Summary Wc present an alternative approach for ray based migration velocity analysis Instead ot using Kirchoff migration and offset domain Common Reflection Point (CRP) gathers we use wave equation ray parameter CRH gathers. By performing tomography in vertical travel-time (lau) space, we avoid estimating mapping velocity, instead concentrating on focusing velocity. By introducing anisotropic preconditioning oriented along bedding planes, we quickly guide the inversion Inwards a geologically reasonable model. We illustrate the benefits of our tomography method by comparing it to more traditional methods on a synthetic anticline model.

Abstract In areas of complex geology, prestack depth migration is often necessary if we are to produce an accurate image of lhe subsurface. Preslack depth migration requires an accurate interval velocity model. With few exceptions, the subsurface velocities are not known beforehand and should be estimated. When the velocity structure is complex, with significant lateral variations, reflect ion-tomography methods are often an effective tool for improving the velocity estimate. Unfortunately, reflection tomography often converges slowly, to a model that is geologically unreasonable,or it does not converge at all. The large null spate of reflection-tomography problems often forces us to add a sparse parameterization of the model and/or regularization criteria to the estimation. Standard tomography schemes tend to create isotropic features in velocity models that are inconsistent with geologv. These isotropic features result, in large part, from using symmetric regularization operators or from choosing a poor model parameterization. II we replace the symmetric operators with nonstalionary operators that tend to spread information along structural dips, the tomography will produce velocity models that are geologically more reasonable. In addition, by forming the operators in helical ID space and performing polynomial division, we apply the inverse of these space-varying anisotropic operators. The inverse operators can be used as a preconditioner to a standard tomography problem, thereby significantly improving the speed of convergence compared with the typical regularized inversion problem. Results front 2D synthetic and 2D held data are shown, in each case, the velocity obtained improves the focusing of the migrated image.