Manual seismic reflection tomography

Prestack depth migration needs a good velocity model to produce a good image; in fact, finding the velocity model is one of the goals of prestack depth migration. Migration velocity analysis uses information produced by the migration to update the current velocity model for use in the next migration iteration. Several techniques are currently used to estimate migration velocities, ranging from trial and error to automatic methods like reflection tomography. Here, we present a method that combines aspects of some of the more accurate methods into an interactive procedure for viewing the effects of residual normal moveout corrections on migrated common reflection point (CRP) gathers. The residual corrections are performed by computing traveltimes along raypaths through both the current velocity model and the velocity model plus suggested model perturbations. The differences between those sets of traveltimes are related to differences in depth, allowing the user to preview the approximate effects of a veloci...