Seismic velocity estimation and time to depth conversion of time-migrated images

We address the problem of time to depth conversion of time migrated seismic images and show that the Dix velocities estimated from time migration velocities are the true seismic velocities divided by the geometrical spreading of image rays. We pose an inverse problem: to find seismic velocities from Dix velocities and suggest two algorithms for solving this problem. One algorithm is based on the ray tracing approach, and the second is based on the level set approach. We test these algorithms on synthetic data examples and apply them to a real data example from the North Sea. We demonstrate that it is important to take into account the fact that, in laterally heterogeneous media, the Dix velocities are not equal to the seismic velocities and that the difference between the two can be significant.