Estimation of near surface shear wave velocity using CMP cross-correlation of surface waves (CCSW)

Roohollah Askari and Robert J. Ferguson and Kristof DeMeersman

ABSTRACT

One of the challenges of converted wave processing is to estimate a good near surface shear wave velocity model for static corrections. To this end, we have enlarged upon the idea of CMP Cross-Correlation of Surface Waves to increase lateral resolution. Our approach is fast and we believe it is more robust in the presence of variable source wavelet and noise. We cross-correlate each trace of a shot record is with a reference trace that is selected from within the shot gather based on high signal to noise ration. This step removes source effect, and converts traces to zero-phase. New midpoints that relate to the correlated traces are then calculated. We calculate the phase velocity for each CMP gather, and finally, we convert the resulting dispersion curve to a vertical shear wave velocity by an inverse procedure. Putting together all the vertical shear wave velocity profiles of all the CMP gathers, 2D images of shear wave velocity are obtained for the data set. In this study, we invert for 2D shear wave profiles for two receiver lines with different geophone spacing. We have used the models to compute converted wave receiver statics, and our results illustrate the potential use of this method for computing converted wave receiver static corrections.

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