Earth Planets Space, Vol. 57 (No. 7), pp. 571-590, 2005
Yoshiaki Shiba1 and Kojiro Irikura2
1Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba 270-1194, Japan
2Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
(Received January 7, 2004; Revised May 17, 2005; Accepted May 18, 2005)
A source inversion method using very fast simulated annealing is proposed to estimate the earthquake rupture process, and associated radiation of broadband strong ground motions. We invert the displacement and velocity motions separately to estimate the spatio-temporal distributions of effective stress and moment. The developed method is applied to the near-source strong motions in the frequency range up to 5 Hz from the 1997 Izu-Hanto Toho-Oki earthquake (MJMA 5.9). Results of the displacement inversion indicate that for this earthquake the seismic moment is mainly released from the shallower region and the northern area from the hypocenter. Similar results are obtained from the velocity inversion, and the variation of the effective stress also exhibits a similar behavior to the moment distribution. Based on the inversion results, we propose a characterized source model that consists of the finite number of asperities and a background area with uniform effective stresses. The broadband ground motion simulation demonstrates that the characterized source model successfully reproduces the observed ground motions in spite of the simplification of actual (inverted) source process. This suggests our proposed inversion method and source characterization process are suitable for the strong-motion prediction that reflects the high-frequency radiation from an actual earthquake.
Key words: Waveform inversion, simulated annealing, empirical Green's function, effective stress, characterized source model.