HR: 1340h
AN: S33A-1080    [Abstracts]
TI: Spectral Reconstruction of Teleseismic Green's Functions and Source Signatures
AU: * Baig, A M
EM: abaig@eos.ubc.ca
AF: University of British Columbia Department of Earth and Ocean Sciences, 6339 Stores Road, Vancouver, BC V6T 1X4 Canada
AU: Bostock, M G
EM: bostock@eos.ubc.ca
AF: University of British Columbia Department of Earth and Ocean Sciences, 6339 Stores Road, Vancouver, BC V6T 1X4 Canada
AB: In both exploration seismic and global teleseismic studies, the signature of the source excitation must be removed from seismograms to interpret the scattered wavefield. Earthquake sources are frequently characterized by unknown and protracted rupture histories which hamper recovery of the teleseismic Green's functions in global seismology. The {\it S}-wave components of the teleseismic {\it P} Green's functions may be approximated by the so-called receiver function, the deconvolution of the {\it P} component of a given seismogram from the corresponding {\it SV} and {\it SH} components. While the receiver function approach has been very successful in constraining the {\it S}-wave velocity structure beneath stations, this technique effectively assumes that there are no discontinuities in the corresponding {\it P}-wave velocity profile. By casting the multichannel convolution problem in terms of logarithms of power spectra, the convolution of several sources on several impulse responses can be represented by a linear system that is sub-rank by one equation. In previous work, we have attempted to resolve this under-determinedness though a statistical constraint that the source signatures are independent as a final equation. However, the practical limitations in the number events we can record over a temporary array deployment mean that this constraint may not be adequately satisfied. In the present work, we demonstrate that an individual source signature can be constrained by considering cross-spectra of two seismogram components recording this event: using the phase of this cross-spectrum, the cross-spectrum of the two Green's functions can be estimated, and the power spectrum of the source signature to be estimated. These additional constraints on source signatures eliminate the necessity of appealing to the statistical independence of sources, and render the system massively over-determined. Using the well-founded assumption that the {\it P}-wave Green's function is minimum-phase, not only can we reconstruct the {\it P}-wave components of the impulse response, but highly accurate {\it SV}- and {\it SH}-wave impulse responses are also retrieved. We will present examples on real and synthetic data demonstrating the efficacy of this reconstruction technique.
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting