P and S Wave Velocity Model Retrieved by Multi Modal Surface Wave Analysis

Near surface velocity models are needed for static corrections applied to seismic reflection data. Surface wave present in seismic records can be analysed to retrieve near surface models. In particular, the inversion of the dispersion curve related to the fundamental mode of Rayleigh wave propagation is widely used to infer S-wave velocity model but is poorly sensitive to P-wave velocity. The sensitivity to P-wave velocity can be improved including in the inversion higher modes and P-guided waves. An algorithm based on a misfit function related to the Haskell-Thomson determinant is used to handle higher modes and P-guided waves in both a Monte Carlo and a least squares inversion. A preliminary inversion is run, assuming an a priori value of the Poisson ratio, to retrieve a consistent S-wave initial model and then the inversion is run again with the P-wave velocity as a further unknown. The results of both 1D Monte Carlo inversion and pseudo-2D laterally constrained inversion confirm that this approach is a very promising tool for retrieving P and S-wave near surface models.