神戸市東灘区における地震動のアレイ観測に基づく地盤震動特性

概要

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A temporary earthquake array observation was done in Higashinada of Kobe city, which is one of heavily damaged areas in the 1995 Hyogo-ken nanbu earthquake. Using records of aftershocks, we discussed site effects and propagation of seismic waves in sedimentary layers. First, we compared the ratio of the maximum amplitudes of the records to that at the reference rock site. It was found that the ratio of the maximum horizontal velocity becomes larger in the heavily damage zone than those out of the area. The basement depth is estimated from travel time difference between initial S-and SP-waves. This agrees well with results of seismic surveys. However, we found that the spectral ratios at sites in the Rokko Island are larger than those at the other sites at periods of 2 to 4 sec. This suggests the amplification of seismic waves in deep sedimentary layers. Polarization and semblance analysis of the long-period motion indicate that they are Love waves propagating from the north to the south. A multiple filtering analysis for the long-period motion clearly shows dispersive features of the Love waves.
1998-05-30