Analytical inversion for Thomsen's gamma parameter in weakly anisotropic layered media

Michael A. Slawinski, Raphaël A. Slawinski and R. James Brown

An analytic scheme for traveltime inversion in horizontally layered media exhibiting transverse isotropy with a vertical symmetry axis (TIV) is presented. It pertains to SH waves, i.e., characterized by a single Thomsen parameter, g, or to other waves exhibiting approximately elliptical velocity dependence. The proposed method incorporates ray bending at interfaces.

The suggested approach is particularly suitable for vertical seismic profiling as best providing required information. The input information consists of traveltime for obliquely travelling downgoing waves which can be measured by an offset survey, vertical wave speed from the zero-offset survey, and layer thicknesses directly from the wellbore.

Correct results necessitate high accuracy of all input parameters. The proposed inversion method is particularly sensitive to errors in measured traveltime.

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