EXTRACTION OF P-WAVES AND S-WAVES FROM THE VERTICAL COMPONENT OF THE PARTICLE-VELOCITY AT THE SEA-FLOOR

At the boundary between two solid media in welded contact, all three c omponents of particle velocity and vertical traction are continuous th rough the boundary. Across the boundary between a fluid and a solid, h owever, only the vertical component of particle velocity is continuous while the horizontal components can be discontinuous. Furthermore, th e pressure in the fluid is the negative of the vertical component of t raction in the solid, while the horizontal components of traction vani sh at the interface. Taking advantage of this latter fact, we show tha t total P- and S-waves can be computed from the vertical component of the particle velocity recorded by single component geophones planted o n the sea floor. In the case when the sea floor is transversely isotro pic with a vertical axis of symmetry, the computation requires the fiv e independent elastic stiffness components and the density. However, w hen the sea floor material is fully isotropic, the only material param eter needed is the local shear wave velocity. The analysis of the extr action problem is done in the slowness domain. We show, however, that the S-wave section can be obtained by a filtering operation in the spa ce-frequency domain. The P-wave section is then the difference between the vertical component of the particle velocity and the S-wave compon ent. A synthetic data example demonstrates the performance of the algo rithm.