Layer‐stripping reverse‐time migration1

Abstract

AbstractWe present a layer‐stripping method of migration for irregularly layered media in which first‐order velocity discontinuities separate regions of constant or smoothly varying velocity. We use the reverse‐time method to migrate seismic data layer by layer, from the surface downwards. As part of the migration of a given layer, the bottom boundary of the layer is defined based on power in the migrated signal, and a seismic section is collected along it. This new section serves as the boundary condition for migration in the next layer. This procedure is repeated for each layer, with the final image formed from the individual layer images. Layer‐stripping migration consists of three steps: (1) layer definition, (2) wavefield extrapolation and imaging, and (3) boundary determination. The migration scheme when used with reverse‐time extrapolation is similar to datuming with an imaging condition. The reverse‐time method uses an explicit fourth‐order time, tenth‐order space, finite‐difference approximation to the scalar wave equation.The advantages of layer‐stripping reverse‐time migration are: (1) it preserves the benefits of the reverse‐time method by handling strong velocity contrasts between layers and steeply dipping structures; (2) it reduces computer memory and saves computation time in high‐velocity layers, and (3) it allows interpretational control of the image.Post‐stack layer‐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 Maria Basin and the Hosgri Fault in central California.