SITE EFFECTS IN HIROSHIMA PREFECTURE, JAPAN DURING THE 2001 GEIYO EARTHQUAKE OF MARCH 24, 2001

摘要

During the 2001 Geiyo earthquake of March 24, 2001, large shaking was observed over a wide area of Chugoku and Shikoku district, western Japan. The observed PGA during the main shock showed large differences among several sites where the focal distances were almost equal. This is considered to be due to the regional differences of site effects. In this study, first, in order to grasp site effects within Hiroshima prefecture, we estimated the predominant period of the ground in the linear condition and during the 2001 Geiyo earthquake by using various methods ever before proposed, from microtremors and seismic motion at the site of the K-NET, the KiK-net and the SIIN (Seismic Intensity Information Network) in Hiroshima prefecture. In addition, by comparing these results, we considered the nonlinearity of the soil during the main shock, and the relations between the characteristics of strong ground motion and site effects. As a result, we found that the H/V spectra were able to estimate the predominant period of the soil stably, strong nonlinear behavior of the ground that occurred at many sites during the mainshock, and a reason for the high acceleration that contains many short period waves observed at most sites during the mainshock, which is due not only to the source but also to site effects.