Shear waves (S-waves) radiated from explosives and vertical sources have recently been investigated for land seismic exploration to exploit conversion to compressional waves (P-waves) as primary reflections (SP-waves). It is claimed that radial-S and transverse-S modes are generated in all directions. Assuming isotropy, several case studies have processed SP-waves with intriguing but low frequency images. Most land converted P- to S-wave surveys exhibit azimuthal anisotropy that result in a low frequency response if not properly corrected. I compute S-wave radiation in orthorhombic (ORT) media by utilizing slowness vector components to demonstrate the properties of fast S- and slow S-waves. My focus is the near vertical angles, 0° to 35°, because at greater angles S-waves are typically in the P-wave evanescent range and cannot excite SP-waves. Although S- and S-waves can be confused with S- and S-waves, they have specific azimuthal amplitude properties consistent with source-generated shear stresses projected into principal symmetry planes of the earth natural coordinate system. S-waves radiate only in fast and slow vertical symmetry planes and S-waves do not exist. Furthermore, I generate seismic responses to illustrate S- and S-waves polarized parallel and perpendicular to fractures. Radiated S-waves in ORT media will result in azimuthal variations of SP-wave amplitude, phase and timing, and present additional processing and imaging challenges.
Presentation Date: Tuesday, October 16, 2018
Start Time: 8:30:00 AM
Location: 213A (Anaheim Convention Center)
Presentation Type: Oral
