EVALUATION OF SITE EFFECTS ON RESPONSE SPECTRA OF GROUND MOTIONS OBSERVED DURING THE 1987 CHIBA-KEN-TOHO-OKI EARTHQUAKE

Abstract

Site effects on response spectra of ground motions observed at 173 sites during the 1987 Chiba-ken-toho-oki earthquake (M = 6.7) were evaluated. The results indicate that 1) the site effects are significant on motions with periods longer than 0.2 second, 2) geomorphological land classification is more appropriate for evaluating the site effects than soil classification or surface geology, 3) the site amplifications at longer periods have stronger dependence on the average shear-wave velocity of ground, and 4) the average shear-wave velocity is a useful predictor for the site amplifications at periods of 0.7 to 1.5 seconds.