An optimal parameterization for full waveform inversion in anisotropic media

Full waveform inversion (FWI) in transversely isotropic media usually requires abundant a priori information, like well data and smoothness assumptions, to make the FWI converge to a plausible solution. The proper model parameterization in transversely isotropic (TI) media with a vertical symmetry axis (VTI) can alleviate some of these limitations. Considering the limitations of our field data acquisition to constrain the long wavelength vertical velocity (the depth information) in VTI media, we test a parameterization using the horizontal velocity, ζ and ϵ that is relatively immune from this specific lack of long wavelength description of the background model. We test our claim with a VTI Marmousi II data set modeled under the elastic assumption. The initial velocity is extracted from a smoothed version of the true normal moveout and horizontal velocity models to represent what we expect from the long wavelength analysis of our data (traveltimes). Having an inaccurate δ (equal to zero in this test) caused the inversion parameterized by the vertical velocity, δ, and ϵ to yield worse results than the inversion parameterized by the horizontal velocity, ζ and ϵ.