HR: 0800h
AN: U11B-0840    [Abstracts]
TI: Rupture Propagation of the 2004 Sumatra Earthquake Observed by the Dense Japanese Tiltmeter Array
AU: * Watada, S
EM: watada@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 1-1-1 Yayoi Bukyo-ku, Tokyo, 113-0032 Japan
AU: Kunugi, T
EM: kunugi@bosai.go.jp
AF: National Institute for Disaster Prevention, 3-1 Tennodai Tsukuba, Tsukuba, 305-0006
AB: From short-period and broadband P waveform array analysis, high sampling GPS analyses, and oceanic hydro acoustic array analyses, the 2004 Sumatra earthquake ruptured the source region of 1200km long from south to northward for about 8 minutes. The earthquake source rupture velocities agreed to about 2-3 km/sec but the estimated seismic energy, moment release, and displacement distributions vary among researches. The long-duration source rupture hinder the separation isolated P waves from the surface reflected PP waves theoretically arriving two minutes after P waves. Regional seismic array analysis (Kruger nad Ohrnberg 2005) separates P waveforms from other phases based on the difference of incident angles into the seismic array. HiNet (Japanese high sensitivity seismograph network) also collocates the 20Hz sampling 27bit tiltmeters. These tiltmeters act as a broadband seismic array with more than 600 stations. Tiltmeter records are converted into velocity. The dominant period of S waveforms is about 30-50 sec and the array analysis of broadband S waveform indicates three stages of rupture propagation. The first S wavepacket continues about 150 sec, the third wavepacket arriving about 400 sec after the first has the largest amplitude. Array analysis of P waveform also indicates that the largest amplitude wavepacket exists corresponding the third arrival of S wavepacket.. Incident angles and azimuth of these wavepackets show that the first wavepacket corresponding to the source rupture from Sumatra to Nicoba island, the third corresponding to the rupture near Andaman island. The second wavepacket is not clear. The difference seismic energy release between S waveforms and P waveforms may hint the change of source mechanism in the rupture propagation.
DE: 4564 Tsunamis and storm surges
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
SC: Union [U]
MN: Fall Meeting 2005