Seismic waves in a stratified half space -- II. Theoretical seismograms

Abstract

For a buried source in a stratified elastic half space, the surface displacements are calculated by numerical integration of the Fourier—Bessel transform of the response. In the transform space this response is conveniently represented in terms of the reflection and transmission properties of the half space. For a layered medium this procedure avoids all problems associated with growing exponential terms in the evanescent regime. A slightly attenuative medium is assumed, so that the surface wave poles are shifted off the real slowness axis and thus a contour of integration along this axis may be employed. A general point source is represented by an arbitrary moment tensor. The procedure is illustrated by calculations of three component seismograms including all P, SV and SH contributions for body and surface waves at moderate ranges. For local earthquakes we illustrate the striking effect of focal depth and also show the effect of sedimentary cover on strong ground motion.