HR: 17:45h
AN: S34B-08 INVITED     [Abstracts]
TI: Cross-Correlations Within an Elastic Wavefield in 2D and 3D
AU: * Sanchez-Sesma, F J
EM: sesma@servidor.unam.mx
AF: Instituto de Ingenieria, UNAM, Cd. Universitaria, Circuito Escolar s/n, Mexico, DF 04510 Mexico
AB: Multiple scattering and conversions of P and S waves in heterogeneous media result in equipartition of elastic waves which means that, in the phase space the available elastic energy is distributed equally among all the possible modes, with equal amounts in average. In such diffusive regimes the P to S energy ratio equilibrates in a universal way independent of the particular details of the scattering. We study the canonical problem of an isotropic distribution of plane waves in an homogeneous elastic medium. We show that the Fourier transform of azimuthal average of the cross-correlation between the motions at two points is proportional to the imaginary part of the exact Green tensor between these points, provided the energy ratio E_S/E_p is the one predicted by equipartition in two- and three-dimensions, respectively. These results clearly show that equipartition is a necessary condition to retrieve the exact Green function from correlations of the elastic field. However, even if there is not an equipartitioned regime and correlations do not allow to retrieve precisely the exact Green function, they may provide valuable results of physical significance by reconstructing specific arrivals. We present some numerical examples illustrating the partial recovering of Green functions. We also discuss the implications of these results for the retrieval of the surface wave terms of Green function in layered medium.
DE: 7203 Body waves
DE: 7260 Theory
DE: 7270 Tomography (6982, 8180)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: Fall Meeting 2005