PS-wave Attenuation and Resolution Related to Vp/Vs Estimates

The ratio of compressional-wave (P-wave) to shear-wave (S-wave) velocity (VP/VS or γ) is an important quantity for converted P- to S-wave (PS-wave) applications. However, this process can be hampered by wavelet distortion such as attenuation and transformation from one domain to another. In this study I assess errors in VP/VS due to wavelet distortion when S-wave attenuation (1/QS) affects the bandwidth of PS-wave resolution. Error estimates are computed for thin-bed interference where the P-wave upper and lower reflections are at Rayleigh tuning. VP/VS errors are caused by subtle thin-bed phase distortions when PS-wavelets are either above or below Rayleigh tuning. Thus, when the apparent resolution of PS-waves is better than P-waves, estimated γi will be lower than the true value, and when the apparent resolution of PS-waves is poorer than P-wave, estimated γi will be higher. A field data example over the Marcellus in Pennsylvania, USA, is examined and indicates that the PS-wave has similar resolution as the P-wave (VP/VS is similar to sonic data), where VP/VS errors are small in the Marcellus shale. However, errors in shallower intervals suggest that the PS-wave has better resolution than the P-wave.