Abstract:

Conventional three-term AVA inversion methods are based on the assumption that γ (the ratio of S-wave velocity to P-wave velocity) is a constant value usually considered to be 0.5, while γ is horizontally and vertically varied gradually in many cases. The estimated parameters of the inversion is bound to deviate from its true values with γ invariably being 0.5.  and the selection γ  needs to be reasonably. Based on Bayesian theory, we presents a nonlinear pre-stack seismic AVA inversion using successive iterative method, which considered the ratio’s initial background varying horizontally and vertically and being calculated by the-given initial model, and the nonlinear inversion problem was solved by successive iteration. The proposed method gived a reasonable solution for the selection of γ and solved the nonlinear problem caused by variable ratio γ . And the accuracy and stability of the three-term AVA inversion were improved.

Key words: AVA inversion, nonlinear problem, variable ratio of S-velocity to P-velocity, successive iteration, Bayesian theory