Wavelet-preserved PP- and PS-wave registration

Abstract

Calibration of PP- and PS-wave reflection events is a crucial step in multicomponent seismic data inversion and quantitative analysis. This paper presents a workflow of calibration including an optimized estimation of the P- to S-wave velocity ratio and wavelet preservation after a PS-wave trace transformation to the PP-wave two-way time. The optimized velocity ratio is obtained from the spectral analysis of correlation coefficients versus perturbations of a time-variant velocity-ratio function. This analysis may also be conducted in a target-oriented fashion which involves not only searching for the additive perturbation but also the gradient of the local velocity ratio, to overcome possible ambiguities in the correlation spectrum. However, when a PS-wave trace is transformed from the PS time to the PP time, the PS reflection wavelets along the trace are compressed. This wavelet distortion needs be removed to preserve the original PS-wave frequency content, before further inversion processing. Wavelet compression means stretching in the frequency spectrum, and such spectral stretching is time variant depending upon the local P- to S-wave velocity ratio. Thus, the restoration is implemented on the time?frequency spectrum in the Gabor transform domain. Thereafter, wavelet-preserved PS-wave reflections, presented in PP time, may be used in a PP- and PS-wave joint inversion.