KIRCHHOFF MIGRATION AND VELOCITY ANALYSIS FOR CONVERTED AND NONCONVERTED WAVES IN ANISOTROPIC MEDIA

We develop asymptotic expressions and outline a procedure to perform Kirchhoff migration in anisotropic media. This technique is based on a new Green's tensor representation for azimuthally isotropic media obtained by using analytical forms for the ray amplitudes and traveltimes. Since in real applications the usage of general anisotropy in a migration scheme will be limited by the availability and reliability of the velocity model considered, we also develop a new anisotropic velocity analysis scheme to generate realistic anisotropic models for migration in azimuthally isotropic media for nonconverted and converted qP-qSV waves. This velocity analysis technique is based on nonhyperbolic traveltime-offset formulas explicitly given in terms of the five elastic constants of azimuthal isotropy. The imaging technique is applied to nonconverted-as well as converted-wave surface seismic data. In both cases the method provides accurate images of the subsurface. Even with a weak to moderate percentage of anisotropy, we show that an isotropic migration algorithm cannot properly image the subsurface. This paper provides new nonconventional techniques for the velocity analysis and migration in anisotropic media and shows the feasibility of exploiting converted and nonconverted waves.