OFFSET CONTINUATION OF SEISMIC SECTIONS*

Geometrical acoustic and wave theory lead to a second‐order partial differential equation that links seismic sections with different offsets. In this equation a time‐shift term appears that corresponds to normal moveout; a second term, dependent on offset and time only, corrects the moveout of dipping events.

The zero‐offset stacked section can thus be obtained by continuing the section with maximum offset towards zero, and stacking along the way the other common‐offset sections.

Without the correction for dip moveout, the spatial resolution of the section is noticeably impaired, thus limiting the advantages that could be obtained with expensive migration procedures. Trade‐offs exist between multiplicity of coverage, spatial resolution, and signal‐to‐noise; in some cases the spatial resolution on the surface can be doubled and the aliasing noise averaged out.

Velocity analyses carried out on data continued to zero offset show a better resolution and improved discrimination against multiples. For instance, sea‐floor multiples always appear at water velocity, so that their removal is simplified.

This offset continuation can be carried out either in the time‐space domain or in the time‐wave number domain. The methods are applied both to synthetic and real data.