2023 Volume 60 Issue 2 Pages 62-71
For a large number of earthquakes observed by KiK-net (strong earthquake observation network) in mountainous areas, etc., the surface-to-subsurface ratios of Fourier spectra of acceleration amplitudes for seismic waves were obtained, and the average of the ratios for each frequency was used as the average spectral ratio (ASR). The average value of ASR for the period 0.1 to 0.5 seconds is used as the average spectral ratio intensity (ASRI), which is an index of the seismic amplification effect at the observation point. A clear negative correlation was observed between ASRI and average S-wave velocity to a depth of 30m (AVS30). On the other hand, a weak positive correlation was found between ASRI and the curvature of the topographic index. In some cases, the influence of topography on the seismic amplification was suggested. However, there was a group of mountain slopes whose ASR did not differ significantly from that of non-mountain slopes, suggesting that mountain slopes have limited seismic amplification.
