Anisotropy estimate from vertical (VSV) and horizontal (VSH) components of S-wave velocity using ray-based tomography

The acquisition of S-wave seismic data, separating SH (orthogonal to the seismic line) and SV (parallel to the seismic line) wavefields on the same seismic line, is not so frequent. However, this type of acquisition allows obtaining important information on the investigated area; in particular the anisotropy of the sediments, which can be detected from the differences between the corresponding two velocity fields. In this work, we analysed the SV- and SH-wave data in order to answer two questions: how can we estimate anisotropy from the comparison of the velocities of the SV and SH wavefields? What information can be obtained about the dip and strike angles of the anisotropic layers from this analysis? For this purpose, we used the travel time tomography to obtain the two velocity fields (VSV and VSH) and to exploit the computed ray paths from which we can know the directions of each ray segment crossing the model, associated with each VS component. We, then, used them, together with the VSV /VSH values obtained from the tomography, to estimate the anisotropy and the orientation of the anisotropic layer, defined by the slope (dip) and the azimuth angle (strike). Furthermore, we tried to define a possible relationship between the VSV and VSH components with the anisotropy parameters, the direction of the rays and the geometry of the anisotropic layer.