DIFFRACTION OF P, SV AND RAYLEIGH WAVES BY TOPOGRAPHIC FEATURES: A BOUNDARY INTEGRAL FORMULATION

A method is presented to compute the diffraction of P , SV , and Rayleigh waves by an irregular topographic feature in an elastic half-space. It is based on an integral representation of the diffracted elastic fields in terms of single-layer boundary sources that is derived from Somigliana's identity. Introduction of boundary conditions leads to a Fredholm integral equation of the second kind for boundary sources. A discretization scheme based on the numerical and analytical integration of exact Green's functions for displacements and tractions is employed. Calculations are performed in the frequency domain and synthetic seismograms are obtained using the fast Fourier transform. In order to give perspective on the range of effects caused by topographic anomalies, various examples that cover extreme cases are presented. It is found that topography may cause significant effects both of amplification and of deamplification at the irregular feature itself and its neighborhood, but the absolute level of amplification is generally lower than about four times the amplitude of incoming waves. Such facts must be taken into account when the spectral ratio technique is used to characterize topographical effects.