Biak Earthquake

Aftershock and GPS study of M=8.2 Biak earthquake of February 17, 1996

Rob McCaffrey, Fauzi, Masturyono, Colleen Stevens, John Nabelek, Bernd Schurr, Yehuda Bock, Cecep Subarya, Toto Puntodewo (RPI, OSU, Meteorology & Geophysics Agency, BAKOSURTANAL)

Following the M=8.2 Biak quake, we monitored aftershocks for 3 weeks using the PASSCAL RAMP seismographs, and re-occupied a GPS network. The GPS site in S Biak moved over 1 meter to the NNE while the Yapen site moved about 20 cm NNW. We also measured the subsidence of Biak Island by looking at changes in the high-tide marks. Parts of the NE side of the island subsided by 2 meters while the S and W sides dropped by less than 1 meter. The large gradients in subsidence to the south and west suggest that the S edge of the rupture zone was beneath N Biak Island. See the subsidence map and dislocation model. The horizontal and vertcal coseismic displacements can be explained by either a gently, S-dipping fault or a steep, N-dipping fault. The well-located aftershocks will tell the difference, but that work is in progress. The EDR aftershocks suggest that the S-dipping plane ruptured.

Maps

Harvard CMTs in New Guinea region(19K GIF)
GPS results 1991-1993(21K GIF)
Coseismic displacements and aftershocks (9K GIF)
Subsidence and dislocation model (12K GIF)
PASSCAL RAMP stations(7KB GIF)
EDR aftershocks(13K GIF)

Field Photos