f Inversion of VSP field data for anisotropy with singularities

Inversion of the parameters characterizing shear-wave splitting, provide a way of obtaining a good starting model for full-wave modelling, improving the convergence to a final waveform match. This is necessary as the shear-waves behave in a highly non-linear fashion with respect to anisotropy. To arrive at such a model for the subsurface. a two stage process is involved. Firstly, estimates for the parameters which specify the morphology of the split shear-waves are obtained, and secondly, these values are interpreted in terms a range of physically plausible anisotropic models. The estimation stage in this work is still in its infancy, however MacBeth (1990) demonstrated that it is possible using current rudimentary algorithms, to achieve a well resolved inversion result using the polarization of the leading split shear-waves, provided VSP data for several azimuths of direction are recorded. The subject of this present work is to show that these results may be used to facilitate the final fit using full-wave modelling.