Earthquake Occurrences in the Northern Part of Indonesia

Transcription

1 JULY 2009, NO. 11 Contents: Earthquake Occurrences in the Northern Part of Indonesia Published by PT. Asuransi MAIPARK Indonesia Board of Advisors Frans Y. Sahusilawane Bisma Subrata Board of Editors Mudaham T. Zen Andriansyah Fiza Wira Atmaja Ruben Damanik M. Haikal Sedayo Heddy Agus Pritasa Bintoro Wisnu Jyesta Amaranggana Address MARKETING DEPARTMENT PT. Asuransi MAIPARK Indonesia Setiabudi Atrium Building, Fl. 4, Jl. HR. Rasuna Said Kav. 62, Jakarta Tel.: (021) Fax : (021) maipark@maipark.com Website: Earthquake Occurrences in the Northern Part of Indonesia 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 Gorontalo, Manokwari at the Birds head of Papua, and in Talaud Island, Northern Minahasa (See Fig. 1). Fig. 1. A Schematic Map showing the geographic location of the Gorontalo Earthquake (1), the Manokuari Earthquake (2), and the Talaud Earthquake (3) (Not to Scale) Eventhough not much has been reported, Minahasa the Eastern tip of Sulawesi s North Arm has been regarded as a very seismic country. But large destructive earthquakes were rare. On the other hand the Northern part of Papua has been frequented by rather larger earthquakes in the past. This no surprise, the large Sorong Fault skirted along the North coast of Papua and continues on to the West, close to Sulawesi s Northeast Arm. Waspada in its earlier edition, Waspada No. 7, March 2008 made a comparison in earthquake occurrences between East and West Indonesia. The Gorontalo EQ. A moderate-to large earthquake of magnitude 7.3 to the Richter scale struck the center part of Sulawesi s North Arm (Fig. 2, 3a-c, 4) on November 17, Its epicenter lies on the north coast and its focal depth was reported at 30 km. In fact this earthquake is situated at the edge of the Sulawesi Sea. Nonetheless this earthquake is known as the Gorontalo earthquake since this city suffered the heaviest economic loss. The exact location is reported to be: East and 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.

2 Table 1. Gorontalo Earthquake Source Parameter 7.3 Richter Scale East 1.29 North 30 km Table 2. Losses Dwelling Houses Economic Losses 2,310 units IDR: billion Fig. 3b. distribution for earthquake occurrences in the Western part of Indonesia for the period of Fig. 2. A tectonic map of the Eastern part Indonesia taken from Hamilton s map (1989) with the Neogene Suture Region (top center). Fig. 3c. distribution for earthquake occurrences in the Eastern part of Indonesia for the period of The Manokwari Earthquake The Manokwari earthquake occurred on Sunday, January 4, 2009, exactly at 04:43:54 AM, and its location is E, and S. Its focal depth is reported at 35 km, and its magnitude is 7.6 on the Richter scale (Fig. 5). Fig. 3a Earthquake distribution in Indonesia 1964 to ,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.

3 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. of the Manokwari Earthquake Table 3. Manokwari EQ Source Parameters 7.6 on the Richter scale S and E 35 km Epicentral Region Near the North coast of Papua Indonesia (Fig. 5) Time of Origin 14:15:56 or 10:15:56 PM Table 4. Exposure and Estimated Economic Losses Manokwari (exp.) IDR 0.9 Trill. (value of buildings) Kabupaten Sorong (exp.) IDR 3.6 Trill. (value of buildings) Kabupaten Bintuni (exp.) IDR 0.3 Trill. (value of buildings) Total Estimated Economic Loss IDR 312,9 Billion Fig. 5a. A residential building (top) and a three-storey building (below) which are damaged by Manokwari quake. The Talaud Earthquake On February 11, 2009 at 17:34:50 UTC a strong earthquake hit Talaud Islands (North Minahasa), Its geographic location: N, and E. Its focal depth was reported to be 20 km. Seismologist recorded Its magnitude of 7.2 on the Richter scale. Refer to BNPB report 645 houses suffered heavy damage and 775 houses suffered intermediate and light damage. Number of public facilities including schools and hospitals were also reported suffered damages. A month later, on Monday, March 16, 2009 at 14:15:56 UTC or 10:15:56 PM local time, an earthquake with a magnitude of 6.3 on the Richter scale occurred in a very

4 close location with the February earthquake. The geographic location was recorded at 3.82 N, and E with focal depth of 35 km. The epicentral region was Talaud Islands (North Minahasa) (Fig. 6). This epicenter is located at km from Jakarta, km from Manila, and 315 km from Manado (capital city of North Sulawesi Province) (See Table 6 and 7). Fig. 6a. of the Talaud Island earthquake on February 11, 2009 Table 7. Vulnerability Inventory at Talaud Islands Inventory at Sangihe Islands IDR 4.7 Trill. IDR 3.7 Trill Some Remarks on the Suture Zone 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. Underneath Halmahera there is already the zone of the 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. of the Talaud Island earthquake on March 16, 2009 Table 6a. Talaud EQ February 11, 2009 Source Parameters 7.2 on the Richter scale N, E 20 km Origin Time and Date 17:34:50 UTC; Wednesday, February 11, 2009 Table 6b. Talaud EQ March 16, 2009 Source Parameters 6.3 on the Richter scale 3.82 N, E 35 km Origin Time and Date 14:15:56 UTC; Monday, March 16, 2009 Fig. 7. Tectonics of the Eastern Part of Indonesia (taken from Hamilton s map, 1989)

5 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. 8. Major tectonic feature in the Philippine and Northeast Indonesia Island, modified from Hamilton (1979) Fig. 9 (b) Cross section showing the inferred geometry of the plates in the Northern Molucca sea at about 5 0 N. 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 great depths, (3) down-dip compression within the Molucca Plate at intermediate depths, (4) 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. 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.

6 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, 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, Hamilton, W., Convergent plate tectonics viewed from the Indonesian Region, Geol. Indonesia, v. 12, no. 1, Jakarta, Your Reliable Partner in Catastrophe Risk Transfer