摘要：Most of the wavefield downward continuation migration approaches are relying on one-way wave
equations, which move the seismic energy always in one direction along depth. The one-way
downward continuation migrations only use the primaries for imaging and do not treat secondary
reflections recorded on the surface correctly. In this paper, we investigate wavefield depth
extrapolators based on the full acoustic wave equations, which can propagate wave components to
opposite directions. Several two-way wavefield downward continuation propagators are
numerically tested in this study. Recursively implementing of the depth extrapolator makes it
necessary and important to eliminate the unstable wave modes, that is, evanescent waves. For the
laterally varying velocity media, distinction between the propagating and evanescent wave mode
is less clear. We demonstrate that the spatially localized two-way beamlet propagator is an
effective way to remove the evanescent waves while maintain the propagating mode in laterally
inhomogeneous media.
