Decoupled elastic least-squares reverse time migration and its application in tunnel geologic forward prospecting
Bin Liu, Jiansen Wang, Yuxiao Ren, Xu Guo, Lei Chen, Lanbo Liu
Abstract
ABSTRACT Accurate seismic imaging can ensure safe and efficient tunnel construction under complex geologic conditions. As a high-precision migration method, reverse time migration (RTM) has been introduced into tunnel seismic forward prospecting. However, the resolution of traditional RTM imaging results may not meet the requirements in a complex tunnel environment, which affects the interpretation of tunnel seismic forward-prospecting results. We have developed a least-squares RTM method based on the decoupled elastic wave equation in tunnels. The Born forward-modeling operator and its exact adjoint migration imaging operator are derived to ensure a stable convergence of the conjugate-gradient method. Moreover, a pseudo-Hessian-based preconditioning operator is adopted to accelerate the convergence. Numerical examples are provided to verify the efficiency of our scheme. A field test in a traffic tunnel construction site is performed to show the good application effect of the decoupled elastic least-squares RTM in practical situations.