Reverse Time Migration of Decoupled qP- and qSV-wave in TTI Media with the Optimal Quadratic Approximation
(2.Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, Shandong, China 266000)
【Abstract】In the seismic data processing, if the influence of anisotropy and the symmetry inclination of tilted transversely isotropic (TTI) media changes are ignored, the imaging position of targets will be deviated, and even the amplitude imbalance may be caused by the caustic problem. The pseudo-shear-wave interference exists in the forward modeling and reverse time migration (RTM) when using the conventional TI coupled pseudo-acoustic wave equations, and the numerical simulation is unstable when the anisotropy parameter ε < δ. We proposed a new approach to solve the problem. By referring to the experience of predecessors, we used the idea of the optimal quadratic approximation (OQA) to approximate the accurate phase velocity formula in VTI medium, and approximate phase velocity formulas of qP-wave and qSV-wave with relatively high accuracy are obtained respectively. Then, based on the approximate phase velocity formula, the decoupled qP-wave and qSV-wave equations in TTI media were derived. We used a hybrid finite-difference/pseudo-spectral method to solve the wave equations to realize efficient and stable numerical simulation. Finally, high-precision, high-efficiency, and stable TTI media forward modeling and RTM were established. Numerical simulation results show that the proposed method can achieve migration imaging in complex TTI media.
【Keywords】 reverse time migration (RTM); TTI media; pure qP-wave; pure qSV-wave; optimal quadratic approximation (OQA); hybrid finite-difference/pseudo-spectral method;
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