Seismic response of 2-D absorbing structures by the ray method

Summary

A method of seismic response analysis of 2-D inhomogeneous structures, based on the ray method and on the application of the Debye procedure to include slight absorption, is presented. Program package RESPO, designed for such an analysis of the seismic response on the free surface of a general 2-D laterally varying, geological near-surface structure assuming P, SV or SH plane-wave incidence from below, is briefly described. The pckage is tested on the classical model of a sedimentary basin. The study diffres from previous applications of the ray method to the basin model in the following aspects. The frequency-domain approach is used. A comparison of the ray method results with the results of the discrete wavenumber method for long periods is made. More attention is paid to the analysis of the formation of the wave field. This analysis reveals two main types of wave propagation inside the basin: the dominant horizontally propagating local interference waves and less expressive vertically propagating waves in the central part of the basin. Effects of slight absorption (Futterman's causal absorption) are considered. The absorption causes a decrease in amplitudes and time delays at later times. The decrease in the amplitudes is not so expressive because of large periods and relatively short travel times of the waves investigated.

Keywords

Seismic response, ray method, frequency-domain approach, slight causal absorption, classical basin problem.

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