EFFECTS OF THE IRREGULAR UNDERGROUND STRUCTURES ON SEISMIC WAVE PROPAGATION NEAR THE WESTERN EDGE OF THE NOBI PLAIN

摘要

In this paper, we discuss the propagation process of ground motions generated by two earthquakes through the analysis of seismograms recorded on rock and sediment sites. Significant later phases following the S-wave arrivals in horizontal components often appear in the ground motions recorded in the sedimentary plain. We applied 2-D finite difference method to simulate the later phases during the earthquakes observed at the sediment sites using the subsurface structures derived from the seismic and micro tremors prospecting process.The results indicate that when considering then as basin excited waves, the characteristics of the simulated waveforms, including the later phases, display good agreement with the observed seismograms. Moreover, the earthquake motion characteristic was clarified by the propagation process of seismic waves in the western part of Nobi plain. We also clarified effects of the irregular underground structure on seismic wave propagation.