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

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.