2.68 Well/modelling

258