STUDY OF SITE EFFECTS IN KOBE AREA USING MICROTREMORS

In this study, an attempt was made to examine the effect of site condi tions on damage distribution in the Kobe City area, after the Hyogo-ke n Nanbu earthquake of Jan. 17, 1995, using measured microtremors. A pr eliminary measurement of microtremors was done between Feb. 18 and 21, 1995. Based on the findings of the preliminary measurement, a more de tailed investigation was made between March 4 and 6, 1995. In both cas es continuous-stationary measurements and mobile measurements were mad e. The measured microtremors in the Kobe area showed site-dependent va riation in time history, spectral amplitude, spectral ratio, and predo minant period. Stiff soil sites showed lower values of amplitude both in time history and spectral amplitude, while soft and deep soil forma tions showed higher values. The predominant periods also varied in rel ation to the soil formation in some of the cases. The damage distribut ion of building structures, especially that of low-rise structures inc luding wooden houses, showed good relation with the characteristics of measured microtremors.