Zero-Offset Migration

The main problem with the complex Fourier migration algorithm described above is that it is computationally expensive. However, by looking at the zero-offset section in Figure 5, we see that simple poststack migration will not be satisfactory. Since the salt body is present, a depth migration will help to restore the salt to its correct thickness. Also, with a more complex velocity function, there is a better chance of stacking out a majority of the multiple energy, which is very dominant in the CMP stack. In poststack migration, the object is to collapse diffractions, steepen dips, and uncross bow ties.

Using a poststack phase-shift operator, we can put the dips of the synclinal structure into the correct position, and the bow ties can be uncrossed. However, that is only a very small part of the image. Moreover, the times of those events are unlikely to be correct, especially under the salt. After migration it is still impossible to see under the salt, where the fault blocks are. Therefore, a complex prestack algorithm, though computationally expensive, becomes necessary in this type of complex geologic setting.