3-D seismic wavefield can only be handled with 3-D processing, and more effectively with 3-D depth migration methods, because it contains signals from all possible directions. I assume in this study that the only data that is at my disposal are the time migrated maps.
In geological areas where lateral velocity variations are present, time migrated images or maps do not represent the proper position of seismic reflections Hatton et al. (1981). Therefore, it is necessary, before applying a depth migration to the time migrated section to correct this problem. This is done using a principle of de-migration. Then depth migration is performed.
De-migration process moves time migrated sections to their original (observed) time, using the velocity model applied for time migration. In my previous work, de-migration is achieved via ray-tracing and uses GOCAD as a tool to represent the 3-D surfaces under investigation. This ray-tracing algorithm performing de-migration and depth migration has been tested on several examples and produces well positioned depth maps. In some cases, this method cannot carry out the de-migration of the initial time model. As a matter of fact, the algorithm fails when the dip of the layers is too important with respect to the velocity model used. This limitation drove us to investigate another way to perform de-migration.