HR: 16:30h
AN: S12G-03    [PDF]
TI: Estimation of two dimensional von Karman stochastic parameters from the seismic coda
AU: * Poppeliers, C
EM: poppelie@caam.rice.edu
AF: Rice Center for Computational Geophysics, 6100 Main Street Rice University Mail Slot 126 P.O. Box 1892, Houston, TX 77005 United States
AU: Levander, A
EM: alan@rice.edu
AF: Rice Department of Earth Science, 6100 Main Street Rice University Mail Slot 126 P.O. Box 1892, Houston, TX 77005 United States
AU: Symes, W W
EM: symes@caam.rice.edu
AF: Rice Department of Computational and Applied Mathematics, 6100 Main Street Rice University Mail Slot 134, Houston, TX 77005 United States
AB: Coda waves are generated from singly and multiply- scattered primary waves in the Earth. The scattered wavefield is composed of converted phases, transmissions, and reflections arising from three dimensional fluctuations in seismic velocities and density. Statistical models of the complex medium are customarily used to explain seismic scattering. Our goal is to invert the coda directly for stochastic properties of the medium through which the seismic energy travels. We characterize the medium with the von Karman autocorrelation model which can accurately model the statistical distribution of velocity/density variations of the crystalline portions of the Earth's crust. Synthetic data generated through von Karman media closely resemble real data. The von Karman autocorrelation model mimics the Earth's self affine nature and can be described in two-dimensions by three parameters; 1) the horizontal characteristic length, 2) the vertical characteristic length, and 3) the Hurst exponent, which describes the roughness of the statistical model. We present two inversion schemes to estimate von Karman parameters. In the first scheme, we show that inverting seismic array data for the lateral characteristic length is possible, but that the inversion has to be calibrated against the central frequency of the input seismic wavelet. In the second inversion scheme, we make use of the multiplicative relation between the power spectra of the observations and that of the source pulse and the stochastic medium. Thus, if we have a good estimate of the seismic pulse, we can invert directly for von Karman parameters. In the absence of complete knowledge of the pulse, we can formulate a nonlinear inversion and estimate the seismic pulse and the von Karman parameters simultaneously. The products of our inversions are cross sections of stochastic properties that can define different areas of texture and/or fabric in the Earth. We demonstrate our inversion on synthetic data as well as a seismic reflection section from the CDROM experiment in the western U.S. With two dimensional, synthetic seismic reflection data, we show that we can recover the dip-dependant lateral characteristic length. Additionally, we present results of inverting for the lateral characteristic length using the CDROM seismic reflection dataset. We claim that inverting for lateral characteristic length can be a useful tool to place bounds on the base of the crust, which is difficult to interpret deterministically in the processed seisic line. Although preliminary results of inverting for the vertical characteristic length with synthetic data are promising, we are still in the process of refining the process. Namely, we find that the primary limitation of the inversion is accurate information of the source pulse. However, with a reasonable estimate of the source pulse power spectrum non-linear inversion holds promise.
DE: 0902 Computational methods, seismic
DE: 0935 Seismic methods (3025)
DE: 7203 Body wave propagation
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2003 Fall Meeting