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Source: "http://www.eeri.org/Reconn/Irian/Irian_Jaya.html"


EERI SPECIAL EARTHQUAKE REPORT - MAY 1996

The February 17, 1996 Irian Jaya Earthquake and Tsunami

The information in this report was collected by an International Tsu-nami Survey Team (ITST), consist-ing of scientists and engineers from Indonesia, Japan, and the USA. The team visited the af-fected area from March 4 to 8, 1996.


Introduction

On February 17, 1996 at 05:59 GMT (14:59 local time) a major (MW = 8.2) earthquake occurred near Biak Island, Indonesia (S 0.6o, E 136.5o). It generated a deadly tsunami which reached a maximum measured height of 7.7 m. As of March 4, the official death toll from the earthquake and tsunami included 107 at Biak Island and 3 at Yapen Island. Fifty-one persons remained missing. About 100 per-sons were seriously injured, and 10,000 were made homeless. Biak and Yapen Islands are situated off the north shore of the Irian Jaya portion (western half) of the island of New Guinea.

Earthquake

Previous earthquakes in the area occurred in 1914 (7.9), 1957 (7.5) and 1979 (7.9). The duration time of rupture for the 1996 event was reported at 28 seconds. The Har-vard "quick" CMT solution sug-gests a MW = 8.2 low-angle thrust event in the New Guinea Trench, at 15 km depth, with a rupture length of 180 km and width of 50 km. However, USGS calculations indicate Mw = 7.9 and a depth of 21 km; the University of Tokyo reports Mw = 8.0 at a 33 km depth; and Caltech calculates MW = 8.1 at 33 km depth. The Biak earthquake was followed within one day by a flurry of aftershocks featuring an unusual diversity of focal mechanisms: thrust, normal, and strike-slip. The thrusting nature of the event suggests a complicated tectonic interaction for this region.

The epicenter was located in the Pacific Ocean north and east of Biak Island, a long, narrow strip of land (about 150 km by 30 km) which runs roughly east-west across the northern end of the Teluk Cenderawasih bay. Yapen Island, of similar size and orien-tation, lies about 50 km south of Biak, also in Teluk Cenderawasih.

In the village of Bosnik in eastern Biak, almost all the houses col-lapsed due to ground shaking. Many sand boils were observed by the ITST in this area of soft sand. In northern Biak 11 persons were killed, 183 houses collapsed, and 192 houses were heavily damaged by the shaking.

Tsunami

The earthquake generated a large tsunami, which struck the Irian Jaya coast with heights of about 5-7 meters. Reported tsunami heights include:

4 m at Manokwari (western New Guinea)
7 m at Sarmi (central New Guinea)
6-7 m at Korim (northern Biak)
3-5 m at Biak
7 m at Yapen Island


The tsunami caused damage as far away as Japan, where a wave height of nearly 1 m was reported and several fishing boats were washed away. A tsunami warning was issued at 17:00 local time in Japan; the first waves struck about 20 minutes later. No severe damage occurred in Japan, although this was the largest tsunami generated by a far-field earthquake to be recorded since the 1960 Chile earthquake and tsunami.

The ITST collected information on tsunami runup heights from meas-urements of clear tsunami traces and from eyewitness reports. On the northern coast of Biak, facing the tsunami source, the heights were 3-5 m, the largest measured on the island. Especially large tsunamis were observed in small bays such as Korim and Waru, suggesting concentration of tsu-nami energy or seiche action in the bays. The eastern part of Biak is surrounded by a shallow sea with many small islands. This region, close to the tsunami source, did not experience tsunamis as great as did the northern shore.

The maximum tsunami height of 7.7 m was measured at Farusi, Wardo in western Biak, which is located on the side of the island furthest from the tsunami source. A tsunami phenomenon such as a trapped wave on a coral reef may have caused this local phenomenon.

The most severe damage due to the tsunami occurred at Korim, where the height was 4-5 meters and the inundation area about 700 m long and 400 m wide. Sixty-four of the dead and 18 missing people were reported from the area in and around Korim. About 380 homes were completely destroyed by the inundation.

Remarkable sand deposition and erosion were observed along the coast at Korim. The volume of deposited sand was estimated to be about 3,000 m3. The volume of erosion estimated is less than that of deposition, suggesting that the tsunami transported the sand from the shallow sea bottom in the area around Korim.

In eastern Biak, local people report that the level of high tide is now 0.5 to 1.0 m higher than in the past, indicating the land in that area has subsided due to the earthquake.

To assist in planning the ITST survey, the tsunami simulation model TSUNAMI was used to esti-mate the probable tsunami heights along the Irian Jaya coast. Actual measurements on Biak Island compared well to the predicted values.

ITST Members

Indonesia: Mr. Subandono Dipo-saptono and Mr. Rahman Hidayat of BPPT; Dr. Nanang Tyas Puspito and Mr. Hamzah Latief of ITB; and Mr. Fusuni of BMG.

Japan: Dr. Fumihiko Imamura of Tohoku University, reader; Mr. Tomoyuki Takahashi, Mr. Ho Jun Lee, Mr. Shun-ichi Koshimura, Mr. Nobuya Horuchi, and Mr. Kazumori Kurayoshi of Tohoku University; Dr. Hideo Matsutomi of Akita University; Dr. Kouji Kofune of Port & Harbor Research Institute; Dr. Gary Watson of Kyoto University; and Dr. Yoshinobu Tsuji of the University of Tokyo.

USA: Mr. Andy Moore of the University of Washington; and Mr. Utku Kanoglu and Mr. Jose Berrero of the University of Southern California.

The reproduction and distribution of this report were funded by National Science Foundation Grant #CMS-9526408, EERI's Learning From Earthquakes Project.

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Korem Beach after earthquake -korem- North Biak, Korem Beach

Korem village in the North coast of Biak Island.


 About 50 meter from the beach.
  

Collected pictures 
from the field work in Biak, March 5 - April 5, 1996.