Accession Number : ADA310774

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

Descriptive Note : Interim rept. 25 Apr-24 Oct 95,

Corporate Author : PHILLIPS LAB HANSCOM AFB MA

Personal Author(s) : Jih, Rong-Song

PDF Url : ADA310774

Report Date : 21 DEC 1995

Pagination or Media Count : 117

Abstract : Lg is often the most prominent phase on regional seismograms and hence it has been extensively used in various seismic operations: (a) detection and location, (b) source size (earthquake magnitude and explosive yield) estimation, and (c) source type identification (that is, discrimination). However, there have also been many outstanding fundamental questions regarding the excitation and propagation of the Lg phase. This report documents a comprehensive modeling study aimed at quantification of the 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 (that is, operational) application to routine processing of seismic records and it could improve the performance of seismic discriminants based on P/Lg ratios.

Descriptors :   *SEISMIC WAVES, *SEISMIC DISCRIMINATION, MATHEMATICAL MODELS, ALGORITHMS, COMPUTERIZED SIMULATION, NUCLEAR EXPLOSIONS, SPATIAL DISTRIBUTION, STRUCTURAL ANALYSIS, ELASTIC PROPERTIES, UNDERGROUND EXPLOSIONS, WAVEGUIDES, SEISMIC DETECTION, FINITE DIFFERENCE THEORY, SEISMIC DATA, WAVE PROPAGATION, EARTH CRUST, ATTENUATION, HETEROGENEITY, CALIBRATION, EARTHQUAKES, REVERBERATION, SEDIMENTS, PLANE WAVES, SEISMIC SIGNATURES, PRIMARY WAVES(SEISMIC WAVES), WAVE PACKETS, SEISMOGRAPHS.

Subject Categories : Seismology

Distribution Statement : APPROVED FOR PUBLIC RELEASE