Site amplification of ground motions during aftershocks of the 1995 Hyogo-ken Nanbu earthquake in severely damaged zone: array observation of ground motions in Higashinada ward, Kobe City, Japan

Abstract

Site amplifications during aftershocks of the 1995 Hyogo-ken Nanbu earthquake were examined in and around the disaster area of Higashinada ward. Five temporary stations together with the KOB station (CEORKA) were installed just after the main shock to arrange an array for strong ground motion observations across a severe damage band about 1.5 km wide. We estimated a thickness of about 1 km for the sedimentary basin just under soil sites using SP-converted waves recorded at all soil sites. Waveform simulations using a dislocation point source in a horizontally stratified medium were performed to explain the observed records at both the rock and soil stations. We found that large amplifications at the soil sites were generated by a thick sedimentary layer including low-velocity surface layers. The heavy damage caused by the main shock is therefore strongly connected with the sedimentary structure.