Acoustic and Elastic Reverse-Time Migration With an Angle-Related Imaging Condition for Imaging Steeply-Dipping Structures

The subsurface steeply-dipping structures, such as buried hills, fault zones, and salt flanks, are difficult to accurately image in seismic exploration due to weak illumination from large incident angles. To mitigate this issue, we propose an angle-related imaging condition for acoustic and elastic reverse-time migration (ERTM) to improve the image quality of steeply-dipping structures. We first use the wavefield decomposition method based on the Hilbert transform to decompose the extrapolated wavefield into up–down-left–right going components. We observed that the left- and right-going wavefields can accurately image steeply-dipping structures, while the up- and down-going wavefields mainly contribute to the layers with small dipping angles. Then, an angle-related imaging condition is developed to use the decomposed directional wavefields to enhance the image quality of both flat layers and steeply-dipping structures. In ERTM, after the directional wavefield decomposition, the vector Helmholtz decomposition is used to decouple PS waves to produce PP and PS images. Numerical examples demonstrate that the proposed method produces more accurate images than conventional RTM for steeply-dipping structures.