Broadband seismic wave radiation process of the 2000 Western Tottori, Japan, earthquake revealed from wavelet domain inversion

Abstract

We develop a new inversion method to obtain the low- and high-frequency wave radiation processes whose border is 1 Hz. In this method, we adopt a consecutive approach to evaluate the fitness between the observed and synthetic strong motions and to synthesize the waveforms. A new feature of our inversion is an evaluation of the fitness of broadband strong motions, including the high-frequency range, using the wavelet coefficient of velocity waveforms based on the frequency-dependent characteristics of seismic waves. Another new feature is the introduction into the source inversion of a hybrid Green's function, which is constructed from theoretical and empirical Green's functions for the low- and high-frequency ranges, respectively. In order to reach the global minimum by nonlinear inversion, we introduce a multiscale approach for the low-frequency inversion. After a synthetic test, the inversion method was applied to the 2000 western Tottori earthquake for three frequency bands. The low-frequency inversion (0.0625-1 Hz) reveals that the asperity extends from the southeast of the hypocenter to the shallow part of the fault above the hypocenter. The waves of 1-2 Hz are radiated most intensely from the rupture starting area of the southeast asperity. On the other hand, the higher-frequency waves of 2-4 Hz are radiated most strongly from the edge of the southeast asperity. The inversion result suggests a possibility that broadband strong motions are generated from the asperities, and the high-frequency wave radiations are particularly related to the initiation and termination of the asperity rupture. Copyright 2009 by the American Geophysical Union.