Implementation of prestack reverse time migration using frequency-domain extrapolation

We implement prestack reverse time migration (RTM) using frequency-domain extrapolation. We assume the observed data are the scattered field from the seismic experiment; then we time reverse them and derive the corresponding multipoint virtual sources to place along the receiver line rather than treat them as boundary conditions, which are common in time-domain reverse time migration (TRTM). Because the number of virtual sources is equal to the number of independent true sources in prestack frequency-domain reverse-time migration (FRTM), wavefield extrapolation is efficient in the frequency domain using a direct lower/upper (LU) triangular solver for 2D solutions and is still feasible using a parallel iterative or hybrid direct/iterative solver for 3D solutions. Each frequency implicitly contains information for all times, so we can implement the excitation-time and crosscorrelation imaging conditions straightforwardly without disk storage or input/output (I/O). Comparing costs, prestack shot-record FRTM is competitive with prestack shot-record TRTM. In our tests, prestack acoustic-wave FRTM accurately recovers the correct images of subsurface reflectors using 2D synthetic data.