A study of the strong ground motion of the western Hidaka, Hokkaido earthquake

An attempt is made to model strong ground motion from the western Hidaka earthquake of January 23, 1981. First, the source parameters for this event are obtained from a study of teleseismic P and S waves. Parameter values are: focal depth = 110 km, fault strike = 248, dip angle = 80, rake angle = 97, source process time = 3-4 sec, and seismic moment = 2.2 x 10 to the 26th power dyne-cm. Then synthetic strong-motion seismograms are calculated for the source parameters obtained and the assumed plane-layered earth model. These seismograms are compared with the observed JMA strong-motion seismograms at seven stations in Hokkaido. The duration and amplitude behavior of observed strong-motion can be explained by the simple source and earth models, except data from Tomakomai, Urakawa and Obihiro whose observed seismograms show waves with abnormally large amplitude after the direct S wave arrival. These abnormal strong-motions may be due to propagational effects introduced by local crustal structure.