Seismic data processing method

A method for migrating seismic data is disclosed in which seismic traces recorded by a plurality of receivers are separated into offset bands according to the offsets of the traces. The data in each offset band is then migrated according to a downward continuation method. The downward continuation method includes the calculation of a constant that is not dependent on the value of the wave field. The constant is used to calculated the wave field for all offset bands for a given z level, thereby reducing time and computation resources consumed by the migration of the offset bands. Following the downward continuation, an imaging condition may be applied to produce a seismic image.