IMPROVEMENT OF THE SHAPE FUNCTION IN THE STOCHASTIC SIMULATION METHOD AND REPRODUCTION OF HIGH-FREQUENCY MOTION RECORDINGS OF THE KOBE EARTHQUAKE

摘要

The stochastic method is widely used to simulate high-frequency motions. However, it has a crucial defect that simulated high-frequency motions are underestimated in amplitude and duration except for near-fault zones.This is primarily caused by neglecting the contributions from multiply reflected and transmitted waves and scattered waves. We remove this defect from the method in a simple practical way. We firstly introduce an epicentral-distance dependent shaping window which is inferred from borehole data provided by KiK-net (Abbreviation of Kiban Kyoushin network). We secondly introduce the radiation coefficients transiting from theoretical to isotropic values along with propagation. The validity of this improved stochastic method is demonstrated by reproducing three-component acceleration time histories of the 1995 Hyogo-ken Nanbu earthquake (Kobe) in amplitude, duration, and spectra at all the sites in the Osaka basin.