Pre-stack processing of seismic reflection data is significantly simpl
ified if the data organization is the same as that in which the data w
ere acquired in the field; that is, in time slices through common-sour
ce gathers. For an impulsive source, the entire processing stream redu
ces to two elements: velocity analysis and reverse-time pre-stack migr
ation. Many of the steps that are applied as independent operations in
standard processing (including demultiplexing, sorting into common-mi
dpoint gathers, elevation corrections, near-surface velocity static co
rrections, first break muting, ground roll removal, and both normal an
d dip move-out corrections) either are eliminated, or are applied impl
icitly during migration. This approach is ideally suited to parallel p
rocessing, and can be implemented in machines with small processor mem
ories.