f Optimal estimation of crack strike

It has been suggested (Crampin et al. 1989) that the study of shear-wave splitting may yield valuable infonnation about the stress- and crack-geometries within reservoirs for hydrocarbon production. Shear-waves upon entering an anisotropic medium split into (usually) two components, with the faster component polarized parallel to the strike of vertical parallel cracks in the rockmass. Detennining the polarization of this leading split shear-wave for sub-vertical raypaths, will give infonnation about the strike of aligned vertical cracks, and hence the preferential directions of fluid flow within a reservoir. The time-delay between the arrival of the first and second split shear-waves gives the percentage anisotropy of the medium along the particular raypath, and from this crack density and porosity may be inferred.