Least-squares based rectangular-grid cross and rhombus stencils for acoustic wave propagation and reverse time migration

Recent researches on migration focus on computational efficiency and imaging accuracy. Modeling is at the heart of the reverse time migration (RTM), a powerful tool for imaging geologically complex structures, and controls its efficiency and accuracy. Finite-difference (FD) method is widely used in modeling. Though the rhombus stencil FD scheme has high accuracy, it is expensive and only applicable to square grids. In order to make the high-accuracy FD scheme more efficient and flexible, we develop a rectangle-grid cross and rhombus stencils FD scheme (RCR). To further improve accuracy, the optimal FD method based on least squares (LS) is introduced into the RCR. Correspondingly, the absorbing boundary condition (ABC) should be extended to rectangular grids for suppressing the boundary reflections of modeling, we therefore develop the rectangular-grid hybrid ABC. To obtain high-efficiency and high-accuracy RTM images, the adaptive variable-length spatial operators scheme is combined with the LS-based RCR when implementing the wavefield extrapolation, and the efficient boundary condition is adopted when performed on GPU card. By comparing the RCR with the rectangular-grid on cross stencil FD scheme (RC) in terms of their phase dispersion, stability and snapshot, we demonstrate the superiority of the LS-based RCR. We have also proven the effectiveness of the rectangular-grid hybrid ABC on absorption, and shown that under the similar accuracy, the RCR-based RTM can achieve higher efficiency than the RC-based one by adopting a larger time interval. Finally, the RCR-based RTM obtains a well-imaged profile for field data. (C) 2019 Elsevier Inc. All rights reserved.