Solomon Islands

SOPAC/GA Tsunami Hazard Assessment Project Report 04

INVENTORY OF GEOSPATIAL DATA AVAILABLE AND OPTIONS FOR TSUNAMI INUNDATION & RISK MODELLING

SOLOMON ISLANDS

Helen Pearce ([email protected])

SOPAC Miscellaneous Report 654

January 2008

[2]

Compiled by

Helen Pearce

Ocean & Islands Programme SOPAC Secretariat

This report may also be referred to as SOPAC Miscellaneous Report 654

Copies of this report may be obtained from:

SOPAC Secretariat Private Mail Bag GPO, Suva Fiji Islands Phone: (679) 3381377 Fax: (679) 3370040 http://www.sopac.org E-mail: [email protected]

[SOPAC Miscellaneous Report 654 – Pearce] [3]

TABLE OF CONTENTS

Acknowledgements...... 4 Acronyms...... 4

1 Introduction ...... 5

2 Sources of Tsunami Hazard ...... 6

3 Vulnerability/Exposure...... 8

4 Overview of Tsunami Hazard Affecting the Southwest Pacific...... 10 (i) Summary Extracts ...... 10 (ii) Summary and Interpretation for Solomon Islands ...... 14 (a) Composite of Deep-Water Tsunami Generated by 8.5 Mw Sources around the Pacific .....14 (b) Composite of Deep-Water Tsunami Generated by 9.0 Mw Sources around the Pacific .....15

5 Data Available at SOPAC for Inundation Modelling ...... 16 (i) Bathymetry Datasets and Marine Charts...... 16 (ii) Satellite Imagery ...... 26 (iii) Topography, Coastline and Reefs ...... 26 (iv) Infrastructure Data ...... 27 (v) Post Tsunami Inundation/Run-Up Data...... 27 (vi) Data Summary...... 30

6 Summary ...... 32

7 Bibliography ...... 33

Appendix 1: Datum and Definitions ...... 35 1 Datum and Geodetic Levels at Honiara...... 35 2 Topographic Dataset Issues for PICs...... 36 3 Definitions and Acronyms...... 37

Appendix 2: Historical Tsunami Events affecting Solomon Islands ...... 44 1 Previous Tsunami that have been Recorded in the Solomon Islands...... 44 2 Recent PTWC Warnings...... 46 3 Tsunami Warning Related Background...... 59 (i) Summary of JMA/PTWC Causal Earthquake Criteria ...... 59 (ii) Tsunami Hazard Sources ...... 60 (iii) Real-Time Sea Level Data Available for Tsunami Monitoring...... 61

Appendix 3: Additional Modelling ...... 64 1 Modelling of Major Tsunami for Sources around the Pacific...... 64 2 Most Scenarios for Sources Affecting the Solomon Islands...... 70

[SOPAC Miscellaneous Report 654 – Pearce] [4]

ACKNOWLEDGEMENTS

The assistance of Mary Power, Arthur Webb and Jens Kruger of SOPAC, Phil Cummins, Chris Thomas and Jane Sexton of Geoscience Australia, Ruth Broco of NGDC Tsunami Database and project funding from AusAID is gratefully acknowledged.

ACRONYMS

ABoM Australian Bureau of Meteorology AHO Australian Hydrographic Office ATAS Australian Tsunami Alert Service (superceded by JATWC) CD Chart Datum DART Deep-ocean Assessment and Reporting of Tsunami. DEM Digital Elevation Model DSM Digital Surface Model EEZ Economic Exclusion Zone GA Geoscience Australia GNS Institute of Geological and Nuclear Sciences, New Zealand GTS Global Telecommunications System HAT Highest Astronomical Tide IOC Intergovernmental Oceanographic Commission ITIC International Tsunami Information Centre JMA Japan Meteorological Agency JATWC Joint Australian Tsunami Warning Centre LIDAR Light Detection and Ranging LAT Lowest Astronomical Tide MOST Method of Splitting Tsunami ( type of numerical model) MSL Mean Sea Level NGDC National Geophysical Data Centre (NOAA) PIC Pacific Islands Countries PDC Pacific Disaster Centre PTWC Pacific Tsunami Warning Centre SOPAC Pacific Islands Applied Geoscience Commission SPSLMP South Pacific Sea Level and Climate Monitoring Project UNESCO United Nations Educational, Scientific and Cultural Organisation UTC Universal Time Coordinate (also referred to by Z or GMT) UTM Universal Transverse Mercator WGS World Geodetic System WMO World Meteorological Organization

[SOPAC Miscellaneous Report 654 – Pearce] [5]

1 INTRODUCTION

SOPAC and Geoscience Australia, funded by AusAID have established the first component of a multi-stage project to look at tsunami hazard and risk assessment in the southwest Pacific. As part of that project Geoscience Australia have produced a tsunami hazard assessment for the Southwest Pacific based on a deterministic deep-water tsunami propagation model (A Preliminary Study into the Tsunami Hazard faced by southwest Pacific, Thomas et al. 2007). That report is available at via the Pacific Disaster Net (http://www.pacificdisaster.net/drm/). In parallel with that component of the project a review of data available for inundation modelling in the Southwest Pacific is being conducted by SOPAC, as inundation modelling requires significantly higher- resolution bathymetry, inter-tidal and coastal topography than the deep-water propagation models.

Deep-water models alone are not sufficient to develop a detailed understanding of tsunami inundation on coastlines and ultimately it is proposed that the deepwater model output will be used to define the boundary conditions to allow more detailed, site-specific tsunami inundation modelling of key and priority PIC coastal areas. The combination of the deepwater propagation and inundation model output will then be used to provide information and tools for emergency management and infrastructure planning in the Southwest Pacific. However, detailed tsunami inundation modelling can only be undertaken if bathymetry (seafloor mapping) and topographic (land elevation or height) data of adequate quality and coverage exist.

SOPAC, through EU-funded projects, has been addressing some of the needs in the Pacific region for high-resolution bathymetry data. This data is underpinning a number of critical technical projects in the areas of marine boundaries, fisheries, coastal processes, and in hydrodynamic modelling for projects in support of reducing impacts of aggregate mining etc. However there is very little in the way of high-resolution coastal and inter-tidal topography data available in the Pacific region that is suitable for inundation and sea-level change modelling and monitoring. There is a distinct possibility that the issue of inadequate topographic data in many Pacific Island Countries (PICs) and the limiting effect this may have on tsunami and other inundation modelling may require consideration of options to improve coastal topographic data collection by methods such as LIDAR.

This report for Solomon Islands is the fourth in a series of reports and reviews the availability of high-resolution inshore bathymetry and also inter-tidal and coastal topography of low-lying coastal areas. The reports completed so far (Pearce, 2007a-c) are available through the Pacific Disaster Net and the SOPAC virtual library.

Geographical information and location of Solomon Islands are at Table 1 and Figure 1.

Table 1: Geographic Information for Solomon Islands. (http://www.sopac.org/tiki/tiki-index.php?page=Solomon+Islands).

Capital: Honiara Population: 409, 042 (1999) Land Area: 28, 785 sq. kilometres Max Height (above Sea–level): 2, 447 m (Mt. Makarakombou) EEZ: 1, 340, 000 sq. kilometres

Rainfall: Varies from 3,000 – 5,000 mm per annum Mean Temperature: 26°C GDP per Capita: SB $584 (2002) Currency: Solomon Island Dollar (SB$) Languages: English (official), Pidgin and 87 other languages Government: Independent State and Member of the Commonwealth SOPAC Membership: Founding member since 1971 (then CCOP/SOPAC)

[SOPAC Miscellaneous Report 654 – Pearce] [6]

Figure 1: Location of Solomon Islands.

2 SOURCES OF TSUNAMI HAZARD

Major subduction zones are the predominant source of earthquakes large enough to generate regional or ocean-wide tsunami. They are the main focus of the preliminary hazard analysis report (Thomas et al. 2007), which models magnitude 8.5 and 9.0 earthquake source tsunami generation (as discussed in section 4). The location and names of these subduction zones are shown in Figure 2. The Solomon Islands are located very close to a major source, the South Solomons Trench.

Tsunami can also be generated from other processes such as meteors, volcanic eruption, volcanic collapse and submarine landslide. The latter are often triggered by earthquakes and are commonly attributed to the earthquake. Steep-sloped bathymetry on volcanic and other islands and submarine volcanoes may have the potential to slump or collapse and depending on the size of such collapses these events may cause local tsunami. The location of the three major volcanoes in the Solomon Islands – Kavachi, Savo and Tinakula are shown at Figure 3. Small tsunami were observed from Kavachi in 1955 and from Tinakula in 1966 and 1971.

A table of the causal earthquake criteria for local, regional and ocean-wide tsunami (i.e. 100 km, 1000 km, >1000 km) and the range of expected destructive impact, similar to that used for warning purposes by the Japan Meteorological Agency (JMA), Pacific Tsunami Warning Centre (PTWC) and Australian Tsunami Alert Service (ATAS) is described in Appendix 2 Section 2. The PTWC Bulletins are issued as advice to government agencies. Only national and local government agencies have the authority to make decisions regarding the official state of alert in their area and any actions to be taken in response.

There has been sea level recording site in Honiara since 1992, operated by the Australian Bureau of Meteorology (ABoM). Recorded historical earthquake and volcanic generated tsunami events affecting the Solomon Islands are discussed at Appendix 2, along with examples of PTWC bulletins issued for the 2 April 2007 tsunami and the smaller Santa Cruz 2 September 2007 tsunami. The period of records available is short compared to the recurrence interval of large events on the South Solomons Trench. More work could be done to collect paleo-seismic and paleo-tsunami

[SOPAC Miscellaneous Report 654 – Pearce] [7] information and oral history of tsunami in the region to assist with estimates of probabilities of events associated with that source.

Figure 2: Map of major plate boundaries in the Pacific Ocean with subduction zones labelled as follows: AlT– Aleutian Trench, ChT– Chile Trench, CsT– Cascadia Trough, HT– Hikurangi Trough, IBT– Izu Bonin Trench, JpT– Japan Trench, KmT– Kermadec Trench, KrT– Kuril Trench, MT– Mariana Trench, MAT– Middle America Trench, NT– Nankai Trench, NGT – New Guinea Trench, NHT– New Hebrides Trench, PhT– Philippines Trench, PrT– Peru Trench, PyT– Puysegur Trench, RT– Ryukyu Trench, SST– South Solomons Trench, TnT– Tonga Trench. Subduction plate margins are shown in blue and are the source of the largest earthquakes in history (Thomas et al. 2007). The location of the Solomon Islands is marked in purple.

Figure 3: Major volcanoes in the Solomon Islands.

[SOPAC Miscellaneous Report 654 – Pearce] [8]

3 VULNERABILITY/EXPOSURE

The Solomon Islands are located very close to the South Solomons Trench (henceforth referred to as Solomons Trench) to the southwest and the northern part of the New Hebrides Trench to the south. They are also vulnerable from the northwest from the Mariana, Western Aleutian and Nankai Trench sources.

Any local, regional or ocean-wide event generated by the Solomons Trench would reach parts of Solomon Islands with minimal formal warning lead time, apart from feeling the earthquake. Any regional or ocean-wide event from the New Hebrides Trench and eastern Papua New Guinea (still part of Solomons Trench) would reach parts of the Solomon Islands within three hours. Any ocean- wide event from the northwest sources would have four to ten hours lead time for a warning to be disseminated.

The major island or submarine volcanoes are potential sources of local tsunami. One of these, Savo, is located only 35 km north-northwest of Honiara, the capital city of the Solomon Islands. Honiara a relatively highly populated area. It would be potentially vulnerable to any landslide generated tsunami from this source.

All the significant recorded tsunami run-up events in the Solomon Islands have been generated from the Solomons Trench e.g. the recent 2 April 2007 event near Ghizo, Beaufort Bay on the west coast of Gaudalcanal in 1939 and San Cristobal Island in 1931, Gaudalcanal in 1961 and Choiseul 1974 (Table A2-1).

The 2 April 2007 tsunami reached parts of the coast within ten minutes of the earthquake (Figure 4). This is insufficient lead time for formal warnings to be effective. Villagers very close to the source of the earthquake need to rely on public education, feeling the earthquake and self evacuation where appropriate. The further a region is from the source the more lead time is available to facilitate formal warning process, e.g. the tsunami travel time to Honiara was approximately forty minutes and to Kirakira on San Cristobal Island approximately fifty six minutes.

Figure 4: Post-tsunami modelling at ten minutes after the 2 April 2007 earthquake, showing extremely short lead time before the tsunami generated on the South Solomons Trench reached populated areas of Solomon Islands. Red represents wave peak, blue the wave trough (Tomita et al. 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [9]

The prior knowledge of potential impacts from various sources, both close to and distant from the Solomon Islands, is therefore critical. With the deepwater modelling as input into island-specific, finer-resolution tsunami inundation models, a greater understanding of the potential risk and possible impacts of tsunami may be realised. It will then be extremely important for communicating the comparative risks and consequences within all-hazard frameworks and action plans. It should be noted however that accurate detailed tsunami inundation modelling can only be undertaken where adequate bathymetric (seafloor mapping) and topographic (land height or elevation) information exist.

Tsunami generating mechanisms are themselves not known to be impacted by climate change directly. However, climate change may impact indirectly (Figure 5) by reducing the innate resilience of coastal systems; e.g. increased sea level, erosion, etc. and thereby, leave coastal communities in a position of greater vulnerability. A further consideration is the timing of tsunami with sea state and high tides; e.g. if a tsunami arrives during a spring low tide the impacts would be less than if it arrived during a spring high tide (Appendix 1 Section 3).

Figure 5: Tsunami generation is not directly influenced by climate change, however climate change indirectly influences impact (Glassey et al. 2005).

[SOPAC Miscellaneous Report 654 – Pearce] [10]

4 OVERVIEW OF TSUNAMI HAZARD AFFECTING SOUTHWEST PACIFIC

A deterministic broad-scale tsunami hazard assessment for the southwest Pacific based on the deep-water tsunami propagation model was conducted (Thomas et al., 2007) by Geoscience Australia focusing on the major subduction zone sources (Figure 2) around the Pacific. Section (i) below contains summary extracts from that report and section (ii) contains extracts specific to Solomon Islands and some added interpretation. Solomon Islands were ranked Category 5 (Suite 1) and 5 (Suite 2) in the preliminary deep-water tsunami hazard study (these categories are explained below).

(i) Summary Extracts:

“To aid in interpretation of the results, offshore tsunami amplitudes have been categorized into 5 ranges (Table 1). Categories corresponding to a higher range of offshore tsunami amplitudes can presumably be associated with a higher level of hazard on coastlines of similar type. This categorization has been adopted throughout this report. It is important to note, however, that these ranges do not reflect the inundation that normally causes damage and/or fatalities and which can often vary widely depending on local bathymetry and topography. The categories indicated in Table 1 are therefore best viewed as indicating a relative level of hazard over areas of broad geographic extent. For example, a Category 5 tsunami along the coast of Papua New Guinea represents a higher level of hazard than a Category 2 tsunami along the coast of New Caledonia.

It is premature, however, to interpret Table 1 in terms of impacts. This is especially true for low-lying atolls such as Tuvalu and Kiribati. On the one hand, the lack of any high ground may appear to make these islands especially vulnerable to tsunami, so that even a Category 2 tsunami may be a cause for serious concern. On the other hand, because such atolls often have steep drop-offs in which ocean depths increase very rapidly with distance from the fringing reef, there may not be a pronounced shoaling effect, so that these islands may never experience a large tsunami. Such considerations require much more modelling to address and are beyond the scope of the present study, although it is intended that they be considered in a later phase of this project. In particular, the information presented in this report should not be used as a guide for responding to tsunami warnings. The information presented here is preliminary and is only intended as a rough guide for prioritizing work in subsequent phases of this project.

Table 1: Categorisation of offshore tsunami amplitudes, normalised to equivalent depth of 50metres. The “Colour “ column refers to the colour used for amplitudes of this category which have been used throughout this report

Tsunami generated by two suites of simulated earthquakes were studied: Suite 1, consisted of 187 moment magnitude (Mw) 8.5 earthquakes, and Suite 2 comprised 39 Mw 9.0 earthquakes (Figures 5 and 7, pages 11 and 13). The results are summarised in Table 2. For both suites of earthquakes the nations most affected were in the south and west of the study area, including Vanuatu, Papua New Guinea, Guam, Solomon Islands and Tonga, each of which recorded Category 5 amplitude tsunami from the Suite 1 (Mw 8.5 earthquakes). This is due to the proximity of these countries to the subduction zones and the orientation of the fault lines which acts to direct the tsunami towards these nations”…

… Nations in the north and east of the study area, such as Kiribati, Marshall Islands, Nauru, Cook Islands, French Polynesia and Tuvalu were much less affected by the Suite 1 tsunami and only experienced Category 1 or 2 sized waves. As is to be expected, Suite 2 events produced greater effects than those of Suite 1 on all nations. Notable in this respect is Fiji which experienced Category 5 amplitudes from Suite 2 events. However it should be

[SOPAC Miscellaneous Report 654 – Pearce] [11] noted that without further investigation it is not possible to say that even Category 2 amplitudes will not produce significant run-up at some locations.

The figures in Appendix A show that Suite 1 events (Mw = 8.5) from the subduction zones in the eastern and far northern rims of the Pacific did not produce effects larger than Category 2 on any of the nations studied. However some Suite 2 events (Mw = 9.0) in the Peru-Chile, Aleutians and Kuril subduction zones did produce Category 3 or above effects for some nations

Table 2: Summary of results. Categories represent the highest amplitude recorded for that nation, and should be interpreted according to Table 1.

….Events from Suite 1 in the subduction zones of the east, north and northwest rim of the Pacific have less effect on the region, either because of their distance, because the orientation of the fault lines acts to direct tsunami energy away from the region, or because of intervening bathymetric features. They rarely produced normalised amplitudes greater than Category 1, and never greater than Category 2.

[SOPAC Miscellaneous Report 654 – Pearce] [12]

Table 3: Most significant source regions for each nation, based on model out put points that recorded a maximum amplitude exceeding 75 centimetres for Suite 1 (Mw 8.5).

….This modelling pays no regard to the probability of events of various magnitudes occurring on any of these subduction zones. While there is no doubt that the Chile sub-duction zone can host an earthquake exceeding Mw 9.0 (the 1960 event was magnitude 9.5) there is as yet no consensus on a reliable method of determining the absolute maximum magnitude on any given subduction zone. We believe that most seismologists would agree that a magnitude 8.5 event is plausible on any of the subduction zones considered here, and that a 9.0 event is impossible to rule out. Hence we consider both magnitudes. A probabilistic tsunami hazard study would consider a range of earthquake magnitudes and weight them according to estimates of their likelihood, in a similar way to the method described in Burbidge et al, (2007).

….Like Suite 1, the nations most affected by the Suite 2 events were those in the south and west of the study area, as a result of the subduction zones in that region. However the plots in Appendix A show that Suite 2 events in the Chile-Peru, Cascadia, Aleutians and Kuril subduction zones produced significant (Category 3 or above) normalised amplitudes for some nations. For example the simulations indicate that the Chile-Peru zone is a significant source of hazard from Mw 9.0 events for Fiji and French Polynesia, as are the Aleutian and Kuril subduction zones for Guam, Federated States of Micronesia, Papua New Guinea, the Solomon Islands and Vanuatu. Significant normalised amplitudes were produced in Papua New Guinea and the Solomon Islands from modelled events in the Cascadia Subduction Zone.

[SOPAC Miscellaneous Report 654 – Pearce] [13]

Table 4: Most significant source regions for each nation, based on model out-put points that recorded a maximum amplitude exceeding 75 centimetres for Suite 2 (Mw 9).

[SOPAC Miscellaneous Report 654 – Pearce] [14]

(ii) Summary and Interpretation for Solomon Islands

(a) Composite of Deep-water Tsunami generated by 8.5 Mw Sources around the Pacific Based on Figures 6 and 7 below, for an 8.5 Mw generated tsunami event, the Solomons Trench source has the potential to generate deep-water tsunami of Categories 4 and 5 for parts of the Solomon Islands. The northern New Hebrides Trench source has the potential to produce Category 3. The New Guinea, southern New Hebrides, Mariana, and parts of Kuril, Western Aleutian, Northern Tonga and Kermadec trenches sources have the potential to produce Category 2. Other more distant sources, only have the potential for Category 1.

Figure 6: Composite of normalised source 8.5 Mw deep-water tsunami for the Pacific. Maximum wave heights for the 187 tsunami of suite normalised to a standard depth of 50 m using Green's Law (Thomas et al. 2007).

Figure 7: Magnitude 8.5 earthquakes ranked by the Category of offshore tsunami they could cause in the Solomon Islands. Each bar is displayed at the position of a magnitude 8.5 earthquake for which a tsunami was modelled, and the height and colour of the bar indicates the Category (Section 4, Table 1.) of the offshore tsunami modelled in Solomon Islands (Thomas et al. 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [15]

(b) Composite of Deep-water Tsunami generated by 9.0 Mw Sources around the Pacific . Based on Figures 8 and 9 below, for a 9 Mw generated tsunami event, the South Solomons Trench source has the potential to generate deep-water tsunami of Category 4 and 5 for parts of the Solomon Islands. The New Hebrides to the south and Mariana, Western Aleutian, Nankai and Kuril, sources to the northwest, have the potential to generate category 3 for parts of the Solomon Islands. Japan, Izu-Bonin, Philippines, Central Aleutian, Cascadia, Peru and parts of Chile trenches have the potential to produce Category 2. The other sources have only the potential to generate Category 1.

Figure 8: Composite of normalised source 9 Mw Tsunami for Pacific. Maximum wave heights for the 39 tsunami normalised to a standard depth of 50 metres using Green's Law (Thomas et al. 2007).

Figure 9: Magnitude 9 earthquakes ranked by the Category of offshore tsunami they could cause in the Solomon Islands. Each bar is displayed at the position of a magnitude 8.5 earthquake for which a tsunami was modelled, and the height and colour of the bar indicates the Category (Section 4 Table 1.) of the offshore tsunami modelled in Solomon Islands (Thomas et al. 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [16]

5 DATA AVAILABLE AT SOPAC FOR INUNDATION MODELLING

Global bathymetry and topography datasets were sufficient for the deep-water tsunami modelling used in the preliminary hazard assessment (Thomas et al. 2007). However inundation modelling, as does storm surge modelling, requires significantly higher resolution bathymetry as well as inter- tidal and coastal topography than the deep-water propagation models.

A review of the data available at SOPAC to support inundation modelling has been conducted.

(i) Bathymetry Datasets and Marine Charts

Global Deep Water Bathymetry

S2004 (Global 1 minute, ~2 km): Available via ftp from ftp://falcon.grdl.noaa.gov/pub/walter/Gebco_SandS_blend.bi2. S2004 merges the satellite altimeter data derived Smith and Sandwell (1997) grid with GEBCO over shallow depths (Marks and Smith, 2006).

Hydrographic Charts A range of hydrographic charts at various scales is listed below with examples of coverage in Figures 10-12.

Savo

Honiara

Figure 10: Sealark Channel and Approaches to Honiara: Datum Lat Mercator, WGS 72 1:100,000 at Lat 9 15S. Also shows the location of the volcano Savo approximately 35 km from Honiara.

[SOPAC Miscellaneous Report 654 – Pearce] [17]

Beaufort Bay

Figure 11: Extract from Indispensable Strait 1:300,000 Mercator chart showing bathymetry of Guadalcanal and location of Beaufort Bay which had a recorded 10.5 m tsunami on 30 April 1939.

Figure 12: Extract of Ghizo Region from Choiseul Island to New Georgia Island (1979): Mercator, Datum LAT, WGS72, 1:300,000.

Approaches to Ghizo Harbour (1976) 1:25,000 Projection Gnomonic DOS (1964) Datum: MHHW (not scanned)

Ghizo Harbour (1976) 1:12,500, Projection Gnomonic DOS (1964) Datum: MHHW (not scanned)

[SOPAC Miscellaneous Report 654 – Pearce] [18]

Fair-sheets A range of additional bathymetry data is available from the Australian Hydrographic Office (AHO) (Figures 13 & 14) and the Solomon Islands Hydrographic Office (Figure 15) Fair Sheet holdings. Some of this data is in digital form and some are scanned hand-drawn plots.

Figure 13: GA holdings of AHO Fair Sheet data.

Figure 14: More detailed view of AHO Fair Sheet holdings for area between Guadalcanal and Malaita.

[SOPAC Miscellaneous Report 654 – Pearce] [19]

Figure 15: Solomon Islands Hydrographic Office Fair Sheets for Ghizo area.

Other bathymetry Surveys

RV L'Atalante survey data using a Simrad EM12 multibeam system, during the SOPACMAPS Project, Leg 2, 19 August to 16 September 1993. Shown as contours without colour on Figure 18.

Single beam survey Marovo by University of Queensland (2005) shown in Figure 20.

SOPAC/EU Surveys SOPAC conducted bathymetry surveys in June and July 2005 covering Honiara, Marovo, Noro and Ghizo. The locations are shown in Figure 16 and in more detail in Figure 17 and the bathymetry data at Figures 18 to 21. The background to priority of the surveys for the various locations:

• Ghizo: area is relevant for aquaculture/pearl farming, tourism and marine protected areas. • Iron Bottom Sound (Honiara): Bathymetric survey to obtain physical oceanographic data in order to generate management maps and hydrodynamic models to identify and manage risk of oil leakage from war relics and sewage outfall from Honiara. • Marovo Lagoon: Generate management maps and hydrodynamic models to track dispersal of silt from deforestation on Vangunu. This area is a proposed World Heritage site important for tourism and fisheries. • Noro: Survey to characterise pollution from fish cannery and provide baseline information for a hydrodynamics model.

Information on coverage area and maximum depth are at Table 2 and formats of datasets at Table 3.

[SOPAC Miscellaneous Report 654 – Pearce] [20]

Table 2: Locations of SOPAC/EU bathymetry surveys.

Location Area covered by MBES Maximum depth of coverage Ghizo Up to 2 km off the barrier reef with shallow water coverage inside the 500 m reef system. Honiara 40 km offshore 1150 m Marovo 5 km inside the reef systems 500 m Noro 7.5 km off the eastern barrier reef 400 m

4°S

6°S

8°S Gizo Marovo SOLOMON Noro Honiara 10°S ISLANDS

12°S

14°S

16°S 156°E 158°E 160°E 162°E 164°E 166°E 168°E 170°E 172°E

Figure 16: Solomon Islands EEZ showing locations of recent SOPAC/EU surveys.

Figure 17: Locations of recent SOPAC/EU bathymetry surveys in Western and Central Guadalcanal regions (Kruger & Sharma 2007, in prep).

[SOPAC Miscellaneous Report 654 – Pearce] [21]

Table 3: Formats for SOPAC/EU bathymetry survey data.

There is reasonable bathymetry coverage around Ghizo and Honiara however there are gaps in the inshore shallow areas. Satellite-derived bathymetry (from QuickBird or other satellites) could be an option for filling in gaps in coverage. Satellite bathymetry usually is only viable for depths less than 20 m. The timeframe and effectiveness of this option needs to be investigated further to establish viability and cost effectiveness.

[SOPAC Miscellaneous Report 654 – Pearce] [22]

Figure 18: SOPAC/EU Honiara Survey with previous 1993 survey contours shown without colour (Kruger & Sharma 2007, in prep).

[SOPAC Miscellaneous Report 654 – Pearce] [23]

Figure 19: SOPAC/EU bathymetry for Ghizo (Kruger & Sharma 2007, in prep.).

[SOPAC Miscellaneous Report 654 – Pearce] [24]

Figure 20: SOPAC/EU bathymetry for Marovo (Kruger & Sharma 2007, in prep.).

[SOPAC Miscellaneous Report 654 – Pearce] [25]

Figure 21: SOPAC/EU bathymetry for Noro (Kruger & Sharma 2007, in prep.).

[SOPAC Miscellaneous Report 654 – Pearce] [26]

(ii) Satellite Imagery

Landsat data is available for the Solomon Islands at 30 m resolution.

SOPAC has also purchased QuickBird pan-sharpened (60 cm resolution) data for:

Island Area (Km Sq) Vella Lavella 327 Ranonga 262 Ghizo 267 Kolombangara 236 Rendova 281 and IKONOS imagery for Ghizo, as the QuickBird image was of poor quality due to cloud cover.

(iii) Topography, Coastline and Reefs

(a) Topographic Maps are available at: 1:50,000 (1968-75) with 20 m contours (including Honiara and Ghizo) 1:10,000 with (1969-1975) 10 m contours (datum MHWM 0.2 m above MSL) 1:2,500 (1969-1975) Parts of Honiara township (datum MHWM 0.2 m above MSL)

(b) Contours at 20 m intervals digitised from 50,000 topographic maps.

(c) Coastline defined as (MSL or MHWM) and reefs digitised from topographic maps and varying resolution satellite imagery. Sources and metadata not available. This may need to be redone from Quickbird imagery.

(d) DEM/DSM • Space Shuttle Topography Mission 90 m grid for all of Solomon Islands, WGS84, Geodetic, MSL. Data Directory: http://seamless.usgs.gov. This is far too coarse for inundation modelling requirements.

• Digital Surface Model (DSM) with 5 m vertical accuracy available in Solomon Islands. Specifications at Table 4 below.

The accuracy of the topography in the range MSL to 5 m has a significant impact on the quality and credibility of any tsunami inundation modelling. The Digital Surface Model represents the tops of trees and buildings rather than the ground as per a Digital Elevation Model (DEM) or Digital Terrain Model (DTM). The satellite DEM is too coarse and the suitability of the DSM for inundation modelling will be limited unless additional information is available to better define the low-lying topography in critical areas.

[SOPAC Miscellaneous Report 654 – Pearce] [27]

Table 4: Metadata for DSM.

(iv) Infrastructure data

Honiara was part of the Pacific Cities Project in 1998. This project collected infrastructure data in GIS format for a number of Pacific Cities. It would need some updating from satellite imagery. Ghizo was not part of Pacific Cities Project therefore infrastructure data is limited, however it could also be supplemented from satellite imagery.

(v) Post-tsunami inundation/run-up data

The only international sea-level monitoring gauge is in Honiara. Although it recorded the tsunami it was outside the main affected area. After the 2 April 2007 tsunami event a number of international technical survey teams measured tsunami run-up, inundation and land level changes in the most affected areas. Figure 22 shows the survey points for the McAdoo team, Nishimura team and Tomita team surveys and are discussed in McAdoo et al. 2007. Figure 23 the run-up and inundation heights from the Tomita survey (Tomita et al. 2007). Figure 24 shows the locations and heights for the Fritz team (Fritz & Kalligeris 2008) survey:

These surveys results will provide an excellent opportunity to calibrate and verify any inundation modelling undertaken for this region.

[SOPAC Miscellaneous Report 654 – Pearce] [28]

Figure 22: Location of post 2 April tsunami event surveys for three teams.

Figure 23: The post-tsunami survey information on run-ups and inundation heights (metres) from the 2 April 2007 tsunami in Solomon Islands (Tomita et al. 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [29]

Figure 24: Post 2 April 2007 tsunami survey information (Fritz & Kalligeris, 2008). Measured tsunami run-up (red) tsunami heights (blue) and land level changes (green).

[SOPAC Miscellaneous Report 654 – Pearce] [30]

(vi) Data Summary

Table 5: Summary of available data.

Type Resolution Metadata available Datum/Projection Format Bathymetry S2004 Global 1 minute, ~2 km Yes WGS 84/MSL ASCII grid, xyz

Deep-water Multibeam Various Yes UTM 57S,WGS 84,/LAT xyz Survey data

AHO Fair Sheets Various Yes Mercator/UTM Zone 57S, WGS 72/ Contours only LAT RV L'Atalante 1993 50 m contours

Honiara Various Ghizo Marovo Noro

Grid created from survey Surfer .grd) data Honiara 100 m Ghizo 20 m Marovo 20 m Noro 50 m

Contours Mapinfo Backdrop 10 m to 50 m then 50 m Mapinfo intervals Marine charts Honiara 1:300,000 & 1:2,500 Yes Mercator/UTM Zone 57S, WGS 72/ Paper/scanned Ghizo 1:100,000 LAT Paper/scanned 1:25,000 Satellite derived Could be option to fill None yet bathymetry in gaps Coastlines

Outline Various No UTM Zone 57S, WGS 84, MSL or MapInfo LAT? Lines Reefs Platform No UTM Zone 57S, WGS 84 Topography Topographic maps All Solomon Islands 1:50,000 (1968-75) with UTM 57S, WGS 72, MSL Paper Chart 20 m contours (including Honiara and Ghizo)

Honiara 1:10000(1969-1975) with 10 m contours (datum MHWM 0.2 m above MSL)

1:2500 (1969-1975) Parts of Honiara township (datum MHWM 0.2 m above MSL)

Digitised Contours Contours Digitised from No MapInfo Lines maps.

Spot values None

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(All Solomon Islands) Satellite DEM 90 m Yes WGS 84,MSL

Digital Surface Model 5 m (Expected to UTM, WGS 84, MSL (DSM) become available)

Imagery Landsat 30 m Yes UTM 57S, WGS 84 Geo-referenced TIF (Mapinfo) QuickBird 0.6 m pan-sharpened Yes Vellalavalle Kanongo Ghizo Kolombangara Rendova

Infrastructure Honiara Digitised from 1:10000 Pacific Cities Project UTM 57S, WGS 84 MapInfo Roads and 1:2500; and satellite CD Lines/polygons Wharf imagery Airport Buildings

Ghizo Digitised from 1:50,000 No UTM 57S, WGS 84 Roads maps and satellite Wharf imagery Airport Buildings

Tsunami Run-up Data Ghizo Various Yes WGS, MSL xyz Rendova Simbo Choiseul Vella Lavella

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6 SUMMARY

There are three main issues that will influence the priorities for, and ability to do, tsunami inundation modelling in Pacific:

• Hazard Category from deep-water modelling; • Vulnerability/Exposure; and • Availability of high resolution bathymetry, and inter-tidal and coastal topography data.

The extracts from the National Geophysical Data Centre (NGDC), Tsunami Inundation in Table A2-1, show that for the tsunami that have been recorded all the most significant recorded events are from the Solomons Trench source with a few regional events from eastern Papua New Guinea (still attributed to the Solomons Trench) and Vanuatu (New Hebrides Trench). There were two recorded events from Russia, although the recorded run-ups for these are less than 1 m.

The Solomon Islands are ranked Category 5 for both the 8.5 Mw and 9 Mw for the Solomons Trench source in the preliminary tsunami hazard study based on deep-water modelling (Section 3 and Figure A3-1 (31, 32, and 33)). Travel times to the Solomon Islands from this trench would be very short, providing minimal opportunity for formal warning. Other parts of the Solomon Islands are also vulnerable to Category 3 events from the northwest (Figure A3-1 (15, 16, 23, 25, and 26)); however these would have longer lead times for the formal warning process. The Solomon Islands also has three major volcanos – Kavachi, Savo and Tinakula, which are possible sources of local tsunami. Small tsunamis were observed from Kavachi in 1955 and Tinakula in 1966 and 1971.

The bathymetry and topographic datasets available are not yet complete enough to be suitable for tsunami inundation modelling. There are significant gaps that would need to be addressed with lower resolution sources. There are two areas where datasets could be further developed. These are Ghizo in relation to the Solomons Trench tsunami source scenarios and Honiara in relation to a Savo volcanic cone collapse tsunami scenario. The resolution and quality of the bathymetry datasets between the Solomons Trench source to the south of Guadalcanal and the area around Honiara on the north, which has SOPAC/EU bathymetry data, limits the viability for modelling that source for Honiara. Satellite-derived bathymetry may be a cost-effective way to address gaps in the bathymetry for both Ghizo and near Savo and Honiara.

A bigger issue is the topographic and inter-tidal data. Unfortunately, the available contour maps and the Digital Surface Model (DSM) do not provide adequate definition of low-lying areas. LIDAR data (Appendix 1 Section 2) of the coastal and inter-tidal area would be ideal, but extremely expensive. It is uncertain at this stage whether the DSM can be improved or supplemented and this needs to be investigated further. The cost effectiveness of acquiring extra data or the effect of using poorer resolution data on the results of the modelling would need serious consideration.

The use of deep-water modelling from various sources as input into island-specific, finer- resolution inundation modelling is important for understanding the possible impacts and for communicating the comparative risk and consequences within the all hazard framework and action plans. However this is only possible where the datasets available can be improved to a sufficient quality and resolution to make this viable.

The post-2 April 2007 tsunami surveys of the run-up and inundation in the Ghizo area provide a critical dataset for calibration and validation of an inundation model for the Ghizo area. Geoscience Australia as part of the next stage of the Hazard Assessment Project will be looking at the options for improving the bathymetry and topographic datasets in order to take advantage of the opportunity to use the post-event data to further validate the inundation model results.

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7 BIBLIOGRAPHY

ABoM, 2007. Australian Bureau of Meteorology Web Site. http://www.bom.gov.au

Biukoto, L., Swamy, M., Shorten, G. G., Schmall, S., and Teakle, G. 2001. Pacific Cities CD, Honiara. GIS Hazards Dataset, Version 1.1. SOPAC Data Release

Burbidge, D., Cummins, P. and Mleczko, R. 2007. A Probablistic Tsunami Hazard Assessment for Western Australia. Report to the Fire and Emergency Services Authority of Western Australia, Geoscience Australia.

Cummins, P. 2007. The Solomon Islands Earthquake and Tsunami. Risk Research Group, Geoscience Australia.

Everingham, I. B. 1977. Preliminary catalogue of tsunami for the New Guinea/Solomon Islands region 1768-1972, Dept of National Resources.

Glassey, P., Heron, D., Ramsey, D., & Salinger, J. 2005. Identifying Natural Hazards and the risk they pose to Tonga. GeosourceTonga, Study Report 4.

Fritz, H.M., & Kalligeris, N. (2008). Ancestral heritage saves tribes during 1 April 2007 Solomon Islands tsunami, Geophys. Res. Lett., 35, L01607, doi:10.1029/2007GL031654.

Howorth, R., Elaise, A. 1997. Workshop on Volcanic Hazards and Emergency Management in the South Pacific. SOPAC Miscellaneous Report 245.

IAVCEI Workshop on Ulawun Decade Volcano, PNG. Volcanic Cone Collapses and Tsunami: Issues for Emergency Management in the Southwest Pacific Region. Geological Survey of Papua New Guinea and Australian Geological Survey Organisation, 1998.

Kruger, J. 2005. SOPAC/EU EDF8 Marine Survey Plan for Solomon Islands. SOPAC Report, unpublished.

Kruger, J., & Sharma, S., 2007. (in prep) Bathymetry of Solomon Islands. EU-SOPAC Report.

McAdoo, B.G., Kruger, J.C., Jackson, K.L., Moore, A.L., Rafiau, W.B. & Tiano, B. 2007. Solomon Islands Country Mission and Technical Advisory Report: Geologic Impacts of the 2nd April 2007 earthquake and tsunami on the islands and marine environment of the Western Province. EU-SOPAC Project Report 90. SOPAC Secretariat, Suva. 43 pages.

Marks, K.M., & Smith W. H. F. 2006. An evaluation of publicly available global bathymetry grids. Marine Geophysical Researches.

NGCD, 2007. NOAA/WDC Historical Tsunami Database http://www.ngdc.noaa.gov/seg/hazard/tsu_db.shtml

PDC. 2005. Tsunami Awareness Kit (Solomon Islands) http://www.pdc.org/PDCNewsWebArticles/2005TAK/index.html

Pearce, H., 2006. ATAS/AusTWC Decision Processes, NMOC, ABoM.

Pearce, H., 2007. (a) Inventory of Available Geospatial Data and Options for Tsunami Inundation & Risk Modelling, Tonga. SOPAC Miscellaneous Report MR651.

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Pearce, H. 2007. (b) Inventory of Available Geospatial Data and Options for Tsunami Inundation & Risk Modelling, Niue. SOPAC Miscellaneous Report MR652.

Pearce, H. 2007. (c) Inventory of Geospatial Data and Options for Tsunami Inundation & Risk Modelling, Kiribati. SOPAC Miscellaneous Report MR653.

Pearce, H. 2008. (in press) Inventory of Geospatial Data and Options for Tsunami Inundation & Risk Modelling, Fiji Islands. SOPAC Miscellaneous Report MR655.

Pugh, D. 2004. Changing Sea Levels, Effects of Tides, Weather and Climate.

Smith, W. & Sandwell, D. 1997. Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept., 1997.

SPSLCMP Pacific Country Report, June 2005. Sea Level & Climate: Their Present State Solomon Islands.

SPSLCMP Strategic Review Report (in prep. June 2007). South Pacific Sea level & Climate Monitoring Project , Phase IV.

Thomas, C., Burbidge, D., & Cummins, P. 2007. A Preliminary Study into the Tsunami Hazard faced by Southwest Pacific Nations, Risk and Impact Analysis Group, Geoscience Australia.

Tomita, T., Arikawa, T., Tatasumi, D., Honda, K., Higashino, H, Watanabe, K, and Takahashi, S. 2007 (in prep) Preliminary Report on Field Survey of Solomon Islands Earthquake in April 2007.

UNESCO ITIC, 2006. Tsunami Glossary http://ioc3.unesco.org/itic/files/tsunami_glossary.pdf

USGS 2007. United Stated Geological Survey web site, http://earthquake.usgs.gov/

Warne, J. 2007. Australian Tsunami Warning System Sea Level Observation System, ASLOS Network Design, Australian Bureau of Meteorology, (ABoM).

Wikipedia 2007. Tides, http://en.wikipedia.org/wiki/Tide

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APPENDIX 1

Datum and Definitions

1 Datum and Geodetic Levels at Honiara, Solomon Islands

Figure A1-1: Datum for Honiara, Solomon Islands (SPSLCMP Country Report, 2005).

Mean Sea Level (MSL) in Figure A1-1 is the average recorded level over an extended period of time. MSL at Honiara is 0.6905 metres above the SEAFRAME datum (LAT).

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2 Topographic Dataset Issues for PICs

SOPAC is the regional agency with the technical capacity and tools to collect high quality bathymetric data and also supports PICs in the collection of spot land elevation data. However, SOPAC does not have the tools to support rapid collection of topographic information over broad scale areas. Such work is increasingly being undertaken remotely using tools which can measure large areas accurately and quickly, such as aircraft mounted LIDAR (Light Detection and Ranging – a remote sensing system used to collect topographic data over large areas quickly and accurately). There is a distinct possibility that the issue of inadequate topographic data in many PICs and the limiting effect this may have on tsunami inundation modelling may require consideration of such approaches to topographic data collection.

Figure A1-2: Schematic of an aircraft mounted LIDAR system. Such systems are potentially capable of surveying shallow sub-tidal waters (too shallow for ship-borne bathymetry), inter-tidal zones, and topography (www.csc.noaa.gov/products.htm).

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3 Definitions and Acronyms

Figure A1-3: Datum

HAT (highest astronomical tide) LAT (lowest astronomical tide) These are the highest and lowest levels which can be predicted to occur under average MHHW (mean higher high water). The height of MHHW is the mean of the higher of the two daily high waters over a long period of time. When only one high water occurs on a day, this is taken as the higher high water.

Meteorological effects on tides Meteorological conditions which differ from the average will cause corresponding differences between the predicted and the actual tide. Variations in tidal heights are mainly caused by strong or prolonged winds and by unusually high or low barometric pressure.

Tidal predictions are computed for average barometric pressure. Low pressure systems tend to raise sea levels and high pressure systems tend to lower them. The water does not, however, adjust itself immediately to a change of pressure. It responds, rather, to the average change in pressure over a considerable area.

The effect of wind on sea level and therefore on tidal heights and times is variable and depends on the topography of the area in question. In general, it can be said that wind will raise the sea level in the direction towards which it is blowing. A strong wind blowing straight onshore will "pile up" the water and cause high waters to be higher than predicted, while winds blowing off the land will have the reverse effect.

MSL (mean sea level) The average level of the sea over a long period or the average level which would exist in the absence of tides.

Storm surge (http://en.wikipedia.org/wiki/Storm_surge) A storm surge is an offshore rise of water associated with a low pressure weather system, typically a tropical cyclone. Storm surge is caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea level. Low pressure at the center of a weather system also has a small secondary effect, as can

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the bathymetry of the body of water. It is this combined effect of low pressure and persistent wind over a shallow water body which is the most common cause of storm surge flooding problems. The term "storm surge" in casual (non-scientific) use is storm tide; that is, it refers to the rise of water associated with the storm, plus tide, wave run-up, and freshwater flooding. When referencing storm surge height, it is important to clarify the usage, as well as the reference point. NHC tropical storm reports reference storm surge as water height above normal astronomical tide level, and storm tide as water height above mean sea level.

In areas where there is a significant difference between low tide and high tide, storm surges are particularly damaging when they occur at the time of a high tide. In these cases, this increases the difficulty of predicting the magnitude of a storm surge since it requires weather forecasts to be accurate to within a few hours. The most extreme storm surge events occur as a result of extreme weather systems, such as tropical cyclones. Factors that determine the surge heights for landfalling tropical cyclones include the speed, intensity, size of the radius of maximum winds (RMW), radius of the wind fields, angle of the track relative to the coastline, the physical characteristics of the coastline and the bathymetry of the water offshore.

Figure A1-4: Storm surge (http://en.wikipedia.org/wiki/Storm_surge)

Sieches (Pugh 2004) Tide gauge records, particularly those from islands and places linked to oceans by narrow continental shelfs, often show high-frequency oscillations superimposed on the normal tidal changes of sea level. These oscillations, called seiches, are due to local resonant oscillations of the harbours and coastal areas. The period depends on the horizontal dimensions and depth of water in the harbour. There are a number of triggers for seiching such as gravity waves, winds, atmospheric pressure disturbances and seismic activity. When the energy for sieching comes from external wave sources e.g. a tsunami, the size of the entrance to an oscillating basin is critical.

Shoaling As a tsunami leaves the deep water of the open-ocean and travels into the shallower water near the coast, it transforms. A tsunami travels at a speed that is related to the water depth - hence, as the water depth decreases, the tsunami slows. The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami's speed diminishes, its height grows. This is called shoaling. Because of this shoaling effect, a tsunami that is unnoticeable at sea, may grow to be several metres or more in height near the coast.

The increase of the tsunami's wave height as it enters shallow water is given by:

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where hs and hd are wave heights in shallow and deep water and Hs and Hd are the depths of the shallow and deep water. So a tsunami with a height of 1 m in the open ocean where the water depth is 4000m would have a wave height of 4 to 5 m in water of depth 10 m.

Just like other water waves, tsunami begin to lose energy as they rush onshore - part of the wave energy is reflected offshore [and in the case of an atoll, around the island], while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence. Despite these losses, tsunami can still reach the coast with tremendous amounts of energy. Depending on whether the first part of the tsunami to reach the shore is a crest or a trough, it may appear as a rapidly rising or falling tide. Local bathymetry may also cause the tsunami to appear as a series of breaking waves.

Tsunami A tsunami is a series of ocean waves with very long wave lengths (typically hundreds of kilometres) caused by large-scale disturbances of the ocean, such as:

• earthquakes

• landslide

• volcanic eruptions

• explosions

• meteorites

These disturbances can either be from below (e.g. underwater earthquakes with large vertical displacements, submarine landslides) or from above (e.g. meteorite impacts).

Tsunami is a Japanese word with the English translation: "harbour wave". In the past, tsunami have been referred to as "tidal waves" or "seismic sea waves". The term "tidal wave" is misleading; even though a tsunami's impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunami are unrelated to the tides. (Tides result from the gravitational influences of the moon, sun, and planets.) The term "seismic sea wave" is also misleading. "Seismic" implies an earthquake-related generation mechanism, but a tsunami can also be caused by a non-seismic event, such as a landslide or meteorite impact.

Tsunami are also often confused with storm surges, even though they are quite different phenomena. A storm surge is a rapid rise in coastal sea level caused by a significant meteorological event - these are often associated with tropical cyclones.

Tsunami Travel Times Tsunami can have wavelengths ranging from 10 to 500 km and wave periods of up to an hour. As a result of their long wavelengths, tsunami act as shallow-water waves. A wave becomes a shallow-water wave when the wavelength is very large compared to the water depth. Shallow-water waves move at a speed, c, that is dependent upon the water depth and is given by the formula:

where g is the acceleration due to gravity (= 9.8 m/s2) and H is the depth of water (m).

As the travel times are dependant on depth of the water [H] rather than magnitude of the earthquake, scenario based travel times to any location can be pre-computed for any earthquake tsunami source.

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In the deep ocean, the typical water depth is around 4000 m, so a tsunami will therefore travel at around 200 m/s, or more than 700 km/hr.

For tsunami that are generated by underwater earthquakes, the amplitude (i.e.wave height) of the tsunami is determined by the amount by which the sea-floor is displaced. Similarly, the wavelength and period of the tsunami are determined by the size and shape of the underwater disturbance.

As well as traveling at high speeds, tsunami can also travel large distances with limited energy losses. As the tsunami propagates across the ocean, the wave crests can undergo refraction (bending), which is caused by segments of the wave moving at different speeds as the water depth along the wave crest varies.

Types of waves (http://amath.colorado.edu/courses/4380/All/ii43.pdf) There are a number of types of wave with a range of causes, physical mechanisms, periods, velocity and regions of influence affecting the oceans affecting the oceans and therefore the tide gauge. These are shown in Table A1-1.

A1-1: A number of wave types that can be found in lakes and oceans.

Tidal heights The height of the tide, in metres, is reckoned from the port datum (lowest astronomical tide (LAT) datum).

Tidal range variation: springs and neaps (http://en.wikipedia.org/wiki/Tide) The semidiurnal tidal range (the difference in height between high and low tides over about a half day) varies in a two-week or fortnightly cycle. Around new and full moon when the Sun, Moon and Earth form a line the tidal forces due to the Sun reinforce those of the Moon. The tide's range is then maximum: this is called the spring tide, or just springs and is derived not from the season of spring but rather from the verb meaning "to jump" or "to leap up". When the Moon is at first quarter or third quarter, the Sun and Moon are separated by 90° when viewed from the earth, and the forces due to the Sun partially cancel those of the Moon. At these points in the lunar cycle, the tide's range is minimum: this is called the neap tide, or neaps. Spring tides result in high waters that are higher than average, low waters that are lower than average, slack water time that is shorter than average and stronger tidal currents than average. Neaps result in less extreme tidal conditions. There is about a seven day interval between springs and neaps.

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The changing distance of the Moon from the Earth also affects tide heights. When the Moon is at perigee the range is increased and when it is at apogee the range is reduced. Every 7½ lunations, perigee coincides with either a new or full moon causing perigean tides with the largest tidal range. If a storm [or tsunami] happens to be moving onshore at this time, the consequences (in the form of property damage, etc.) can be especially severe.

Tsunami run-up (http://walrus.wr.usgs.gov/tsunami/basics.html). As the tsunami wave travels from the deep-water, continental slope region to the near- shore region, tsunami run-up occurs. Run-up is a measurement of the height of the water onshore observed above a reference sea level. Contrary to many artistic images of tsunami, most tsunami do not result in giant breaking waves (like normal surf waves at the beach that curl over as they approach shore). Rather, they come in much like very strong and very fast tides (i.e., a rapid, local rise in sea level). Much of the damage inflicted by tsunami is caused by strong currents and floating debris. The small number of tsunami that do break often form vertical walls of turbulent water called bores. Tsunami will often travel much farther inland than normal waves.

At a gauge reference sea level is the predicted tide height. Without a gauge it is often the MHW mark or MSL.

Figure A1-5: Definitions of inundation and run-up height (Tomita et al. 2007).

Volcanic sources of tsunami Tsunami can be generated from other processes such as volcanic eruption, volcanic collapse and submarine landslide. The latter are often triggered by earthquakes and are commonly attributed to the earthquake. Steep sloped bathymetry on volcanic and other islands and submarine volcanoes may have the potential to slump or collapse and depending of the size of such collapses these events may cause local tsunami if debris is dumped into the sea.

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Figure A1-6: Tsunami generation process from a volcanic collapse (IAVCEI Workshop on Ulawun Decade Volcano, 1998).

Avalanche amphitheatre

Debris avalanche deposit

24/09/414

Figure A1-7: Where debris collapses from an existing avalanche amphitheatre into the sea, it can generate a local tsunami (IAVCEI Workshop on Ulawun Decade Volcano, 1998).

Wave length

The mean horizontal distance between successive crests (or troughs) of a wave pattern.

Wave period

The average time interval between passages of successive crests (or troughs) of waves.

Wave height

Generally taken as the height difference between the wave crest and the preceding trough.

Wave amplitude Generally taken as the height above mean of wave, approximately half wave height.

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More information can be found at the following web sites:

• General information International Tsunami Information Center Welcome to tsunami! Tsunami database (U.S. National Geophysical Data Center [NGDC])

• Tsunami warning centres and hazard mitigation International Coordination Group for the Tsunami Warning System in the Pacific Pacific Tsunami Warning Center West Coast and Alaska Tsunami Warning Center U.S. National Tsunami Hazard Mitigation Program

• Earthquake information Geoscience Australia U.S. National Earthquake Information Centre European-Mediterranean Seismological Centre

• The Indian Ocean tsunami of Dec. 26th 2004 Scientific Background (from Columbia University)

• Tsunami research Tsunami Research Center (University of Southern California) Tsunami Research Program (Pacific Marine Environmental Laboratory)

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APPENDIX 2

Historical Tsunami Events Affecting Solomon Islands

a. Previous Tsunami that have been recorded in Solomon Islands

Extracts from National Geophysical Data Centre (NGDC), Tsunami Inundation Database show the highest recorded tsunami events in the Solomon Islands were: 10.5 m at Beaufort Bay, on the south west coast of Guadalcanal in 1939, 10 m at Ghizo in 2007 and 9 m at San Cristobal Island in 1931. These were all from near by Solomons Trench sources. One event was recorded from a regional source in Vanuatu on the New Hebrides Trench in 2007. There are very few recorded run-ups from distant (ocean-wide) sources. Those recorded were from Russia in 1952 and 2006 with both less than 1 m.

Table A2-1 (a) & (b): Extracts from National Geophysical Data Centre (NGDC), Tsunami Inundation Database (a) Source generating run-up event (b) location of run-up.

(a)

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(b)

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2 Recent PTWC Warnings

(i) Solomon Islands 2 April 2007 Tsunami

Figure A2-1: USGS Poster of Solomon Islands 2 April 2007 Earthquake (http://earthquake.usgs.gov).

Figure A2-2: Travel times map and model scenario for Solomon’s tsunami 2 April 2007.

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The Solomons Trench earthquake of 2 April 2007 is described in the USGS poster at Figure A2-1. The model scenario and forecast travel times for the tsunami are shown at Figure A2-2. The Solomon Islands warning points used by the PTWC are at Table A2-2 and the PTWC Warnings for this event are below. During the PTWC expanding warning/watch phase, any of the locations below is within three hours (warning) or six hours (watch) travel time for the predicted expanding tsunami, all the Solomon Islands will be included in the warning/watch process. Travel times are then provided for all Solomon Islands locations whether in warning or watch range. Note that the initial estimate of magnitude was 7.8 and a regional (see A2 3(i)) warning covering 1000 km/three hours travel time was issued. In the second warning the estimate of magnitude was increased to 8.1 and an expanding warning/watch phase was initiated for a potential ocean-wide tsunami. The forecast the travel time to Honiara from source was forty minutes from the earthquake, twenty-five (25) minutes after first PTWC bulletin issued.

Table A2-2: Solomon Islands warning locations used by PTWC.

MUNDA 8.4S 157.2E Rendova Island FALAMAE 7.4S 155.6E Mono Island PANGGOE 6.9S 157.2E Choiseul Island HONIARA 9.3S 160.0E Guadalcanal GHATERE 7.8S 159.2E Santa Isabel Island AUKI 8.8S 160.6E Malaita Island KIRAKIRA 10.4S 161.9E San Cristobal Island

Figure A2-3: Locations of PTWC warning reference points in Solomon Islands based on Table A2-2.

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Example 1: PTWC Bulletin No 1

TSUNAMI BULLETIN NUMBER 001

PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 2055Z 01 APR 2007

THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA.

... A TSUNAMI WARNING IS IN EFFECT ...

A TSUNAMI WARNING IS IN EFFECT FOR

SOLOMON IS. / PAPUA NEW GUINEA

FOR ALL OTHER PACIFIC AREAS, THIS MESSAGE IS AN ADVISORY ONLY.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 2040Z 01 APR 2007 COORDINATES - 8.6 SOUTH 157.2 EAST LOCATION - SOLOMON ISLANDS MAGNITUDE - 7.8

EVALUATION

IT IS NOT KNOWN THAT A TSUNAMI WAS GENERATED. THIS WARNING IS BASED ONLY ON THE EARTHQUAKE EVALUATION. AN EARTHQUAKE OF THIS SIZE HAS THE POTENTIAL TO GENERATE A DESTRUCTIVE TSUNAMI THAT CAN STRIKE COASTLINES IN THE REGION NEAR THE EPICENTER WITHIN MINUTES TO HOURS. AUTHORITIES IN THE REGION SHOULD TAKE APPROPRIATE ACTION IN RESPONSE TO THIS POSSIBILITY. THIS CENTER WILL MONITOR SEA LEVEL GAUGES NEAREST THE REGION AND REPORT IF ANY TSUNAMI WAVE ACTIVITY IS OBSERVED. THE WARNING WILL NOT EXPAND TO OTHER AREAS OF THE PACIFIC UNLESS ADDITIONAL DATA ARE RECEIVED TO WARRANT SUCH AN EXPANSION.

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES. ACTUAL ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. THE TIME BETWEEN SUCCESSIVE TSUNAMI WAVES CAN BE FIVE MINUTES TO ONE HOUR.

LOCATION COORDINATES ARRIVAL TIME ------SOLOMON IS. MUNDA 8.4S 157.2E 2039Z 01 APR FALAMAE 7.4S 155.6E 2059Z 01 APR PANGGOE 7.0S 157.5E 2108Z 01 APR GHATERE 7.5S 159.0E 2117Z 01 APR HONIARA 9.0S 160.0E 2120Z 01 APR AUKI 8.8S 160.6E 2130Z 01 APR KIRAKIRA 10.0S 162.0E 2136Z 01 APR PAPUA NEW GUINE AMUN 6.0S 154.7E 2116Z 01 APR KIETA 6.1S 155.6E 2123Z 01 APR RABAUL 4.2S 152.3E 2145Z 01 APR LAE 6.8S 147.0E 2214Z 01 APR KAVIENG 2.5S 150.7E 2216Z 01 APR MADANG 5.2S 145.8E 2241Z 01 APR MANUS IS. 2.0S 147.5E 2250Z 01 APR PORT MORESBY 9.3S 146.9E 2252Z 01 APR WEWAK 3.5S 144.0E 2319Z 01 APR VANIMO 2.6S 141.3E 2346Z 01 APR

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT. THE TSUNAMI WARNING WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.

THE JAPAN METEOROLOGICAL AGENCY MAY ALSO ISSUE TSUNAMI MESSAGES FOR THIS EVENT TO COUNTRIES IN THE NORTHWEST PACIFIC AND SOUTH CHINA SEA REGION. IN CASE OF CONFLICTING INFORMATION... THE MORE CONSERVATIVE INFORMATION SHOULD BE USED FOR SAFETY.

THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE BULLETINS FOR ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA.

[SOPAC Miscellaneous Report 654 – Pearce] [49]

TSUNAMI BULLETIN NUMBER 002

PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 2132Z 01 APR 2007

THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA.

... A TSUNAMI WARNING AND WATCH ARE IN EFFECT ...

A TSUNAMI WARNING IS IN EFFECT FOR

SOLOMON IS. / PAPUA NEW GUINEA / VANUATU / NAURU / CHUUK / NEW CALEDONIA / POHNPEI / KOSRAE / AUSTRALIA / INDONESIA / TUVALU / KIRIBATI / MARSHALL IS.

A TSUNAMI WATCH IS IN EFFECT FOR

GUAM / FIJI / N. MARIANAS / YAP / HOWLAND-BAKER / WALLIS-FUTUNA / BELAU / TOKELAU / KERMADEC IS / SAMOA / NEW ZEALAND / MARCUS IS. / WAKE IS. / AMERICAN SAMOA / TONGA / NIUE / COOK ISLANDS / PHILIPPINES / JARVIS IS. / PALMYRA IS. / JOHNSTON IS. / JAPAN

FOR ALL OTHER PACIFIC AREAS, THIS MESSAGE IS AN ADVISORY ONLY.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 2040Z 01 APR 2007 COORDINATES - 8.6 SOUTH 157.2 EAST LOCATION - SOLOMON ISLANDS MAGNITUDE - 8.1

EVALUATION

IT IS NOT KNOWN THAT A TSUNAMI WAS GENERATED. THIS WARNING IS BASED ONLY ON THE EARTHQUAKE EVALUATION. AN EARTHQUAKE OF THIS SIZE HAS THE POTENTIAL TO GENERATE A DESTRUCTIVE TSUNAMI THAT CAN STRIKE COASTLINES NEAR THE EPICENTER WITHIN MINUTES AND MORE DISTANT COASTLINES WITHIN HOURS. AUTHORITIES SHOULD TAKE APPROPRIATE ACTION IN RESPONSE TO THIS POSSIBILITY. THIS CENTER WILL MONITOR SEA LEVEL DATA FROM GAUGES NEAR THE EARTHQUAKE TO DETERMINE IF A TSUNAMI WAS GENERATED AND ESTIMATE THE SEVERITY OF THE THREAT.

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES. ACTUAL ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. THE TIME BETWEEN SUCCESSIVE TSUNAMI WAVES CAN BE FIVE MINUTES TO ONE HOUR.

LOCATION COORDINATES ARRIVAL TIME ------SOLOMON IS. MUNDA 8.4S 157.2E 2039Z 01 APR FALAMAE 7.4S 155.6E 2103Z 01 APR PANGGOE 6.9S 157.2E 2120Z 01 APR HONIARA 9.3S 160.0E 2121Z 01 APR GHATERE 7.8S 159.2E 2122Z 01 APR AUKI 8.8S 160.6E 2134Z 01 APR KIRAKIRA 10.4S 161.9E 2140Z 01 APR PAPUA NEW GUINE AMUN 6.0S 154.7E 2124Z 01 APR KIETA 6.1S 155.6E 2133Z 01 APR RABAUL 4.2S 152.3E 2145Z 01 APR LAE 6.8S 147.0E 2218Z 01 APR KAVIENG 2.5S 150.7E 2223Z 01 APR MADANG 5.2S 146.0E 2241Z 01 APR PORT MORESBY 9.5S 147.0E 2254Z 01 APR MANUS IS. 2.0S 147.5E 2259Z 01 APR WEWAK 3.5S 143.6E 2325Z 01 APR VANIMO 2.6S 141.3E 2350Z 01 APR VANUATU ESPERITU SANTO 15.1S 167.3E 2236Z 01 APR ANATOM IS. 20.2S 169.9E 2322Z 01 APR NAURU NAURU 0.5S 166.9E 2311Z 01 APR CHUUK CHUUK IS. 7.4N 151.8E 2329Z 01 APR NEW CALEDONIA NOUMEA 22.3S 166.5E 2338Z 01 APR POHNPEI POHNPEI IS. 7.0N 158.2E 2345Z 01 APR KOSRAE KOSRAE IS. 5.5N 163.0E 2345Z 01 APR AUSTRALIA CAIRNS 16.7S 145.8E 2349Z 01 APR BRISBANE 27.2S 153.3E 0033Z 02 APR SYDNEY 33.9S 151.4E 0114Z 02 APR GLADSTONE 23.8S 151.4E 0139Z 02 APR

[SOPAC Miscellaneous Report 654 – Pearce] [50]

MACKAY 21.1S 149.3E 0144Z 02 APR HOBART 43.3S 147.6E 0245Z 02 APR INDONESIA JAYAPURA 2.4S 140.8E 2354Z 01 APR WARSA 0.6S 135.8E 0037Z 02 APR MANOKWARI 0.8S 134.2E 0056Z 02 APR

PATANI 0.4N 128.8E 0158Z 02 APR GEME 4.8N 126.8E 0202Z 02 APR MANADO 1.5N 124.8E 0242Z 02 APR TARAKAN 3.3N 117.6E 0400Z 02 APR SINGKAWANG 1.0N 108.8E 1240Z 02 APR PANGKALPINANG 2.0S 106.2E 1547Z 02 APR TUVALU FUNAFUTI IS. 7.9S 178.5E 2359Z 01 APR KIRIBATI TARAWA IS. 1.5N 173.0E 0007Z 02 APR KANTON IS. 2.8S 171.7W 0121Z 02 APR CHRISTMAS IS. 2.0N 157.5W 0325Z 02 APR MALDEN IS. 3.9S 154.9W 0336Z 02 APR FLINT IS. 11.4S 151.8W 0408Z 02 APR MARSHALL IS. KWAJALEIN 8.7N 167.7E 0022Z 02 APR MAJURO 7.1N 171.4E 0028Z 02 APR ENIWETOK 11.4N 162.3E 0037Z 02 APR GUAM GUAM 13.4N 144.7E 0035Z 02 APR FIJI SUVA 18.1S 178.4E 0038Z 02 APR N. MARIANAS SAIPAN 15.3N 145.8E 0041Z 02 APR YAP YAP IS. 9.5N 138.1E 0048Z 02 APR HOWLAND-BAKER HOWLAND IS. 0.6N 176.6W 0057Z 02 APR WALLIS-FUTUNA WALLIS IS. 13.2S 176.2W 0100Z 02 APR BELAU MALAKAL 7.3N 134.5E 0103Z 02 APR TOKELAU NUKUNONU IS. 9.2S 171.8W 0119Z 02 APR KERMADEC IS RAOUL IS. 29.2S 177.9W 0131Z 02 APR SAMOA APIA 13.8S 171.8W 0135Z 02 APR NEW ZEALAND NORTH CAPE 34.4S 173.3E 0138Z 02 APR EAST CAPE 37.5S 178.5E 0214Z 02 APR AUCKLAND(W) 37.1S 174.2E 0238Z 02 APR GISBORNE 38.7S 178.0E 0247Z 02 APR MILFORD SOUND 44.5S 167.8E 0249Z 02 APR NEW PLYMOUTH 39.1S 174.1E 0310Z 02 APR NAPIER 39.5S 176.9E 0316Z 02 APR WESTPORT 41.8S 171.2E 0332Z 02 APR AUCKLAND(E) 36.7S 175.0E 0332Z 02 APR WELLINGTON 41.5S 174.8E 0333Z 02 APR BLUFF 46.6S 168.3E 0351Z 02 APR NELSON 41.3S 173.3E 0426Z 02 APR LYTTELTON 43.6S 172.7E 0439Z 02 APR DUNEDIN 45.9S 170.5E 0506Z 02 APR MARCUS IS. MARCUS IS. 24.3N 154.0E 0138Z 02 APR WAKE IS. WAKE IS. 19.3N 166.6E 0141Z 02 APR AMERICAN SAMOA PAGO PAGO 14.3S 170.7W 0144Z 02 APR TONGA NUKUALOFA 21.0S 175.2W 0152Z 02 APR NIUE NIUE IS. 19.0S 170.0W 0209Z 02 APR COOK ISLANDS PUKAPUKA IS. 10.8S 165.9W 0212Z 02 APR PENRYN IS. 8.9S 157.8W 0316Z 02 APR RAROTONGA 21.2S 159.8W 0324Z 02 APR PHILIPPINES DAVAO 6.8N 125.7E 0215Z 02 APR LEGASPI 13.2N 124.0E 0248Z 02 APR ZAMBOANGA 7.0N 122.2E 0256Z 02 APR PALANAN 17.1N 122.6E 0307Z 02 APR LAOAG 18.2N 120.6E 0352Z 02 APR PUERTO PRINCESA 9.8N 119.0E 0404Z 02 APR SAN FERNANDO 16.6N 120.3E 0421Z 02 APR ILOILO 10.8N 122.8E 0438Z 02 APR MANILA 14.5N 120.8E 0517Z 02 APR JARVIS IS. JARVIS IS. 0.4S 160.1W 0256Z 02 APR PALMYRA IS. PALMYRA IS. 6.3N 162.4W 0300Z 02 APR JOHNSTON IS. JOHNSTON IS. 16.7N 169.5W 0308Z 02 APR JAPAN KATSUURA 35.1N 140.3E 0312Z 02 APR OKINAWA 26.2N 128.0E 0318Z 02 APR SHIMIZU 32.8N 132.8E 0359Z 02 APR KUSHIRO 42.8N 144.2E 0410Z 02 APR HACHINOHE 40.5N 141.8E 0415Z 02 APR

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT. THE TSUNAMI WARNING AND WATCH WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.

[SOPAC Miscellaneous Report 654 – Pearce] [51]

TSUNAMI BULLETIN NUMBER 006

PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 0158Z 02 APR 2007

THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA.

NOTE: AREAS TO THE NORTH OF THE SOLOMON ISLANDS SHOULD NOT BE SIGNIFICANTLY AFFECTED

... A TSUNAMI WARNING AND WATCH ARE IN EFFECT ...

A TSUNAMI WARNING IS IN EFFECT FOR

SOLOMON IS. / PAPUA NEW GUINEA / VANUATU / NEW CALEDONIA / NORTHEASTERN AUSTRALIA / TUVALU / KIRIBATI / FIJI / KERMADEC IS / NEW ZEALAND

FOR ALL OTHER PACIFIC AREAS, THIS MESSAGE IS AN ADVISORY ONLY.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 2040Z 01 APR 2007 COORDINATES - 8.6 SOUTH 157.2 EAST LOCATION - SOLOMON ISLANDS MAGNITUDE - 8.1

MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY

GAUGE LOCATION LAT LON TIME AMPL PER ------MANUS PG 2.0S 147.4E 0040Z 0.09M = 0.3FT 40MIN VANUATU VU 17.8S 168.3E 0114Z 0.14M = 0.5FT 28MIN HONIARA SB 9.4S 160.0E 2308Z 0.20M = 0.6FT 62MIN

LAT - LATITUDE (N=NORTH, S=SOUTH) LON - LONGITUDE (E=EAST, W=WEST) TIME - TIME OF THE MEASUREMENT (Z = UTC = GREENWICH TIME) AMPL - TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL. IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. VALUES ARE GIVEN IN BOTH METERS (M) AND FEET (FT). PER - PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT.

NOTE: PTWC HAS RECEIVED REPORTS OF TSUNAMI RELATED FATALITIES IN SOUTHEAST PAPUA NEW GUINEA AND THE SOLOMON ISLANDS.

EVALUATION

SEA LEVEL READINGS INDICATE A TSUNAMI WAS GENERATED. IT MAY HAVE BEEN DESTRUCTIVE ALONG COASTS NEAR THE EARTHQUAKE EPICENTER AND COULD ALSO BE A THREAT TO MORE DISTANT COASTS. AUTHORITIES SHOULD TAKE APPROPRIATE ACTION IN RESPONSE TO THIS POSSIBILITY. THIS CENTER WILL CONTINUE TO MONITOR SEA LEVEL DATA TO DETERMINE THE EXTENT AND SEVERITY OF THE THREAT.

FOR ALL AREAS - WHEN NO MAJOR WAVES ARE OBSERVED FOR TWO HOURS AFTER THE ESTIMATED TIME OF ARRIVAL OR DAMAGING WAVES HAVE NOT OCCURRED FOR AT LEAST TWO HOURS THEN LOCAL AUTHORITIES CAN ASSUME THE THREAT IS PASSED. DANGER TO BOATS AND COASTAL STRUCTURES CAN CONTINUE FOR SEVERAL HOURS DUE TO RAPID CURRENTS. AS LOCAL CONDITIONS CAN CAUSE A WIDE VARIATION IN TSUNAMI WAVE ACTION THE ALL CLEAR DETERMINATION MUST BE MADE BY LOCAL AUTHORITIES.

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES. ACTUAL ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. THE TIME BETWEEN SUCCESSIVE TSUNAMI WAVES CAN BE FIVE MINUTES TO ONE HOUR.

[SOPAC Miscellaneous Report 654 – Pearce] [52]

KIRAKIRA 10.4S 161.9E 2140Z 01 APR PAPUA NEW GUINE AMUN 6.0S 154.7E 2124Z 01 APR KIETA 6.1S 155.6E 2133Z 01 APR RABAUL 4.2S 152.3E 2145Z 01 APR LAE 6.8S 147.0E 2218Z 01 APR KAVIENG 2.5S 150.7E 2223Z 01 APR MADANG 5.2S 146.0E 2241Z 01 APR PORT MORESBY 9.5S 147.0E 2254Z 01 APR MANUS IS. 2.0S 147.5E 2259Z 01 APR WEWAK 3.5S 143.6E 2325Z 01 APR VANIMO 2.6S 141.3E 2350Z 01 APR VANUATU ESPERITU SANTO 15.1S 167.3E 2236Z 01 APR ANATOM IS. 20.2S 169.9E 2322Z 01 APR NEW CALEDONIA NOUMEA 22.3S 166.5E 2338Z 01 APR AUSTRALIA CAIRNS 16.7S 145.8E 2349Z 01 APR BRISBANE 27.2S 153.3E 0033Z 02 APR SYDNEY 33.9S 151.4E 0114Z 02 APR GLADSTONE 23.8S 151.4E 0139Z 02 APR MACKAY 21.1S 149.3E 0144Z 02 APR HOBART 43.3S 147.6E 0245Z 02 APR TUVALU FUNAFUTI IS. 7.9S 178.5E 2359Z 01 APR KIRIBATI TARAWA IS. 1.5N 173.0E 0007Z 02 APR KANTON IS. 2.8S 171.7W 0121Z 02 APR CHRISTMAS IS. 2.0N 157.5W 0325Z 02 APR MALDEN IS. 3.9S 154.9W 0336Z 02 APR FLINT IS. 11.4S 151.8W 0408Z 02 APR FIJI SUVA 18.1S 178.4E 0038Z 02 APR KERMADEC IS RAOUL IS. 29.2S 177.9W 0131Z 02 APR NEW ZEALAND NORTH CAPE 34.4S 173.3E 0138Z 02 APR EAST CAPE 37.5S 178.5E 0214Z 02 APR AUCKLAND(W) 37.1S 174.2E 0238Z 02 APR GISBORNE 38.7S 178.0E 0247Z 02 APR MILFORD SOUND 44.5S 167.8E 0249Z 02 APR NEW PLYMOUTH 39.1S 174.1E 0310Z 02 APR NAPIER 39.5S 176.9E 0316Z 02 APR WESTPORT 41.8S 171.2E 0332Z 02 APR AUCKLAND(E) 36.7S 175.0E 0332Z 02 APR WELLINGTON 41.5S 174.8E 0333Z 02 APR BLUFF 46.6S 168.3E 0351Z 02 APR NELSON 41.3S 173.3E 0426Z 02 APR LYTTELTON 43.6S 172.7E 0439Z 02 APR DUNEDIN 45.9S 170.5E 0506Z 02 APR

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT. THE TSUNAMI WARNING AND WATCH WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE.

TSUNAMI BULLETIN NUMBER 004 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 0013Z 02 APR 2007

THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA.

NOTE: AREAS TO THE NORTH OF THE SOLOMONS SHOULD NOT BE SIGNIFICANTLY AFFECTED.

... A TSUNAMI WARNING AND WATCH REMAINS IN EFFECT ...

A TSUNAMI WARNING IS IN EFFECT FOR

SOLOMON IS. / PAPUA NEW GUINEA / VANUATU / NEW CALEDONIA / AUSTRALIA / TUVALU / KIRIBATI / FIJI

A TSUNAMI WATCH IS IN EFFECT FOR

KERMADEC / NEW ZEALAND

FOR ALL OTHER PACIFIC AREAS, THIS MESSAGE IS AN ADVISORY ONLY.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 2040Z 01 APR 2007 COORDINATES - 8.6 SOUTH 157.2 EAST LOCATION - SOLOMON ISLANDS MAGNITUDE - 8.1

[SOPAC Miscellaneous Report 654 – Pearce] [53]

MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY

GAUGE LOCATION LAT LON TIME AMPL PER ------HONIARA SB 9.4S 160.0E 2235Z 0.14M = 0.5FT 70MIN VANUATU VU 17.8S 168.3E 2351Z 0.11M = 0.4FT 26MIN

LAT - LATITUDE (N=NORTH, S=SOUTH) LON - LONGITUDE (E=EAST, W=WEST) TIME - TIME OF THE MEASUREMENT (Z = UTC = GREENWICH TIME) AMPL - TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL. IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. VALUES ARE GIVEN IN BOTH METERS(M) AND FEET(FT). PER - PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT.

EVALUATION

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES. ACTUAL ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. THE TIME BETWEEN SUCCESSIVE TSUNAMI WAVES CAN BE FIVE MINUTES TO ONE HOUR.

[SOPAC Miscellaneous Report 654 – Pearce] [54]

Figure A2-4: Tide gauge recordings for Solomon Islands tsunami, 2 April 2007.

Figure A2-5: Tide gauge recording for 2 April 2007 tsunami over the deep-water model scenario closest to the event.

[SOPAC Miscellaneous Report 654 – Pearce] [55]

(a)

(b)

Figure A2-6: Tide gauge recording at Honiara for 2 April 2007 tsunami (a) Tide and tsunami signal (b) tsunami signal with predicted tide removed (ABoM)

[SOPAC Miscellaneous Report 654 – Pearce] [56]

(a)

(b)

Figure A2-7: Tide gauge recording at Port Vila for 2 April 2007 tsunami (a) tide and tsunami signal (b) tsunami signal with predicted tide removed (Source: ABoM, 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [57]

(ii) September 2007 Santa Cruz Tsunami Bulletins

The Santa Cruz earthquake 7.4 Mw, 2 September 2007, was within the range 6.5-7.5 Mw and the bulletin (rather than warning) produced by the PTWC advised of the potential for a Local (see A2-3 (i)) tsunami within 100 km. The distances to Honiara and Port Villa were greater than 100 km and estimated travel times greater than one hour. The Port Vila tide gauge recorded a 4-cm amplitude (8 cm peak-to-trough).

TSUNAMI BULLETIN NUMBER 001 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 0121Z 02 SEP 2007

THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA... WASHINGTON...OREGON AND CALIFORNIA.

... TSUNAMI INFORMATION BULLETIN ...

THIS BULLETIN IS FOR INFORMATION ONLY.

THIS BULLETIN IS ISSUED AS ADVICE TO GOVERNMENT AGENCIES. ONLY NATIONAL AND LOCAL GOVERNMENT AGENCIES HAVE THE AUTHORITY TO MAKE DECISIONS REGARDING THE OFFICIAL STATE OF ALERT IN THEIR AREA AND ANY ACTIONS TO BE TAKEN IN RESPONSE.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 0105Z 02 SEP 2007 COORDINATES - 11.8 SOUTH 166.0 EAST DEPTH - SHALLOWER THAN 100 KM LOCATION - SANTA CRUZ ISLANDS MAGNITUDE - 7.4

EVALUATION

NO DESTRUCTIVE WIDESPREAD TSUNAMI THREAT EXISTS BASED ON HISTORICAL EARTHQUAKE AND TSUNAMI DATA.

HOWEVER - EARTHQUAKES OF THIS SIZE SOMETIMES GENERATE LOCAL TSUNAMI THAT CAN BE DESTRUCTIVE ALONG COASTS LOCATED WITHIN A HUNDRED KILOMETERS OF THE EARTHQUAKE EPICENTER. AUTHORITIES IN THE REGION OF THE EPICENTER SHOULD BE AWARE OF THIS POSSIBILITY AND TAKE APPROPRIATE ACTION.

THIS WILL BE THE ONLY BULLETIN ISSUED FOR THIS EVENT UNLESS ADDITIONAL INFORMATION BECOMES AVAILABLE.

THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE PRODUCTS FOR ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON...CALIFORNIA.

TSUNAMI BULLETIN NUMBER 002 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 0159Z 02 SEP 2007

THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA... WASHINGTON...OREGON AND CALIFORNIA.

... TSUNAMI INFORMATION BULLETIN ...

THIS BULLETIN IS FOR INFORMATION ONLY.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 0105Z 02 SEP 2007 COORDINATES - 11.8 SOUTH 166.0 EAST

[SOPAC Miscellaneous Report 654 – Pearce] [58]

DEPTH - SHALLOWER THAN 100 KM LOCATION - SANTA CRUZ ISLANDS MAGNITUDE - 7.3 (NOTE THIS IS REDUCED FROM 7.4)

EVALUATION

FURTHER SEISMIC ANALYSIS INDICATES THAT THIS EARTHQUAKE MAY BE THE KIND OF EARTHQUAKE THAT RUPTURES MORE SLOWLY AND HAS AN INCREASED POTENTIAL TO GENERATE TSUNAMI WAVES THAT COULD BE DAMAGING NEAR THE EPICENTER. THIS CENTER WILL CONTINUE TO MONITOR NEARBY SEA LEVEL GAUGES AND WILL REPORT ANY TSUNAMI WAVES THAT ARE OBSERVED.

THIS WILL BE THE FINAL BULLETIN ISSUED FOR THIS EVENT UNLESS ADDITIONAL INFORMATION BECOMES AVAILABLE.

THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE PRODUCTS FOR ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON...CALIFORNIA.

TSUNAMI BULLETIN NUMBER 003 PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS ISSUED AT 0426Z 02 SEP 2007

THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA... WASHINGTON...OREGON AND CALIFORNIA.

... TSUNAMI INFORMATION BULLETIN ...

THIS BULLETIN IS FOR INFORMATION ONLY.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 0105Z 02 SEP 2007 COORDINATES - 11.8 SOUTH 166.0 EAST DEPTH - 33 KM LOCATION - SANTA CRUZ ISLANDS MAGNITUDE - 7.3

MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY

GAUGE LOCATION LAT LON TIME AMPL PER ------VANUATU VU 17.8S 168.3E 0339Z 0.04M / 0.1FT 26MIN

LAT - LATITUDE (N-NORTH, S-SOUTH) LON - LONGITUDE (E-EAST, W-WEST) TIME - TIME OF THE MEASUREMENT (Z IS UTC IS GREENWICH TIME) AMPL - TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL. IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. VALUES ARE GIVEN IN BOTH METERS(M) AND FEET(FT). PER - PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT.

EVALUATION

SEA LEVEL READINGS INDICATE A TSUNAMI WAS GENERATED. IT MAY HAVE BEEN DESTRUCTIVE ALONG COASTS NEAR THE EARTHQUAKE EPICENTER. FOR THOSE AREAS - WHEN NO MAJOR WAVES ARE OBSERVED FOR TWO HOURS AFTER THE ESTIMATED TIME OF ARRIVAL OR DAMAGING WAVES HAVE NOT OCCURRED FOR AT LEAST TWO HOURS THEN LOCAL AUTHORITIES CAN ASSUME THE THREAT IS PASSED. DANGER TO BOATS AND COASTAL STRUCTURES CAN CONTINUE FOR SEVERAL HOURS DUE TO THE CONTINUING SEA LEVEL CHANGES AND RAPID CURRENTS. AS LOCAL CONDITIONS CAN CAUSE A WIDE VARIATION IN TSUNAMI WAVE ACTION THE ALL CLEAR DETERMINATION MUST BE MADE BY LOCAL AUTHORITIES.

NO TSUNAMI THREAT EXISTS FOR OTHER COASTAL AREAS IN THE PACIFIC ALTHOUGH SOME OTHER AREAS MAY EXPERIENCE SMALL NON-DESTRUCTIVE SEA LEVEL CHANGES LASTING UP TO SEVERAL HOURS.

[SOPAC Miscellaneous Report 654 – Pearce] [59]

3 Tsunami Warning Related Background

(i) Summary of JMA/PTWC causal earthquake criteria

Table A2-3: JMA and PTWC use simple criteria based on magnitude of the earthquake as a quick approximate assessment of an earthquakes potential to generate Local, Regional and Ocean-wide Tsunami (Pearce, 2006).

Magnitude* (Mw) PTWC & JMA Bulletin/Warning if less than 100 km deep * Mw and depth may change in first hour ** Amplitude for Destructive Tsunami > 0 .5 m Potential for a Locally destructive** tsunami within 1 hr 6.5 to 7.5 (100 km) Potential for a Regionally destructive** tsunami within 7.6 to 7.8 3 hr (1000 km )

7.9 and above Potential for an Ocean Wide destructive ** tsunami

Table A2-3 provides a summary of the simple criteria, based on magnitude, from PTWC/JMA and ATAS, used as a first approximation of an earthquake’s potential to produce a local, regional or ocean-wide tsunami. Maximum tsunami wave height is more directly proportional to the vertical displacement of the rupture; however as magnitude can generally be determined within 10-15 minutes, it is used in the warning process to provide a quick approximation. The vertical displacement takes considerably longer and is more difficult to estimate.

If an earthquake is deeper than 100 km in the Earth’s crust, no tsunami will be generated. An event in the range 6.5 to 7.5 Mw could produce a locally destructive tsunami affecting an area within 100 km or one hour’s travel time. An event between 7.6 to 7.9 Mw could produce a regionally destructive tsunami affecting an area within 1000 km or three hours travel time. Anything 7.9 Mw and above has the potential to produce an ocean-wide destructive tsunami. The PTWC and JMA also use the criteria, equal to or greater than 0.5 m amplitude as the definition of a destructive tsunami.

The PTWC Bulletins are issued as advice to government agencies. Only national and local government agencies have the authority to make decisions regarding the official state of alert in their area and any actions to be taken in response. All PTWC warnings and travel-times are in UTC (equivalent Z and GMT).

It is a national responsibility to provide public information; e.g. expected time of arrival in local and UTC time, recorded heights, the need to wait approximately two to three hours from expected or actual time of arrival for all clear.

[SOPAC Miscellaneous Report 654 – Pearce] [60]

(ii) Tsunami hazard sources

The source of historical earthquake generated tsunami events around the Pacific is shown in Figure A2-8; and Figure A2-9 shows the time it would take a tsunami from any location to reach Honiara (i.e. inverse Tsunami Travel Time).

Figure A2-8: Historical tsunami events in the Pacific and Eastern Indian Ocean. Circle size indicates earthquake magnitude and colour indicates tsunami intensity (SPSLCMP Pacific Country Report, June 2005).

Figure A2-9: Inverse tsunami travel times (hours) for the Solomon Islands capital, Honiara. (SPSLCMP Pacific Country Report, June 2005).

[SOPAC Miscellaneous Report 654 – Pearce] [61]

(iii) Real-Time sea level data available for tsunami monitoring

The Solomon Island sea level monitoring gauge at Honiara was installed in 1974 by the University of Hawai’i. After the Banda Ache Tsunami in 2004, semi real-time data communications was installed by ABoM allowing access to 10-minute updates of 1 minute data.

Real-time sea level data for monitoring tsunami in the Pacific is available from other Pacific sea level monitoring gauges to all National Meteorological Agencies through the World Meteorological Organisations (WMO) global telecommunications system (GTS) network. Software is available from the IOC to decode and display this data. SOPAC is looking at a range of options for making this data and the analysis tools available to PICs.

Currently most Pacific island countries access even their own data through web services such as University of Hawai’i (Figure A2-10) and Australian Bureau of Meteorology (ABoM) (Figure A2-11 and Table A2-4).

Most of these gauges are in lagoons or harbours and readings will include a range of additional effects such as shoaling and seiching as well as other background noise, which can make it hard to distinguish a small tsunami signal. Tidal information to complement tsunami warning arrival times is available at: http://www.bom.gov.au/oceanography/tides/MAPS/pac.shtml.

NOAA Dart Buoy network data (Figure A2-12) is available in semi real-time through http://www.ndbc.noaa.gov/dart.shtml. These gauges are in deep water (about 3000 m) and are not affected by shoaling or seiching.

Unfortunately, it is not possible to locate the current type of DART buoy too close to a Trench, such as between the Solomon’ s Trench and the Solomon Islands, due to the effects of the seismic signal overpowering the tsunami wave signal. Therefore there would be little chance of confirming a tsunami has been generated by an earthquake from the Solomons Trench before it reached parts of the Solomon Islands. However the gauges on the University of Hawai’i web page are useful for early warning for the northwest sources.

Figure A2-10: Location of University of Hawai’i real-time sea level sites (http://uhslc.soest.hawaii.edu/uhslc/data.html).

[SOPAC Miscellaneous Report 654 – Pearce] [62]

Figure A2-11: Locations of Australia’s seaframe tide gauge network for the Southwest Pacific. This network is also used for tsunami monitoring (Warne 2007).

Table A2-4: List of seaframe gauges in the Pacific and update frequency available for monitoring tsunami.

The update frequency of the Pacific array is in the process of being upgraded to 10-min updates.

[SOPAC Miscellaneous Report 654 – Pearce] [63]

Figure A2-12: Locations of Deep ocean tsunami monitoring buoy network.

[SOPAC Miscellaneous Report 654 – Pearce] [64]

APPENDIX 3

Additional Modelling

1 Modelling of major tsunami for sources around the Pacific

The deep-water modelling for the 39 magnitude 9 tsunami sources around the Pacific, used in the composite in Section 4, are shown in Figure A3-1. Note that the main energy is beamed perpendicular to the trench and then channelled by bathymetry. The Solomons Trench source Figure A3-1 (31, 32, 33 & 34) are the most critical for the Solomon Islands.

1 2

3 4

5 6

[SOPAC Miscellaneous Report 654 – Pearce] [65]

7 8

9 10

11 12

14 13

[SOPAC Miscellaneous Report 654 – Pearce] [66]

16 15

18 17

19 20

22 21

[SOPAC Miscellaneous Report 654 – Pearce] [67]

23 24

25 26

27 28

29 30

[SOPAC Miscellaneous Report 654 – Pearce] [68]

31 32

33 34

36 35

38 37

[SOPAC Miscellaneous Report 654 – Pearce] [69]

Figure A3-1: Sources for 9 Mw generated tsunami around the Pacific (Thomas, personal comm. 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [70]

2 MOST scenarios for sources affecting Solomon Islands (Source: ABoM)

(i) Solomons Trench

MOST (Method of Splitting Tsunami) Model scenarios for 9.0, 8.5, 8.0 and 7.5 Mw potential events on the Solomons Trench are at Figure A3-3. For events up to 8 Mw most of the energy is contained within the Solomon Islands or focused to the southwest. Above this magnitude, by virtue of the larger rupture area (Figure A3-2), the energy is focused to the northeast.

Figure A3-2: Pink represents the area ruptured during the 2 April 2007 event. The area grey area would need to rupture to produce a Magnitude 9 generated tsunami event (Cummins 2007).

Figure A3-3: Solomons Trench most significant, with very short warning times (ABoM 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [71]

(ii) New Hebrides Trench

The New Hebrides Trench to the south east of Solomon Islands has travel times of less than two hours. Figure A3-4 shows the 8.5 Mw, 8.0 Mw and 7.5 Mw model scenarios for the New Hebrides Trench.

Figure A3-4: New Hebrides Trench a critical source from the southeast with limited warning time (ABoM 2007).

[SOPAC Miscellaneous Report 654 – Pearce] [72]

(iii) Mariana Trench

Tsunami events from the Mariana Trench to the northwest would have longer travel times (4-6 hours) to the Solomon Islands. Figure A3-5 shows the 9 Mw and 8.5 Mw model scenarios.

Figure A3-5: Mariana Trench a critical source from the northwest with approximately four hours lead time (ABoM 2007).

[SOPAC Miscellaneous Report 654 – Pearce]