Investigation of Eurasian Seismic Sources and Upper Mantle Structure

摘要

Complex P-SV wavegroups are sucessfully fit on vertical component seismograms for paths crossing northern Eurasia with a model having a 39-km crust and no asthenospheric low-velocity zone. Between the Moho and the 400-km discontinuity, the shear velocities found from the P-SV waveform analysis are consistently lower than those inferred from the SH waveform modeling of Grand and Helmberger. We suggest that this discrepancy is diagnostic of a polarization anisotropy associated with the olivine rich mineralogy of the thick, basalt depleted chemical boundary layer that characterizes the upper mantle beneath stable continents. The vertical resolving power of source and receiver array are investigated in determining Eurasian crustal and upper mantle structure using waveform inversion technique of Lerner-Lam and Jordan (1983). The results show that good resolution of upper mantle structure can be obtained with this method from sparse arrays of sources and/or receivers. Source arrays are particularly effective in enhancing resolution, provided that the source depths are well distributed and the source centroids and moment tensors are well determined, while receiver arrays contribute to the reduction of the variance of the model estimates. Keywords: Eurasian structure; Waveform inversion; Higher mode dispersion, Resolving power.