Accession Number : ADA187663

Title :   A Spectral Method for Computing Complete Synthetic Seismograms.

Descriptive Note : Final rept. 25 Oct 84-31 Dec 86,

Corporate Author : COLORADO UNIV AT BOULDER

Personal Author(s) : Harvey, Danny J

PDF Url : ADA187663

Report Date : Mar 1987

Pagination or Media Count : 36

Abstract : Much attention has been paid to the problem of the efficient computation of complete solution synthetic seismograms for flat, plane layered, laterally homogeneous elastic media and for high frequency bandwidths in the field of solid-earth geophysics. The only available methods for computing complete synthetic seismograms are computationally expensive and often suffer from numerical instabilities which limit their ranges of applicability. This report presents a new method based on a spectral representation of the solution of the elastic wave equation. Reformulating eigenvalue and eigenfunction computations avoids the numerical instabilities. A mode searching algorithm is developed which makes it possible to find large numbers of Rayleigh and Love dispersion curves efficiently and reliably. The locked mode approximation allows nearly complete synthetic seismograms to be computed using only the discrete part of the spectrum and using only normal modes with real eigen wave numbers. This is achieved by adding a high velocity cap layer to the bottom of the elastic model and by using phase velocity filtering to attenuate the spurious scattering caused by the cap layer. Comparisons of the results of the locked mode approximation with exact results obtained from other synthesis methods are presented and the limitations of the method are demonstrated and discussed. Examples of synthetic seismograms using the locked mode approximation are given along with a comparison of observed and synthetic seismograms.

Descriptors :   *SEISMOGRAPHS, *SEISMOLOGY, *COMPUTER APPLICATIONS, ALGORITHMS, BANDWIDTH, COMPUTATIONS, EFFICIENCY, EIGENVALUES, EIGENVECTORS, ELASTIC PROPERTIES, ELASTIC WAVES, HIGH FREQUENCY, HOMOGENEITY, PHASE, SCATTERING, SEARCHING, SEISMIC DATA, SOLUTIONS(GENERAL), SPURIOUS EFFECTS, VELOCITY, WAVE EQUATIONS, THESES, MATHEMATICAL MODELS

Subject Categories : Seismology
      Computer Programming and Software

Distribution Statement : APPROVED FOR PUBLIC RELEASE