ESTIMATION OF HIGH-FREQUENCY WAVE RADIATION AREAS ON THE FAULT PLANE OF THE 1995 HYOGO-KEN NANBU EARTHQUAKE BY THE ENVELOPE INVERSION OF ACCELERATION SEISMOGRAMS

We estimated the high-frequency wave radiation process on the fault pl ane of the 1995 Hyogo-ken Nanbu earthquake (M-JMA = 7.2), which was a strike slip event along active inland faults, by the envelope inversio n of strong-motion acceleration seismograms. The horizontal extent of the region that radiated high-frequency (2-10 Hz) waves is about 45 km . which matches the source region estimated from the inversion of stro ng-motion displacement waveforms. High-frequency waves were mainly rad iated at the periphery of this source region, while a clear gap of rad iation was seen in the center. Along the Nojima fault, both high- and low-frequency wave radiation were large. This is explained by the fact that the rupture broke the ground surface here. High-frequency waves were also radiated at the step-over of faults between Awaji Island and the Kobe area. The step-over is interpreted to have behaved as a geom etrical barrier and generated high-frequency waves when ruptured. The radiation of high-frequency waves in the northeastern part from the hy pocenter to Kobe was small in the large moment release areas estimated From the displacement waveform inversion, and large at their peripher ies. This suggests these high-frequency waves were slopping phases fro m the subevents corresponding to the large moment release areas. The e xtent of the source region of high-frequency waves roughly matches tha t of the heavily damaged areas. We inferred that the strong high-frequ ency waves that came directly from the source was one of the causes of the heavy damage to low-rise structures.