1. The extra area around the area to be surveyed that must be covered because of the inward movement of dipping reflections and focusing of seismic amplitude dispersed over Fresnel zones during 3-D migration. Often referred to as a migration fringe or migration halo. 2. The portion of imaged area where coverage is not uniform because of differences in multiplicity, offset or azimuth mixes, or other factors that lessen confidence in data comparisons.