GENERATION OF BASIN-INDUCED SURFACE-WAVES OBSERVED IN THE TOKACHI BASIN, HOKKAIDO, JAPAN

Recent studies on basin-induced surface waves observed in deep earthqu ake seismograms at basin stations have shown that the excitation stren gth 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 studi es, 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 th e excitation strength of basin-induced surface waves with a predominan t frequency of about 0.3 Hz strongly depends on the frequency content and incident angle of S-waves impinging on the basin. The observationa l results are complemented with two-dimensional modelings of SH and P- SV wavefields using the pseudospectral method, which successfully repr oduce the effects of the frequency content and incident angle of incid ent S-waves. The simulation results also show that the basin edge slop es play an important role in the excitation of basin-induced surface w aves.