for Crustal Structure

Abstract We describe the use of reflected PP, SS, and converted PS/SP phases in a joint inversion to determine P- and S-wave velocity-depth functions. For an adequate determination of Poisson's ratio, the P- and S-wave velocity functions must be coupled in the inversion scheme. This coupling can be at-tained in different ways. In this article, we use the PS/SP converted phases to achieve it. In order to model gradient zones and to prevent any bias due to our choice of parameterization, our models consist of a large number of constant-velocity thin layers. The solution of the inversion problem estimates the thick-nesses of these layers. The number of unknowns (layer thicknesses) is greater than the number of data points and the one-dimensional inverse problem is an underdetermined system of equations. A weighted amped least-squares inver-sion algorithm using the (r,p) formulation is used. The input data for this inverse problem consist of intercept-time ray-parameter pairs picked from (r,p) slant-stacked wide-angle seismic reflection source gathers. When this procedure is used to invert only a single type of reflected waves, then the solution is strongly biased by the assignment of the data picks, ('c,p) pairs, to a particular layer. By using the (~',p) picks for the reflected PP, the reflected SS, and the converted PS/SP in a single joint inversion, the algorithm becomes more robust. Fur-thermore, the resolution of the P and S velocity-depth functions is greatly in-creased. The resolution kernels become sharper, decreasing the width of the main lobe by 10 to 50 % and increasing their height by 20 to 40%. This increase in resolution in the velocity-depth functions can produce a decrease of approx-imately 50 % in the error estimates of Poisson's ratio profiles