Paper Summary
3-D prestack depth migration is the most time consuming part in velocity model building. To minimize the required iteration of depth migration, we first perform a demigration to the pick residual moveout (RMO) to get unmigrated time gathers, then zero-offset migration and two point ray tracing is performed iteratively to obtain the new traveltime through the updated velocity model at each iteration. There is no need for prestack depth migration at each iteration. The new approach is more rigorous than other conventional tomography approaches.
