A global optimization method incorporating a ray-tracing scheme is use
d to invert observations of shear-wave splitting from two near-offset
VSPs recorded at the Conoco Borehole Test Facility, Kay County, Oklaho
ma. Inversion results suggest that the seismic anisotropy is due to a
non-vertical fracture system. This interpretation is constrained by th
e VSP acquisition geometry for which two sources are employed along ne
ar diametrically opposite azimuths about the well heads. A correlation
is noted between the time-delay variations between the fast and slow
split shear waves and the sandstone formations.