Depth migration versus time migration: Comparison of methods and practical considerations in algorithm selection

Abstract

Two quite different time sections are encountered in exploration seismology: one is the zero-offset time section, defined physically, and another is the migrated time section, which is just a mathematical transformation of the depth section. The translation formula used in practice is complicated in mathematics and is different from the simple formula in the literature. Usually time migration works in the time domain and outputs a time section and depth migration works in the depth domain and outputs a depth section. The most important difference between the depth and time migrations, however, is how the lateral velocity changes are handled. The depth migration is more accurate, but more expensive. The choice of depth migration or time migration is dependent on the lateral velocity changes in comparison with the accuracy of the velocity model. The advantage of an accurate depth migration would disappear when the error in velocity model is larger than the lateral velocity changes. However, if cost is not a concern, an accurate depth migration is always recommended. An anisotropic velocity model should be considered only when the anisotropic influence is significant and a reasonably accurate anisotropic velocity model can be found.