LAYER-STRIPPING REVERSE-TIME MIGRATION

We present a layer-stripping method of migration for irregularly layer ed media in which first-order velocity discontinuities separate region s of constant or smoothly varying velocity. We use the reverse-time me thod to migrate seismic data layer by layer, from the surface downward s. As part of the migration of a given layer, the bottom boundary of t he layer is defined based on power in the migrated signal, and a seism ic section is collected along it. This new section serves as the bound ary condition for migration in the next layer. This procedure is repea ted for each layer, with the final image formed from the individual la yer images. Layer-stripping migration consists of three steps: (1) lay er definition, (2) wavefield extrapolation and imaging, and (3) bounda ry determination. The migration scheme when used with reverse-time ext rapolation is similar to datuming with an imaging condition. The rever se-time method uses an explicit fourth-order time, tenth-order space, finite-difference approximation to the scalar wave equation. The advan tages of layer-stripping reverse-time migration are: (1) it preserves the benefits of the reverse-time method by handling strong velocity co ntrasts between layers and steeply dipping structures; (2) it reduces computer memory and saves computation time in high-velocity layers, an d (3) it allows interpretational control of the image. Post-stack laye r-stripping reverse-time migration is illustrated with a synthetic CMP data example. Prestack migration is illustrated with a synthetic data set and with a marine seismic reflection profile across the Santa Mar ia Basin and the Hosgri Fault in central California.