An important step in the simultaneous interpretation or inversion of multicomponent data sets is to quantitatively estimate the ratio of P-wave velocity to S-wave velocity (VP/VS). In this endeavor, I have developed correlation techniques to determine long-wavelength components of VP/VS that can lead to more accurate measurements of rock properties and processing parameters.
P-wave reflections are correlated with converted P- to S-wave reflections (or S-wave reflections) from the same location to determine which events are related to the same subsurface impedance contrasts. Shear waves are transformed (compressed) to P-wave time via average VP/VS conjugate operators before correlation. Aided by conventional P-wave velocity information and petrophysical relationships, this technique provides optimal VP/VS estimates in a similar manner that semblance analyses provide stacking velocities. These estimates can be used to transform the entire S-wave trace to P-wave time for short-wavelength amplitude inversion. Also, a target-oriented correlation analysis quantitatively determines interval VP/VS at a specific horizon or group of horizons.
Data from vertical seismic profile (VSP) stacked traces are used to evaluate these techniques. Long-wavelength average and interval VP/VS estimates obtained from the correlation analyses agree closely with VP/VS results determined from VSP direct-arrival traveltimes.