抄録
Long-period microtremors were observed at 63 ooints in Kobe urban area after the 1995 Hyogo-ken Nanbu Earthquake. The purpose of the observation was to clarify the depth distribution of the base rock under the area. Using the observed records, horizontal-to-vertical soectral ratios were evaluated from cross-spectra of horizontal and vertical components and power spectra of vertical components. 0n the other hand, horizontal-to-vertical spectral ratios for the fundamental mode of Rayleigh wave were calculated from subsurface structure models with a different depth of the base rock. Comparing the two groups of spectral ratios, it was inferred that the base rock depth increases very sharply to about 1km on the south of the Rokko Mts. but the inclination becomes very gentle under Kobe urban area.
