Multi-parametric FWI using a new parameterisation for elastic VTI media

The anisotropic elastic full waveform inversion (FWI) is important because many sedimentary rocks have anisotropic properties and seismic waves are partially affected by such properties. However, the multiparametric FWI for anisotropic media has lots of difficulties due to the complexities induced by multicomponent data and multi-mode conversions of seismic waves. As a fundamental step to design an optimal anisotropic multi-parametric FWI algorithm, we propose a new parameterisation using Poisson's ratio and Thomsen parameter, ε for the elastic VTI full waveform inversion. We first analyse why the conventional parameterisation for the VTI media fails in recovering reliable subsurface parameters at the same time. The analyses are conducted by employing a new concept of basis virtual source, which can be regarded as an elemental unit to express numerical scatterings induced by a parameter perturbation. As a result, we notice that the conventional parameters have some limitations, particularly in the aspect of the spatial coverage of the gradient direction. Numerical examples for the 2D SEG/EAGE overthrust model show that the FWI using the new parameterisation for the VTI elastic media remarkably improves inversion results without additional inversion stage unlike the hierarchical inversion.