JULY 2009, NO. 11

Contents: Earthquake Occurrences in the Northern Part of 2008-2009 • Earthquake Occurrences in the Northern Part of Indonesia 2008-2009 General Introduction Until very recently earthquakes occurrences have been reported mainly from the Sumatra Fore Arc Region, and from Sumbawa (the Lesser Sunda Islands Region, NTB and NTT). Then “the Dragon” seems to move North eastward to , at the Birds head of Papua, and in Talaud Island, Northern Minahasa Published by (See Fig. 1). PT. Asuransi MAIPARK Indonesia Eventhough not much has been Board of Advisors reported, Minahasa the Eastern tip of Frans Y. Sahusilawane ’s North Arm has been Bisma Subrata regarded as a very seismic country. But large destructive earthquakes were rare. Board of Editors On the other hand the Northern part of Mudaham T. Zen Papua has been frequented by rather Andriansyah larger earthquakes in the past. This no Fiza Wira Atmaja surprise, the large Sorong Fault skirted Ruben Damanik along the North coast of Papua and M. Haikal Sedayo continues on to the West, close to Heddy Agus Pritasa Sulawesi’s Northeast Arm. Bintoro Wisnu Jyesta Amaranggana Waspada in its earlier edition, Waspada Address No. 7, March 2008 made a comparison MARKETING DEPARTMENT in earthquake occurrences between East PT. Asuransi MAIPARK Indonesia and West Indonesia. Fig. 1. A Schematic Map showing the geographi c Setiabudi Atrium Building, Fl. 4, location of the Gorontalo Earthquake (1) , Jl. HR. Rasuna Said Kav. 62, The Gorontalo EQ. the Manokuari Earthquake (2) , and the Talaud (3) A moderate-to large earthquake of Jakarta 12920 Earthquake (Not to Scale) magnitude 7.3 to the Richter scale Tel.: (021) 521 0803 struck the center part of Sulawesi’s North Arm (Fig. 2, 3a-c, 4) on November 17, 2008. Its Fax : (021) 521 0738 epicenter lies on the north coast and its focal depth was reported at 30 km. In fact this E-mail: [email protected] earthquake is situated at the edge of the Sulawesi Sea. Nonetheless this earthquake is Website: www.maipark.com known as the Gorontalo earthquake since this city suffered the heaviest economic loss. The exact location is reported to be: 122.1 0 East and 1.29 0 North (Table 1 and 2). The quake caused excessive destruction. Refer to BNPB’s report, 1,418 houses suffered heavy damage

and 892 houses suffered minor damage. BNPB also reported 4 people perished in this disaster.

Table 1. Gorontalo Earthquake Source Parameter Magnitude 7.3 Richter Scale Location 122.1 ° East 1.29 ° North Focal Depth 30 km

Table 2. Losses Dwelling Houses Economic Losses 2,310 units IDR: 418.6 billion

Fig. 3b. Magnitude distribution for earthquake occurrences in the Western part of Indonesia for the period of 1964-2008.

Fig. 2. A tectonic map of the Eastern part Indonesia taken from Hamilton’s map (1989) with the Neogene Suture Region (top center).

Fig. 3 c. Magnitude distribution f or earthquake occurrences in the Eastern part of Indonesia for the period of 1964- 2008.

The Manokwari Earthquake The Manokwari earthquake occurred on Sunday, January 4, 2009, exactly at 04:43:54 AM, and its location is 132.783 0E, and 0.51 0 S. Its focal depth is reported at 35 km, and its magnitude is 7.6 on the Richter scale (Fig. 5).

2,146 houses were heavily damaged and 4,084 suffered intermediate and minor damage due to Manokwari quake. Even though the destruction was quite large, death toll reported was “only” four persons. Fig. 3a Earthquake distribution in Indonesia 1964 to 2008

Eventhough the magnitude is given up as 7.3 on the Richter scale, this earthquake has been classified as a very powerful one. Its focal depth is 35 km, but major ground shaking at the surface has been recorded and mentioned by the USGS (January 4, 2009) and by some eye witnesses.

Fig. 4. Earthquake occurrences in the Suture Zone in Indonesia (see Fig.2) with fault plane solutions.

Further to large destruction of houses in rural area, this earthquake also damaged number of multi-storey buildings in urban area which mainly occupied as office building and hotel.

Fig. 5 . Location of the Manokwari Earthquake

Table 3. Manokwari EQ Source Parameters Fig. 5a. A residential building (top) and a three-storey Magnitude 7.6 on the Richter scale building (below) which are damaged by Manokwari quake. Location 0.510 °S and 132.783 °E Focal Depth 35 km Epicentral Region Near the North coast of The Talaud Earthquake Papua Indonesia (Fig. 5) On February 11, 2009 at 17:34:50 UTC a strong Time of Origin 14:15:56 or 10:15:56 PM earthquake hit Talaud Islands (North Minahasa), Its geographic location: 3.902˚N, and 126.400˚E. Its focal Table 4. Exposure and Estimated Economic Losses depth was reported to be 20 km. Seismologist recorded Its Manokwari (exp.) IDR 0.9 Trill. magnitude of 7.2 on the Richter scale. Refer to BNPB (value of buildings) report 645 houses suffered heavy damage and 775 houses Kabupaten Sorong (exp.) IDR 3.6 Trill. suffered intermediate and light damage. Number of public (value of buildings) facilities including schools and hospitals were also Kabupaten Bintuni (exp.) IDR 0.3 Trill. reported suffered damages. (value of buildings) A month later, on Monday, March 16, 2009 at 14:15:56 Total Estimated Economic IDR 312,9 Billion UTC or 10:15:56 PM local time, an earthquake with a Loss magnitude of 6.3 on the Richter scale occurred in a very close location with the February earthquake. The geographic location was recorded at 3.82˚N, and Table 7. Vulnerability 126.500˚E with focal depth of 35 km. The epicentral Inventory at Talaud Islands IDR 4.7 Trill. region was Talaud Islands (North Minahasa) (Fig. 6). Inventory at Sangihe Islands IDR 3.7 Trill This epicenter is located at 2.460 km from Jakarta, 1.335 km from Manila, and 315 km from (capital city Some Remarks on the Suture Zone of North Sulawesi Province) (See Table 6 and 7). One of the most interesting features of the tectonics of Northeast Indonesia is the Neogene Suture Zone between the volcanic arc of Halmahera and the volcanic arc of Minahasa-Sangihe with a double subduction; one dipping Eastward beneath Halmahera to a depth of about 250 km, and the other one dipping Westward beneath the Minahasa-Sangihe arc to a depth of about 650 km (Hamilton, 1989). The active volcanoes of both arcs lie about 100 km above the tops of the respective seismic zones (see Fig. 7) Further up North, and slightly to the East stretches the Philippine Trench which continues on to the North, and slightly West of the Minahasa Arc and trending North-Northwest; there lies the Cotabato Trench.

This complicated double subduction feature produces an earthquake distribution pattern depicted in Fig. 7. Fig. 6a. Location of the Talaud Island earthquake on Underneath Halmahera there is already the zone of the February 11, 2009 Sorong Fault (Fig. 7). It is no wonder that this region is tectonically very active. Fortunately the exposures on both sides of the Suture Zone are relatively not as high as in many places in the Western Part of Indonesia such as the Sumatra Fore Arc Region. An East-West and a NW- SE Profile across the Suture Zone is provided by Cardwell et al 2001 (Fig. 8, 9). It is therefore imperative that a close watch should be held on this part of the world.

Fig. 6b. Location of the Talaud Island earthquake on March 16, 2009

Table 6a. Talaud EQ February 11, 2009 Source Parameters Magnitude 7.2 on the Richter scale Location 3.902 °N, 126.400 °E Focal Depth 20 km Origin Time and Date 17:34:50 UTC; Wednesday, February 11, 2009

Table 6b. Talaud EQ March 16, 2009 Source Parameters Magnitude 6.3 on the Richter scale Location 3.82 °N, 126.500 °E Focal Depth 35 km Fig. 7. Tectonics of the Eastern Part of Indonesia Origin Time and Date 14:15:56 UTC; Monday, (taken from Hamilton’s map, 1989) March 16, 2009

Fig. 9 (left) .

(a) Block diagram illustrating the geometry of the Molucca Plate being subducted in the Molucca Sea region South of Mindanao. Latitude and longitudinal are given for reference and the effect of the earth’s sphercity is included. The configuration of the plate is given by a grid of two intersecting sets of curves. One set of curve lies in the horizontal plate at 50 km depth intervals. The other set of curves is oriented down the dip of the plate and is approximately orthogonal to the first set.

Fig. 9 (b) Cross section showing the inferred geometry of the plates in the Northern Molucca sea at about 5 0N. The seas are shown in section E, F, and G: (1) thrusting of Celebes basin beneath the Sangihe Ridge at the Cotabato Trench, (2)

down-dip compression within the Molucca Plte at Fig. 8. Major tectonic feature in the Philippine and great depths, (3) down-dip compression within the Northeast Indonesia Island, modified from Hamilton Molucca Plate at intermediate depths, (4)

(1979) underthrusting of the Philippine Basin beneath the

Talaud Ridge at the Philippine Trench.

Fig. 9 (c) Cross section showing the inferred geometry of the plates in the Southern Molucca sea across the Halmahera and Sangihe island arc. (Cardwell et all, 2001).

What Underwriters Ought to Know For the time being the exposures are still very low for the Eastern Part of Indonesia. But the situation will not remain the same during the coming two decades. The pace of development will pick up albeit not yet the same like in the Western Part, but things are changing.

Look at Fig. 10. This map shows the location of gold and copper locations. Oil and gas found at the neck of the Birds’ head (Bintuni Bay) are very promising. Besides, the potential for fisheries, mariculture and fresh water aqua culture, timber and other potential for marine industry is enormous. The insurance industry should not be a late comer.

Fig. 10. Location on the gold and copper deposits and major prospect in Indonesia. Deposits are those that are either past producers or for which reserve/resource estimates are available.

References 1. Cardwell, R. K, B. L. Isack, D. E. Karig, The spatial distribution of earthquakes, focal mechanism solutions and subducted lithosphere in the Philippines and North eastern Indonesian Islands , special edition of geofisika, Indon. Aes. Of Geophysicist, Bandung, 2001. 2. Carlile, J. C. and AHG Mitchel. Magmatic arcs and associated gold and copper mineralization in Indonesia , Journal Geochemical Exploration, Elsevier, Vol. 50-NoS. 1-3, 1994. 3. Hamilton, W., Convergent plate tectonics viewed from the Indonesian Region , Geol. Indonesia, v. 12, no. 1, Jakarta, 1989.

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