HR: 0800h
AN: S41A-0950    [Abstracts]
TI: Dynamic fault rupture constraints to high frequency radiation of crustal earthquakes: the role of rupture velocity and fmax
AU: * Pulido, N E
EM: nelson@edm.bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention (EDM-NIED), 4F Human Renovation Museum 1-5-2 Kaigan-dori, Wakihama, Chuo-ku, Kobe, Hyo 651-0073 Japan
AU: Dalguer, L A
EM: ldalguer@moho.sdsu.edu
AF: Dept. Geological Sciences, San Diego State University, San Diego, CA 92182 United States
AB: The study of high frequency (HF) radiation of large earthquakes have been traditionally investigated by using kinematic models of the source. Some of these studies locate the HF radiation near boundaries of large slip regions (Zeng et. al. 1993, Kakehi et. al. 1996, 1997; Nakahara 1999, 2002), while others locate the HF radiation overlapping regions of large slip (Hartzell et. al 1996). However, a major limitation of all these studies is the over-simplification of the physical parameters involved in the rupture process such as the assumption of a nearly constant rupture velocity across the fault plane. Simple dynamic crack models have theoretically demonstrated that local variations of the rupture velocity play a very important role in the radiation of high frequency from the source (Madariaga 1977, 1983). In the present study we investigate the high frequency radiation of the 2000 Tottori earthquake (Japan) in two steps: First we investigate the complexity in the fault rupture by performing a spontaneous rupture dynamic model of the Tottori earthquake in the low frequency range (.1 to 1Hz). The fault friction law parameters and stress drop of the dynamic model are constrained from results of a kinematic model of source. On the other hand the rupture velocity is allowed to vary spontaneously. In the second step we calculate the high frequencies from a semi-stochastic approach that considers the radiation from a heterogenous finite fault and a frequency-dependent subfault-site specific radiation pattern model (Pulido et. al. 2004). The forward calculation of the high-frequency ground motion (1 to 20Hz) at the target observation sites is constrained by the subfault rupture times from the above dynamic model. In order to optimise the agreement to observed high frequency ground motion we use a Genetic Algorithm approach to invert for the stress drop distribution, fmax, and the high frequency decay for frequencies above fmax, by comparing the observed and simulated RMS acceleration envelopes, as well as the acceleration Fourier spectra of the waveforms. In order to effectively constraint the HF inversion, we first investigated Q and the site effects at all the KiK-Net borehole stations, by applying a spectral inversion technique (Moya et. al 2003) to 55 aftershocks of the Tottori earthquake. Preliminary results show that the high frequency radiation from the source is determined by a complex relationship between the rupture velocity, stress drop and fmax. The results are very sensitive to the dynamic model obtained. Further investigations should address the non-uniqueness of a dynamic rupture model.
DE: 7223 Seismic hazard assessment and prediction
DE: 7260 Theory and modeling
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting