HR: 0800h
AN: S41A-0238    [Abstracts]
TI: Full Waveform 3D Synthetic Seismic Algorithm for 1D Layered Anelastic Models
AU: * Schwaiger, H F
EM: hfschwa@sandia.gov
AF: Sandia National Laboratories, PO Box 5800, MS 0750, Albuquerque, NM 87185-0750, United States
AU: Aldridge, D F
EM: dfaldri@sandia.gov
AF: Sandia National Laboratories, PO Box 5800, MS 0750, Albuquerque, NM 87185-0750, United States
AU: Haney, M M
EM: mhaney@usgs.gov
AF: Sandia National Laboratories, PO Box 5800, MS 0750, Albuquerque, NM 87185-0750, United States
AB: Numerical calculation of synthetic seismograms for 1D layered earth models remains a significant aspect of amplitude-offset investigations, surface wave studies, microseismic event location approaches, and reflection interpretation or inversion processes. Compared to 3D finite-difference algorithms, memory demand and execution time are greatly reduced, enabling rapid generation of seismic data within workstation or laptop computational environments. We have developed a frequency-wavenumber forward modeling algorithm adapted to realistic 1D geologic media, for the purpose of calculating seismograms accurately and efficiently. The earth model consists of N layers bounded by two halfspaces. Each layer/halfspace is a homogeneous and isotropic anelastic (attenuative and dispersive) solid, characterized by a rectangular relaxation spectrum of absorption mechanisms. Compressional and shear phase speeds and quality factors are specified at a particular reference frequency. Solution methodology involves 3D Fourier transforming the three coupled, second- order, integro-differential equations for particle displacements to the frequency-horizontal wavenumber domain. An analytic solution of the resulting ordinary differential system is obtained. Imposition of welded interface conditions (continuity of displacement and stress) at all interfaces, as well as radiation conditions in the two halfspaces, yields a system of 6(N+1) linear algebraic equations for the coefficients in the ODE solution. An optimized inverse 2D Fourier transform to the space domain gives the seismic wavefield on a horizontal plane. Finally, three-component seismograms are obtained by accumulating frequency spectra at designated receiver positions on this plane, followed by a 1D inverse FFT from angular frequency ω to time. Stress-free conditions may be applied at the top or bottom interfaces, and seismic waves are initiated by force or moment density sources. Examples reveal that including attenuation stabilizes the numerical calculations, and reduces wraparound artifacts associated with the spatially-periodic 2D Fourier transform. Sandia National Laboratories is a multiprogram science and engineering facility operated by Sandia Corporation, a Lockheed-Martin company, for the US DOE under contract DE-AC04-94AL85000.
DE: 0902 Computational methods: seismic
DE: 3285 Wave propagation (0689, 2487, 4275, 4455, 6934)
DE: 7203 Body waves
DE: 7260 Theory
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting