An efficient vector elastic reverse-time migration method in the hybrid time and frequency domains

Vector elastic reverse-time migration is an efficient tool to provide clear subsurface elastic images with correct polarities. However, the decomposition of elastic wavefields into vector P- and S-wavefields is computationally expensive, particularly in heterogeneous and complex anisotropic media. We develop an computationally efficient vector elastic reverse-time migration method in the hybrid time and frequency domains to greatly improve the computational efficiency. This computational efficiency improvement results largely from reducing the high computational cost of qP/qS-wave decomposition in anisotropic media. Rather than decomposing elastic wavefields in the time domain into vector qP and qS wavefields for each time step, we conduct the wavefield decomposition in the frequency domain for a few given frequencies. In general, the number of selected frequencies is much smaller than the number of time steps, leading to greatly reduced computational costs for wavefield decomposition in the frequency domain. We further combine an implicit directional wavefield separation into the vector elastic reverse-time migration to enhance the image quality. Numerical results demonstrate that our new method produces almost identical images for complex models using only approximately ten percent of the computational time of the conventional time-domain method.