f Interpreting non-orthogonal split shear waves in multicomponent VSPs

Many techniques for processing shear-wave splitting in VSP data assume orthogonality of the split shear-waves, and are consequently restricted to zero or near-offset VSPs and symmetry planes (Wintersteen and Meadows 1991; Zeng and MacBeth 1993; among others). Here, we derive equations for multicomponent seismic data (two or three sources recorded by 3C receivers) for non-orthogonal split shear-waves. The equations can be solved by the linear-transform technique (LTT) of Li and Crampin (1993) to determine the shear-wave polarizations in both zero- and offset VSPs . This method is particularly useful where orthogonal techniques often fail when deviation from orthogonality exceeds 5°, or the incidence angle exceeds 1.5°.