The Analysis of the Influence of Vs/Vp on the Elastic Impedance Inversion

Elastic impedance (EI) inversion as a popular pre-stack seismic inversion method has been studied in the past years. However, the robustness of estimating elastic parameters of P-wave velocity, S-wave velocity, and density in conventional EI inversion is still controversial, especially the accuracy of the S-wave velocity. In this paper, we show that the obvious inversion error of the Vs is associated with the accuracy of the ratio of VS to VP (VS/VP) when the three parameters are inverted. The deviation of the VS/VP in the linearized Zoeppritz equation provided by Aki and Richards results in the mismatch between the forward and backward modeling. A new kind of inversion formula containing VS/VP as the inversion parameter is proposed, by which VS can be estimated in terms of the new inverted parameter. Due to the nonlinear relationship between the new inverted term and the VS, the Newton downhill method is used to solve the nonlinear problem. The synthetic data inversion examples demonstrate the performance of the new formula.