ACOUSTIC-ELASTIC COUPLED FULL-WAVEFORM INVERSION IN THE LAPLACE DOMAIN WITH SCALED GRADIENT FOR IMPROVED DENSITY RECOVERY

Abstract

Acoustic-clastic coupled full-waveform inversion in the Laplace domain is well suited for recovering P- and S-wave velocity (V-p and V-s, respectively), and density from marine seismic data because it can simulate waves that are generated in the fluid (sea water) and propagate into the solid (seafloor). However, density is not recovered as reliably as V-p and V-s. In this study, we show that the density recovery procedure using full-waveform inversion for acoustic-elastic coupled media can be improved by scaling the gradient for the steepest descent operation. Gradient scaling is a heuristic approach that multiplies the gradient by the square of the gradient summed in the depth direction. We found that this scaling scheme resulted in more accurate density as well as attenuated numerical artefacts. To validate the scaling scheme, we illustrate both synthetic and real data examples.