HR: 14:00h
AN: U43A-03 INVITED     [Abstracts]
TI: slip distribution and rupture history of the 2004 Sumatra-Andaman islands earthquake
AU: * Ji, C
EM: jichen@gps.caltech.edu
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Hjorleifsdottir, V
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Song, A T
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Ni, S
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Tromp, J
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Kanamori, H
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AU: Helmberger, D
AF: California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125 United States
AB: We model the slip-distribution and rupture history of the 2004 Sumatra-Andaman islands earthquake using broadband waveforms downloaded from the IRIS DMC. Three independent studies which cover a frequency band from 0.2 mHz to 5 Hz, have been preformed to understand this complex rupture process. In the first study, a preliminary model was obtained from teleseismic P and SH waves bandpassed from 2 to 200 sec. This model indicates that most of seismic energy within this frequency band was radiated from a 450 km long segment of the southern end of the aftershock zone. We verified this model by matching the static displacement at the nearby GPS site SAMP (Sampali, Medan, Sumatra, 260 km east of the hypocenter). We have also forward-computed long period (80 to 1000 sec) SEM (Spectral Element Method) waveforms at all GSN stations. The synthetics fit the observations remarkably well at period of 200 to 500 sec, but display some discrepancy at very long period (500 to 1000 sec). This preliminary result is limited because the seismic records used for inversion are not long enough to contain the energy coming from the northern segment. Our forward modeling of broadband waveforms at nearby station PALK (distance =15 deg.) as well as the discrepancies at very long periods (500 to 1000 s) suggests that some slip occurred as late as 600 sec after the origin time. This result is consistent with the second study which investigates the envelope function of high frequency (2 to 4 Hz) P waves. The azimuthal variation of the duration of envelope functions suggests a total rupture length of about 1200 km and rupture duration of 500 sec or longer. The third study investigates the normal modes spectra. The result also suggests significant slip over the northern segment of the fault. To better constrain the slip history of such a long duration earthquake, we are developing finite fault inverse procedures utilizing the longer seismic waveforms and normal-mode spectra. The inverted result will be verified using the 3D SEM simulations.
DE: 7200 SEISMOLOGY
SC: Union [U]
MN: 2005 Joint Assembly