Generation of Basin-Induced Surface Waves Observed in the Tokachi Basin, Hokkaido, Japan.

Abstract

Recent studies on basin-induced surface waves observed in deep earthquake seismograms at basin stations have shown that the excitation strength of the surface waves varies with earthquakes, as well as the basin shapes. We investigated the variation in basin-induced surface waves with earthquakes by a combination of observational and numerical studies, selecting the Tokachi Basin, Hokkaido, Japan, as the test site. A detailed comparison between the seismograms observed at the basin and rock sites for nearby and intermediate-depth earthquakes shows that the excitation strength of basin-induced surface waves with a predominant frequency of about 0.3 Hz strongly depends on the frequency content and incident angle of S-waves impinging on the basin. The observational results are complemented with two-dimensional modelings of SH and P-SV wavefields using the pseudospectral method, which successfully reproduce the effects of the frequency content and incident angle of incident S-waves. The simulation results also show that the basin edge slopes play an important role in the excitation of basin-induced surface waves.