Abstract

We estimate strong motion generation areas that reproduce near-source ground motions in a broadband frequency range (0.2-10 Hz) using the empirical Green's function technique. The strong motion generation areas are defined as extended areas with relatively large slip velocities within a total rupture area. Four M 6 class (the 1997 Kagoshima on March and May, 1997 Yamaguchi, and 1998 Iwate) and several moderate-size earthquakes in Japan were analyzed. We examine the relationship between the strong motion generation area and the area of asperities, which is characterized based on heterogeneous slip distributions estimated from low-frequency (<1 Hz) waveform inversions (Somerville et al., 1999). We performed waveform fitting in acceleration, velocity, and displacement, then obtained the strong motion generation area occupying about a quarter of the total rupture area. The size and position of the strong motion generation area coincide with those of characterized asperities. We find self-similar scaling of seismic moment to both the size of the strong motion generation area and the rise time for a magnitude range of analyzed earthquakes. Based on our results, we propose a characterized source model for the broadband ground-motion simulation, which consists of strong motion generation areas with large slip velocities and a background slip area with a small slip velocity. Waveform modeling of the characterized source model suggests that the strong motion generation areas play important roles in simulating broadband ground motions and have the potential to be an about 10-MPa stress-release area on the fault.

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