Elastic least-squares reverse time migration based on decoupled wave equations

Elastic reverse time migration (ERTM) is developed for bet -ter characterization of complex structures by imaging multi-component seismic data. However, conventional ERTM is subject to limitations such as finite recording aperture, limited bandwidth, and imperfect illumination. Elastic least-squares reverse time migration (ELSRTM) can improve imaging accu-racy gradually with iterations by minimizing the residuals between the observed and calculated multicomponent data. Conventional ELSRTM suffers from crosstalk artifacts caused by coupled elastic wavefields with different wave modes. Decomposing the coupled elastic wavefields into pure P-and S-waves is an effective method to suppress these crosstalk artifacts. Considering the trade-off between calculation accuracy and efficiency, we have developed a new ELSRTM scheme for isotropic media based on decoupled wave equations to suppress these wave mode-related crosstalk artifacts in the images of con-ventional ELSRTM. Pure wavefields are obtained by solving the decoupled wave equations using the finite-difference method in our new ELSRTM method. We also derive new decoupled ad-joint-state wave equations that are suitable for the elastic veloc-ity-stress equations in isotropic media. Furthermore, we use the gradient equations based on pure wavefields to update the reflec-tivity images. Synthetic examples demonstrate that our new ELSRTM method can generate images that better represent the subsurface when compared with conventional ERTM and con-ventional ELSRTM.