Migration before stack—Procedure and significance

Abstract

Common‐depth‐point (CDP) stacking is based on the assumption that reflection points are coincident and situated midway between the respective source and receiver locations. If the reflector is structurally deformed, the reflection points move updip from the midpoint. As the structural dip increases, the reflection points for a CDP group of traces are farther removed from each other and normal stacking procedures [i.e., reflection apparent velocities for horizontal reflectors used for normal moveout (NMO) corrections] become increasingly inaccurate. Under such circumstances prestack migration is desirable, particularly when high frequencies are to be preserved. One published approach to prestack migration (Sattlegger and Stiller, 1973) involves the generation of substacks of adjacent traces followed by migration and summation of individual substacks. While adequate in many instances, cases exist where even substacks are degraded by the reflection time differential between component traces. This paper discusses an alternative technique to prestack migration without recourse to substacks. Common‐source traces, after gain recovery and static time corrections but before NMO corrections, are migrated using Kirchhoff summation. Aperture is computed for each sample according to specified maximum dips. Traces are simultaneously migrated and stacked, then output sequentially in sets of 12. The method is economical and provides enhanced reflection continuity and reliability in comparison to poststack migration. Moreover, the collapsing of diffractions is more effective.

An iterative inversion of back‐scattered acoustic waves

“…The crosscorrelation is then weighted by the appropriate coefficient (amplitude factor for geometrical spreading and ang!Jlar factor) and added to the array representing the parameter at the current point of the model space. This first iteration of the inversion procedure is very similar to a pres tack Kirchhoff migration (Jain and Wren, 1980 which are computed only once at the beginning of the inversion procedure. In our case, this choice of tJ 0 means a larger initial computational effort to estimate that preconditioning matrix.…”

Interpretation of ambiguous reflection data by imaging processes: An example profile crossing steep submarine valley at the sea bottom

“…This method simplifies the task of inverting an elastic wave field for an image of the earth through which it has propagated (Le . It is based mainly on three assumptions that reduce the inversion of reflection data to a process similar to the Kirchhoff sum migration of Jain and Wren (1980). The method requires travel time curves to be computed from a velocity model as a velocity input.…”

Focusing in Prestack Isochrone Migration Using Instantaneous Slowness Information

“…JAIN and WREN (1980) suggested a combination of Kirchhoff migration and likelihood weighting to improve the signal-to-noise ratio of common shot migration schemes. JAIN and WREN (1980) suggested a combination of Kirchhoff migration and likelihood weighting to improve the signal-to-noise ratio of common shot migration schemes.…”