Decoupled elastic least-squares reverse time migration and its application in tunnel geologic forward prospecting

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.