TRUE-AMPLITUDE SEISMIC MIGRATION - A COMPARISON OF 3 APPROACHES

Knowledge of elastic parameter (compressional and shear velocities and density) contrasts within the earth can yield knowledge of lithology changes. Elastic parameter contrasts manifest themselves on seismic re cords as angle-dependent reflectivity. Interpretation of angle-depende nt reflectivity, or amplitude variation with offset (AVO), on unmigrat ed records is often hindered by the effects of common-depth-point smea r, incorrectly specified geometrical spreading loss, source/receiver d irectivity, as well as other factors. It is possible to correct some o f these problems by analyzing common-reflection-point gathers after pr estack migration, provided that the migration is capable of undoing al l the amplitude distortions of wave propagation between the sources an d the receivers. A migration method capable of undoing such distortion s and thus producing angle-dependent reflection coefficients at analys is points in a lossless, isotropic, elastic earth is called a ''true-a mplitude migration.'' The principles of true-amplitude migration are s imple enough to allow several methods to be considered as ''true-ampli tude.'' I consider three such migration methods in this paper: one ass ociated with Berkhout, Wapenaar, and co-workers at Delft University; o ne associated with Bleistein, Cohen, and co-workers at Colorado School of Mines and, more recently, Hubral and co-workers at Karlsruhe Unive rsity; and a third introduced by Tarantola and developed international ly by many workers. These methods differ significantly in their deriva tions, as well as their implementation and applicability. However, the y share some fundamental similarities, including some fundamental limi tations. I present and compare summaries of the three methods from a u nified perspective. The objective of this comparison is to point out t he similarities of these methods, as well as their relative strengths and weaknesses.