A Robust Algorithm and Associated QC for Finding the Anisotropy Directions for Converted Wave Data

摘要

Shear wave splitting, also called birefringence, is the phenomenon by which an incident S wave travels at two different velocities depending on the angle between the wave polarization and the so-called natural directions of the anisotropic medium; When the polarization is parallel to the fast (or slow) direction a single arrival is observed. However, for intermediate polarization angles, two arrivals are observed with their amplitude and polarity determined by the angle of the wave's polarization with the natural directions. This well known property gives a direct observation of the fracture directions, even though wide-azimuth P-wave data can also give such an estimate through a rather sophisticated processing sequence. In this paper we propose a robust method for estimating the natural directions based on the direct least-squares fit of the observation to a 1D, HTI model of the converted waves. The result of this algorithm is illustrated using synthetic and real data.