Pure-mode SS-wave Reflections from P-wave Sources in Azimuthally Anisotropic Media

Early theoretical and field studies showed that P-wave sources generate a substantial amount of shear-wave energy for pure-mode (SS-wave) exploration seismology. SV-waves are created in isotropic or VTI (vertical transversely isotropic) media by either buried explosives or surface vibrator and weight drop sources. These methods have not been embraced by our industry; however, benefits could include shallow S-wave velocity model building to help PS-wave processing (CMP processing is easier), and S-wave surface-consistent residual statics. The purpose of this study is to re-examine the feasibility of recovering SS-waves generated by P-wave sources in azimuthally anisotropic media. We analyze 3D synthetic seismograms for VTI and HTI (horizontal transversely isotropic) media to demonstrate the analysis and retrieval of SS-waves. Using conventional PS-wave azimuth processing and analysis techniques, it is possible to recover both the fast and slow SV1- and SV2-waves related to vertically fractured media. Although fast and slow SH1- and SH2-waves are not excited by conventional P-wave sources in the anisotropy symmetry planes, these waves can also be recovered from paraxial azimuths up to 45 degrees. A field 3D-3C dataset over the Marcellus shale is an ideal test case due to the presence of SS-waves and S-wave splitting.