Imaging overturned waves by plane-wave migration in tilted coordinates

Guojian Shan and Biondo Biondi

shan@sep.stanford.edu, biondo@sep.stanford.edu

ABSTRACT

We image overturned waves by decomposing the source and receiver wavefields into plane-waves. For each plane-wave, we extrapolate the source and receiver wavefields in a tilted coordinate system and cross-correlate them to obtain Common Image Gathers (CIGs). The tilting angle for the coordinate system is determined by the propagation direction of the plane wave. In tilted coordinates, the propagation direction is close to the extrapolation direction, so we can image steeply dipping reflectors and overturned waves with the one-way wave equation. We can also obtain robust, dip-dependent angle-domain CIGs (ADCIGs) by the same method employed in reverse-time migration. These gathers provide moveout information and thus are very important for velocity analysis on steeply dipping reflectors. Since plane-wave migration needs no padding and the extrapolation is one-way wave equation based, our method is very efficient. We demonstrate our method on the Marmousi model by computing the Green's function for a point source on the surface. We also apply our method to a North Sea real dataset with overturned events.