Near-surface and Near-seabed S-waves from P-wave Sources

Most shear-wave (S-wave) surveys in exploration seismology are acquired with compressional-wave (P-wave) sources. These are primarily for the purpose of recording P to S converted-wave (PS-wave) reflections to image deep oil and gas targets. Essential for processing, is to have a good model of Swave properties in the overburden and near surface. These properties include not only velocities and statics, but also the presence of S-wave birefringence (splitting) in azimuthally anisotropic media. In addition to PS-waves, pure mode shear-waves (SS-waves) are excited by P-wave sources due to the elastic nature of the near surface and these can aid in velocity model building. The purpose of this presentation is to examine several applications of SS-waves and PS-waves to characterize S-wave properties of the overburden using SS-wave modes from land and marine surveys. Synthetic seismic data from an HTI medium is used to demonstrate that fast and slow SS-waves can be recovered. Also in the marine environment, S-wave resolution is typically very high near the seabed, and can provide accurate S-wave statics and velocities for prestack depth migration (PSDM). An interferometry example shows that SS-waves can be retrieved from OBC data, and a PSDM example illustrates the high resolution that can be achieved with PS-wave data.