AMPLIFICATION OF ELASTIC-WAVES BY A 3-DIMENSIONAL VALLEY .1. STEADY-STATE RESPONSE

Steady state scattering of incident P, SV, SH and Rayleigh waves by general non‐axisymmetric three dimensional dipping layers is investigated by using an indirect boundary integral equation method. Material of the half‐space and the layer is assumed to be linear, weakly anelastic, homogeneous and isotropic. Systematic comparisons between three dimensional and two dimensional models demonstrate that the validity of a two dimensional approximation for a given basin shape may be affected strongly by changes in azimuthal angle of incidence, type of incident wave and frequency. The discrepancies of two dimensional modelling appear to be much more pronounced for the case of an incident SH wave. Another important feature of the results is the existence of strong coupling between P/SV and SH modes, which has no correspondence in two dimensional models. Such off‐azimuthal mode conversions are particularly strong for an incident SH wave. Copyright © 1990 John Wiley & Sons, Ltd