A new parameterisation with poissons ratio for multi-parametric FWI in isotropic elastic media

For elastic full waveform inversion, several kinds of parameterisation have been used. The resolution of inversion results is dependent on the parameterisation, because different parameterisations yield different radiation patterns of partial derivative wavefields for each parameter. Accordingly, it is important to find an optimal parameterisation for inversion. Analysing the radiation patterns of the conventional parameterisation (i.e., the velocity-density parameterisation, but similarly the impedance-density and the Lame constants-density parameterisation) for the P-wave velocity, we note that the conventional parameterisation has some limitations that the resolution of the gradient direction is poor and sensitive to the variations of Poisson' ratio. These limitations result from the absence of P-S, S-P and S-S scattered waves in partial derivative wavefields with respect to the P-wave velocity. To compensate for these limitations, we propose a new parameterisation using Poisson's ratio, which makes the virtual source for the P-wave velocity have double-coupled forces and generate P-P, P-S, S-P and S-S scattered waves. Numerical examples show that the FWI for the P-wave velocity can be enhanced using the new parameterisation.