Seismologic and Geodetric Investigation of the M=8.2 Irian Jaya, Indonesia Earthquake of February 17, 1996

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9706120 McCaffrey This research is to study the February 17, 1996, M=8.2 earthquake along the northwestern coast of Irian Jaya. It is among the largest in recent times and occurred in a region considered to be relatively inactive, based on past seismicity, seismic reflection profiles in the new Guinea trench, and recent geodetic measurements. The earthquake produced wide-spread destruction of coastal communities resulting largely from a tsunami and lesser effects from strong shaking. The focal mechanism suggests that the earthquake was either caused by southward thrusting of the Pacific plate beneath the island of New Guinea or by steep rupture of the oceanic lithosphere beneath the New Guinea trench. With supplemental funding from NSF to support field work, in March of 1996 the investigators operated a portable seismic network for 3 weeks, reoccupied a GPS network, and made field estimates of coseismic subsidence from changes in high tide marks. Islands around Biak are well distributed above the quake, providing a rare opportunity to study details of a great earthquake. The first-order goal is to determine which plane ruptured during the main shock. The tectonic setting provides also an opportunity to study the dynamic interaction of parallel thrust and strike-slip faults that display slip partitioning during the earthquake sequence. This grant funds the analysis of the data collected, analysis of the main shock and larger aftershocks, and an additional occupation of the GPS network to help separate coseismic slip from the rapid interseismic slip and to compare slip late in one quake cycle to that early in the next, and to interpret the significance of this great earthquake and its aftershocks. ***