HR: 16:00h
AN: S12G-01    [PDF]
TI: Hybrid Synthesis of Wave Envelopes in Random Media
AU: * Sato, H
EM: sato@zisin.geophys.tohoku.ac.jp
AF: Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Fehler, M
EM: fehler@lanl.gov
AF: LANL, Los Alamos, Los Alamos, 87545 United States
AU: Saito, T
EM: saito@zisin.geophys.tohoku.ac.jp
AF: Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AB: High-frequency seismograms of local earthquakes are mostly composed of incoherent waves that are scattered by distributed heterogeneities in the lithosphere. Although their phase variations are complex, their wave-envelopes are systematic, frequency dependent, and vary regionally. The time width of a wavelet is broadened with increasing travel distance due mostly to diffraction caused by long wavelength spectra of random velocity inhomogeneity. Coda waves are excited due mostly to large angle scattering by the short wavelength spectra. Stochastic approaches are superior to deterministic wave-theoretical approaches for modeling wave envelopes in random media. The Markov approximation for the parabolic wave equation is appropriate for the synthesis of wave envelopes around the direct arrival, and the radiative transfer theory is appropriate for modeling coda envelopes. For the synthesis of whole envelopes from the onset to coda, we propose to use the envelope derived from the Markov approximation as a propagator in the conventional radiative transfer integral equation. The effective isotropic scattering coefficient is given by the momentum-transfer scattering-coefficient, which is mostly controlled by the short wavelength spectra of random media. The envelopes resulting from the proposed hybrid method agree well with ensemble-average envelopes calculated by averaging envelopes from individual finite difference simulations of the wave equation for a suite of 2-D random media having rich short wavelength spectra.
DE: 4275 Remote sensing and electromagnetic processes (0689)
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting