HR: 1340h
AN: S53B-1267    [Abstracts]
TI: Radiative Energy Transfer of Elastic Waves in Random Media – Three-component Envelopes and Numerical Validation
AU: * Korn, M
EM: mikorn@uni-leipzig.de
AF: Institute for Geophysics and Geology, University Leipzig, Talstrasse 35, Leipzig, D-04103, Germany
AU: Przybilla, J
EM: jprzybill@web.de
AF: Institute for Geophysics and Geology, University Leipzig, Talstrasse 35, Leipzig, D-04103, Germany
AB: Short period wave propagation through the lithosphere results in complex wavetrains that are mainly composed of waves multiply scattered at small-scale heterogeneities of the Earth medium. Often it is useful to focus on bandpass-filtered envelopes of recorded seismograms instead of the full waveforms, as envelopes are stable features that allow the retrieval of statistical parameters of the lithospheric heterogeneity. Parameters like rms velocity and density fluctuation, correlation distance or scattering attenuation are informations closely related to stratigraphy, stress distribution, crack density, pore fluids etc. We present a Monte Carlo scheme for the solution of the three-dimensional radiative transfer (RT) equations for energy transport in elastic media with randomly fluctuating velocity and density. It includes mode conversions between P and S wave energy, and considers the frequency dependent directional scattering patterns following from Born approximation in continuous random media. By splitting S energy into two parts with orthogonal linear polarization we keep the polarization information of S energy without using the Stokes vector concept. The method offers a convenient way to synthesize complete three-component mean square envelopes of bandpass-filtered high-frequency wavefields in the presence of small-scale random heterogeneity starting from the first P wave onset until the late S wave coda. Validation of the method is achieved through a comparison with average mean square envelopes from full 3D wavefield simulations for the whole envelope shape and with the analytical Markov approximation for time windows around the ballistic arrival times. RT yields accurate envelope shapes even for parameter ranges where strong forward scattering occurs. Peak amplitudes, pulse broadening and coda decay at long lapse times are correctly modelled. A breakdown of RT is observed in the vicinity of a point source: waveform modeling shows that even for a pure compressional source some per cent of outward propagating shear wave energy are generated by near-source scattering that are not explained within the framewok of Born approximation.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting