Waveform Modeling of the Crust and Upper Mantle Using S, Sp, SsPmP, and Shear-Coupled PL Waves; Final rept. 1 Oct 2004-30 Sep 2007

摘要

We developed a waveform modeling code that computes synthetic seismograms with a parallelized reflectivity method and fits the observed waveforms by global optimization. Assuming a 1-D, isotropic, layered Earth, our code computes synthetic seismograms for all layers, frequencies, and ray parameters. It implements a global optimization algorithm using Very Fast Simulated Annealing that allows for broad model space search so as to rind the global minimum, and hence minimizes dependency on the starting model. Our method also computes the Posterior Probability Densities and correlation matrices to evaluate the uniqueness of the resulting models and trade-offs between individual model parameters. We applied the code to determine the crust and upper mantle structure beneath permanent broadband seismic stations in Africa, China, and Canada using large teleseismic earthquakes recorded at these stations. We modeled the S, Sp, SsPmP, and shear-coupled PB waves from these earthquakes and our P- and S-wave velocity models compare well with, and in some cases improve upon the models obtained from other existing methods. Our use of the shear-coupled PB phase wherever available improved constraints on the models of the lower crust and upper mantle.