Effects of Surface Geology on Seismic Motions

Analysis and Simulations of Seismic Motions in a Sedimentary Basin

Abstract

Effects of surface geology on seismic motions are investigated using observed seismograms by an array across the Kyoto basin extending from the rock outcrop near the eastern margin to the center. By a comparison with low-pass-filtered seismograms in the basin sites, the spatial wave-form variation and elongation of duration of the S-wave portion (from the onset of S-wave to a later part where amplitudes decrease to a specified low level) are found. The phase and group velocities of the wavelets in the S-wave portion suggest that these characteristics of the seismic motion in the Kyoto basin are primarily caused by the excitation of surface waves at the eastern margin of the basin.
To reproduce the recorded seismograms in the Kyoto basin, the extended Aki and Larner method is used. Though insufficient in amplitude, the simulated seismic waves exhibit the spatial wave-form variation and the elongation of duration time due to surface waves generated at the eastern margin of the basin.