CWP-804 Elastic full-waveform inversion of transmission data in 2D VTI media

Full-waveform inversion (FWI) has proved effective in significantly improving the spatial resolution of seismic velocity models. However, it is implemented mostly for isotropic media and the applications to anisotropic models are typically limited to acoustic approximations. Here, we develop a foundation for elastic FWI in laterally heterogeneous VTI (transversely isotropic with a vertical symmetry axis) media. The model is parameterized in terms of the P- and S-wave vertical velocities and the P-wave normal-moveout and horizontal velocities. To derive the gradients of the objective function with respect to the VTI parameters, we employ the adjoint-state method. The iterative inversion is performed in the time domain using the steepest-descent method and a finite-difference modeling code. To test the algorithm, we introduce Gaussian anomalies in the Thomsen parameters of a homogeneous VTI medium and perform FWI of transmission data for different configurations of the source and receiver arrays. The inversion results strongly depend on the acquisition geometry and the aperture because of the parameter trade-offs. In contrast to acoustic FWI, the elastic inversion helps constrain the S-wave vertical velocity, which for our model is decoupled from the other parameters.