Estimation of Hierarchical Structured Strong Motion Generation Patch Causing Seismic Damage

Seismic damage is strongly influenced by the characteristics of strong motion at the natural period of about 1 second. For predicting near fault strong motion in this period range, it is important to adequately evaluate the heterogeneity of the slip distribution of the source rupture process as well as the effects of the complex subsurface geology. The characteristics of velocity pulse waves, directly leading to seismic damage, derived from forward rupture directivity effects are significantly affected by the size and the slip velocity function of the strong motion generation patches (SMGPs). So, it is necessary to evaluate these parameters accurately (Kawase et al., 2000). We developed a technique for estimating rupture process assuming a distinctive SMGP by waveform fitting considering the 3-D subsurface geology using 3-D reciprocal Green's functions and examined the validity of the technique by numerical experiment (Matsushima et al., 2001). In this study, we extended the technique to resolve multiple SMGPs and applied this technique to resolve the size and slip velocity functions of the SMGPs of actual earthquakes. We used data of the Off Miyagi, Japan, earthquake of 1978 recorded at stations of Public Works Research Institute of Japan. By using the sharp velocity pulses, with dominant period of about 1 second, in the data as target, we found that we need relatively small patches hierarchically existing inside the asperities derived from previous source inversions (e.g. Yamanaka and Kikuchi, 2003).