We study the relationship between the elastic FWI density gradient and the inverse scattering imaging condition. Due to the chain rule an elastic density gradient in different parameterization arrives at different forms. We show that in Vp-Vs-density parameterization the density gradient reduces to the inverse scattering imaging condition under the acoustic reduction. In a general elastic FWI scenario, under the same parameterization, the density gradient is typically free of long-wavelength backscattering artifacts. This gradient property suggests that the density, instead of being treated as an inversion artifact collector, can be utilized to construct meaningful and interpretable geological-geophysical objects. We argue that such a construction is closely linked to the least-squares reverse time migration (LSRTM). The difference, however, is that the FWI produces Heaviside-type step functions in the final result, whereas through pseudo-Born approximation, the result of LSRTM remains as the angle dependent band-limited Dirac delta function. We demonstrate the density inversion in elastic FWI using field data where the step functions are constructed. The field data we use has been preprocessed for imaging; despite this, however, we achieve a good match between synthetic data and observed data, including the AVO character.
Presentation Date: Wednesday, October 14, 2020
Session Start Time: 8:30 AM
Presentation Time: 8:30 AM
Presentation Type: Oral