3-D Migration to Zero Offset for a Constant Velocity Gradient

DMO processes are designed to move energy to where it would have been recorded by a zero-offset experiment conducted on the datum, For a constant velocity model, the spatial correction is always on a line between the source and the receiver to a position updip from the trace midpoint. and the temporal correction is a shift towards zero time additional to NMO, there being no DMO effects for pure strike shooting. In the case of a non-constant velocity field refraction effects complicate the situation, and the appropriate operator for a given reflection title becomes an areal surface whose characteristics may be counterintuitive; for example, there can be marked "DMO" effects even for strike shooting, with spatial and temporal corrections occurring in a direction opposite to the corrections for dip shooting. In this paper+H182 we derive the MZO (Migration to Zero Offset) operator for a velocity which increases linearly with depth, and we exbibit the surprising and important effects of this operator when applied to data for which the source-receiver orientation is strike to the reflectors.