Reflection Traveltime Inversions in VTI Media

Anisotropy parameters in a VTI medium can be obtained by normal-moveout velocity analysis performed on short-spread or longspread reflection-seismic data, in combination with check-shot or well-log data. Analysis of three traveltime approximations to the actual reflection traveltime shows that each traveltime approximation has its own requirements for spread length and subsurface anisotropic parameters. When e −δ = 0 (elliptical anisotropy), all three approximations are the same as the actual reflection traveltime. When 2 . 0 − δ e , the hyperbolic and modified three-term Taylorseries approximate traveltimes largely deviate from the actual reflection traveltime. The results of the three reflection traveltime inversions by semblance scan demonstrate that the estimated anisotropy parameters are always less than but close to the actual anisotropic parameters, and that the hyperbolic traveltime and modified three-term Taylor-series inversion are not suitable for 2 . 0 > − δ e