HR: 1340h
AN: S13B-0204    [Abstracts]
TI: Rupture process of 2004 Sumatra mega quake by very broad band seismic analysis: Performance of real time Ocean Hemisphere Network
AU: * Ishihara, Y
EM: y-ishihara@jamstec.go.jp
AF: IFREE, JAMSTEC, Syowa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Suda, N
EM: suda@geol.sci.hiroshima-u.ac.jp
AF: Faculty of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, 739-8526 Japan
AB: Tele-seismic body wave analysis is one of most efficient method to study source rupture process for ordinary earthquake. However in case of 2004 West coast off Northern Sumatra earthquake, excited seismic wave is dominant of long period component and shows long duration P and S wave records. Therefore we can_ft extract pure direct body wave records for contamination of other seismic phases. It is difficult to analyze the overall rupture process. According to tsunami generation analysis and aftershock distribution, rupture zone is seemed that extend to northern area. The macroscopic image of earthquake is basic information and constraint for detail analysis of rupture process. 2004 Sumatra mega quake excites large amplitude earth_fs free oscillation which amplitude depends on its source size. The free oscillation is recorded by broadband global seismic network. In this study, we analyze ultra long period oscillation modes whose periods are greater than 1000 sec and evaluate macroscopic source image. OHP seismic network, operated in Western Pacific region, also records ultra long period seismograms and detects oscillation mode. We examined the quality of seismic records and excluded off-scale and/or non-linear behaving seismograms. By this screening, Inuyama(INU,Japan) and Jayapura (JAY, Papua) stations_f data have enough quality for free oscillation analysis. We used 0.1Hz sampling data and width of data window is about 1 week. We performed FFT and picked up amplitude of each mode after preprocessing and exclusion filter for earth_fs tide. We aimed at 0S0 mode firstly. The 0S0 mode is recorded same amplitude theoretically elsewhere and its amplitude depends on dip-slip amount on the fault. It is convenient to evaluate lower limit of total seismic moment. When we supposed 10 degree of fault dip angle, seismic moment is greater than twice of Harvard CMT solution. The comparison for amplitudes of ultra long period modes shows moment magnitude is 9.3 in case of fault mechanism obtained Harvard CMT. The initial phase of this mode suggests that source time is 300 to 500 sec. The discrepancy between free oscillation and body wave analysis is important information for later part of rupture process of Sumatra quake. We also performed full seismic source modeling by overall frequency band of displacement records. We aimed longer period greater than 50 sec. The full green functions are calculated by summation of normal modes. The modeling shows that source time is around 350 sec and seismic moment is comparable to one obtained longer period analysis. The moment release is one-sided in southern part of the aftershock area. On the other hand, tsunami analysis and geodetic observation suggests northern part also has fault slip. The discrepancy means that this mega shock have hybrid type, ordinal seismic source and very slow geodetic slip, sources.
DE: 7215 Earthquake source observations (1240)
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: Fall Meeting 2005