Improving converted-wave (P-S) moveout estimation

Robin Tage Slotboom, David W. S. Eaton, Donald C. Lawton

The moveout characteristic of converted-wave (P-S or S-P) seismic data differs subtly, yet significantly, from the moveout characteristic of unimodal (P-P or S-S) seismic data. Converted-wave velocity analyses and moveout corrections that the use the standard hyperbolic approximation can be problematic, primarily when data with offset-to-depth ratios are of 1:1.5 or more are used. Improved traveltime estimation can be achieved by adding another degree of freedom into the analysis, for example by using higher-ordered traveltime equations. However, in doing so, simplicity in the analysis is lost, and more effort is required for accurate seismic data processing.

In this paper we present a new formula that combines the compactness of the standard equation (currently the industry workhorse) with the accuracy of higher-ordered equations. It is derived both empirically and analytically and is shown to be in the form of a time-shifted hyperbola---a curve which others already have shown better fits the travetime curve of unimodal data. The performance of the new equation is illustrated with a number of practical examples.