Recovery of elastic parameters for a multi-layered transversely isotropic medium

Abstract

A method for recovery of elastic anisotropic parameters of a multi-layered medium from three-component walkaway VSP data is presented. By analysing the multi-component signals recorded by any receiver in a walkaway VSP survey, the apparent transmission velocity field for the layered media above this receiver depth is inverted to yield the effective combined elastic constants of those layers. The interval elastic parameters and the velocity fields for the interval layer of interest between two receiver depths are also efficiently determined from these. The inversion technique adopted the Levenberg–Marquardt method to recover the elastic parameters from the qP-, qSV- and SH-wave transmission travel time data. For the layered media above a given receiver, the P- and S-wave velocities (α0, β0) along the symmetry axis, and the full set of Thomsen's anisotropic parameters are recovered by our inversion approach. For the combined layer's properties, the tilt angle (ψ) of the symmetry axis from the vertical is also inverted. The inversion software was first tested on synthetic data. It was then applied to actual field data and found to give plausible results. Anisotropic parameters recovered in this way may be used to improve data processing and imaging in the presence of transverse isotropy.