HR: 14:30h
AN: U43A-05    [Abstracts]
TI: Very Long Period Normal Mode Analysis on 2004 Sumatra Giant Earthquake
AU: * Song, T A
EM: alex@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Tromp, J
EM: jtromp@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Kanamori, H
EM: hiroo@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Ji, C
EM: jichen@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Hjorleifsdottir, V
EM: vala@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Ni, S
EM: stone@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Helmberger, D
EM: helm@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd, Pasadena, CA 91125 United States
AB: 2004 Sumatra giant earthquake is the largest event since 1964 Alaska earthquake and Harvard CMT gives a moment magnitude of 9.0 .Such a shallow thrust event produced huge tsunami across the Indian ocean and cause tremendous damages. However, seismic stations around globe honestly record the ground motion and provide an unprecedented dataset to retrieve details of source processes of such a giant event, while entire seismic frequency band (0.3 mHz ~ 4 Hz) can be used. Although aftershock zone extends about 1200 km north to the Andaman Island, direct mapping from the length of the aftershock zone to the rupture length is not straightforward. Teleseismic finite fault inversion (Ji et al) first gives slip distribution over a 400 km fault surface and promises a large slip about 100 km north of the CMT location. 3-D SEM synthetics based upon this finite fault model produce a very good fit to the 200-500 secs surface waves directivity (Hjorleifsdottir et al). However, high frequency P-wave envelope (Ni et al), very long period (500-1000 secs) surface waves (Hiroo et al) and the 0S2 normal mode splitting pattern suggest the rupture may actually extend further to the north and produce significant long period energies. We focus on the normal mode analysis of very long period at 0.2-3 mHz. Very long period records from GSN, Geoscope, TriNet and Berkerley netwok are collected and analyzed. Large numbers of records show clear splitting pattern of the gravest mode 0S2 and other modes due to rotation, ellipticity and 3-D heterogeneities. We compute coupled-mode synthetics to fully take into account the effect of rotation, ellipticity and 3-D Earth structure. Synthetics from a point CMT source and a finite fault model (Ji et al) are compared with the data. Preliminary result indicates long period moment (< 1 m Hz )deficit that is not explained by the 400 km finite fault model.
DE: 7200 SEISMOLOGY
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory and modeling
SC: Union [U]
MN: 2005 Joint Assembly