A New Parameterization for 2-D Elastic VTI Media

To improve inversion results for 2-D elastic VTI media, we introduce a new parameterization. The new parameterization introduces the Lamé constants and two new anisotropy-related parameters instead of the elastic constants (C11, C13, C33 and C44). As the Lamé constants in the new parameterization are involved with the same derivatives as in the isotropic elastic wave equations, we can use the merits of the isotropic elastic full waveform inversion (FWI). In contrast, because the new parameters are involved with the same derivatives as C11 and C13 in the conventional VTI parameterization, the new parameters retain the characteristics of C11 and C13. However, because C11 and C13 are extracted by the combination of the Lamé constants and the new anisotropy-related parameters, C11 and C13 can also be improved by the Lamé constants. These are supported by the scattering patterns of partial derivative wavefields and gradient directions for a simple two-layered model. Synthetic examples for the VTI overthrust model show that the new parameterization provides improved inversion results without additional inversion stages compared to those obtained by the conventional VTI parameterization and the hierarchical inversion strategy.