CRP-Scans from 3D prestack depth migration - A new tool for velocity model building

Migration velocity analysis allows the checking and improvement of the complex velocity models required for 3D pre-stack depth imaging. The new migration velocity method we propose is free from any assumptions regarding the migration velocity model. Our method is based on the classic CRP (Common Reflecting Point) gathers from common-offset migration, extended by a scan of homothetic velocity perturbations. The scan of velocity perturbations around the complex 3D velocity model is economically emulated by a scaling of the precomputed traveltimes. Optimal alignment is directly observed. If present, an alignment at depth Z and perturbation y gives directly a new depth location and a velocity perturbation. A table of siech new depth locations and velocity perturbations allows the product ion of an updated velocity model.