Analytic Solution to NMO-Velocity Surface for TTI Media and Computation of Effective NMO Velocity

摘要

TI (Transversal Isotropy) media is often used in seismic exploration research at present. Reflection moveout of pure modes in anisotropic media recorded on conventional-length spreads can be still described by a normal-moveout (NMO) velocity that depends on the orientation of the common-midpoint (CMP) line. NMO velocity contains information about the parameters of anisotropic velocity field. For obtaining relationship between the measured NMO velocity and anisotropic parameters, some authors studied NMO-velocity solutions for some special TI media (Thomsen, 1986; Tsvankin, 1995, 1997; Grechka, 1998). However, all these NMO-velocity solutions were obtained on the horizontal plane, and only fit for a TI layer. If a stack of TI layers separated by plane dipping interfaces is involved, these solutions can't be directly used to compute effective NMO velocities by applying Dix-type averaging and differentiation algorithms developed by Grechka and Tsvankin (2002), and Christoffel equations of TI layers need to be solved respectively.