Waveguide Effects of Large-Scale Structural Variation, Anelastic Attenuation, andRandom Heterogeneity on SV Lg Propagation. A Finite-Difference Modeling Study

摘要

This report documents a comprehensive modeling study aimed at quantification ofthe individual effect of several major factors that affect Lg propagation. Two techniques are specifically designed for this project: (1) a pure Lg wave packet suitable for triggering the linear finite-difference (LFD) calculations, and (2) a simple, causal method to incorporate spatially-varying anelastic attenuation into LED simulations. A variety of mechanisms responsible for Lg blockage / weakening are carefully evaluated. These mechanisms include (a) large-scale structural variations and discontinuities, (b) an elastic attenuation, and (c) small-scale random heterogeneities. A Lg path-correction procedure is proposed to correct for these effects as well as the geometrical spreading. This procedure has an immediate, operational application to routine processing of seismic records and could improve the performance of seismic discriminants based on P/Lg ratios.