HR: 16:45h
AN: S12G-04    [PDF]
TI: Green's Functions, Source Signatures and the Normalization of Teleseismic Wavefields
AU: * Bostock, M G
EM: bostock@geop.ubc.ca
AF: Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AB: We examine the canonical source/Green's function separation problem within the context of teleseismic body wave propagation and scattering from receiver-side lithospheric/upper-mantle structure. Our principal objective is the recovery of the intramodal {\it P}-impulse response for use in multi-parameter wavefield inversions. The time-normalized transfer operator that describes the response of a 1-D stratified, elastic half-space to a plane wave incident from below, can be factored into pure transmission and free-surface reverberation parts. Assuming pre-critical interactions, the intramodal entries of the reverberation operator are always minimum phase. The intramodal entries of the transmission operator are not generally minimum phase, but they will be for {\it P}-waves in weak to moderate contrast stratification; a characteristic that, we argue, persists for the class of laterally heterogeneous media representing real Earth environments. Transformation to minimum phase thus provides a means of normalizing the source within teleseismic {\it P}-seismograms and serves to emphasize weaker secondary arrivals. The shaping filter derived from this transformation can, moreover, be applied to additional non-minimum-phase wave components to effect a similar source normalization. Minimum-phase normalization facilitates the implementation of simultaneous, source-receiver, multi-channel deconvolution within the log-spectral domain through the provision of statistical constraint equations, and facilitation of phase unwrapping. Examples using both synthetic data and seismograms from the Canadian National Seismograph Network demonstrate the recovery of accurate and reproducible estimates of the intramodal {\it P}-impulse response.
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting