Anisotropic Least Squares Reverse Time Migration of Target Region Based on Marchenko Double-Focusing

Target-oriented least squares reverse time migration (TO-LSRTM) is a method designed for imaging below the complex overburden. It achieves this by bypassing the overburden and focusing wavefields over the region of interest. The critical aspect of this process lies in obtaining Marchenko double-focusing redatumed data. However, traditional Marchenko redatuming methods neglect the impact of anisotropy, leading to distortions in the travel times and amplitudes of redatumed data, thus affecting imaging accuracy. To overcome this problem, we develop a target-oriented vertical transverse isotropic least-squares reverse time migration (TO-VTI-LSRTM) method. This method uses the direct wave from the subsurface virtual source point obtained by the first-order VTI pseudo-acoustic equation as the initial condition to solve the Marchenko equation, so as to correct the velocity anisotropy in the process of redatuming, and the redatumed data is used as the virtual observed data for inversing the reflection coefficients of the subsurface local region. Numerical experiments validate the capabilities and advantages of the proposed method. Imaging results demonstrate that this approach effectively eliminates imaging artifacts caused by anisotropy and overburden internal multiple reflections, resulting in high-quality imaging results.