oa Density Estimation in Elastic Full Waveform Tomography

Seismic Full-Waveform Tomography (FWT) method has been used to estimate velocity structure in the subsurface using acoustic wave equation. In elastic FWT, density is usually estimated using an empirical formula or is fixed to a constant value. Almost all elastic FWT studies have ignored the influence of density that could be an important parameter. The objective of this study is to investigate the difficulty of estimating density structure and propose a new approach. In this study, we perform series of numerical simulations in order to investigate the important factor in the inversion of density structure. Our results show that it is difficult to estimate an accurate density model in the density sorely inversion because the density structure is less effective to the waveform, and the density parameter is more strongly related to the Vp parameter than Vs. We propose s new strategy based on the separations of P-wave and S-wave, and of two inversion stages: the first stage to invert Vp and density structures simultaneously, and the second one to invert Vp, Vs and density together. We conclude that this strategy indicates effective way to estimate an accurate density structure.