EVALUATION FOR LOCAL SITE EFFECT OF SEDIMENTARY BASIN TAKING INTO ACCOUNT INCIDENT WAVE FIELD

Local site effects of two alluvial sedimentary basins at Kuno in Ashigara valley and at Takeyama in Miura peninsula were evaluated under strong motion array seismographs observation. The horizontal spectral ratios of the gravelly soil's sediments at Kuno were constant in the component along the S wave's principal axis corresponded to the focal radiation pattern. On the soft clay's sediments at Takeyama, the spectral ratios to a reference point at the outcrop of bedrock were constant by considering seismic incident angle. Thus the site effects computed by two-dimensional analytical method agree with the observed spectral ratios by considering the incident wave field related to the source and path effects.