RTM interpolation using time-shift gathers

Summary We present an approach for increasing imaging resolution of reverse-time migration (RTM) by taking advantage of time-shift gathers. The method has two steps: migrating seismic data with the extended imaging condition to get time-shift gathers and accumulating the time-shift gathers along time-shift axis after they are transformed to zero-lag time-shift by a post-stack depth migration on a finer grid. The final image is generated on a grid which is denser than that of the original time-shift images. The proposed method is based on the observation that non-zero-lag time-shift images recorded by the regular computing grid contain the information of zero-lag time-shift image of a denser grid, and such information can be continued to zero-lag time-shift and refocused at the correct locations on the denser grid. The extra computational amount of the method relative to RTM has the computational cost of zero-offset migration, which is almost negligible when compared to prestack shot-record RTM. Numerical tests on synthetic models demonstrate that the method can effectively improve RTM resolution. It can also improve the efficiency of RTM if the source and receiver wavefield extrapolations are performed on a coarse grid.