Nowadays, a standard industrial seismic processing almost always involves the constant-velocity dip moveout correction. Two main features make the process attractive. First, the computational cost is low compared to prestack migration in both two-dimensional and three-dimensional processings. Secondly, because constant-velocity dip moveout is ``independent of velocity'', it may come before velocity analysis, removing the effects of dip Forel and Gardner (1988).

However, the hypothesis of constant velocity is somewhat inconsistent with the concept of velocity analysis which results in the construction of a depth-variable velocity model. Recently, several methods for depth-variable velocity dip moveout Artley (1992); Godfrey (1992); Meinardus and Schleicher (1993) undeniably improved the zero-offset stack section. However, one can wonder if they clearly improve the result of the post-stack migrated section.

In this paper I show that the depth-variable velocity dip moveout
strongly differs from the constant-velocity dip moveout not by
the shape of the operator (although the operator is squeezed horizontally
when the velocity increases with depth Artley (1992); Hale (1983))
but by the amplitude distribution along the operator. In the second
section, a synthetic data example shows how the processing flow
NMO-*v*(*z*) DMO-post-stack migration is comparable to pre-stack migration.

11/16/1997