Reverse time migration imaging method for tunnel seismic forward‐prospecting in viscoacoustic media

Abstract The imaging of geological structure in front of a tunnel face is conducive to the safe construction of tunnels. The reverse time migration (RTM) method is popular for its high imaging accuracy. However, most of the current tunnel seismic RTM methods assume complete elasticity, ignoring the nature of wave propagation attenuation, resulting in a poor imaging outcome, especially when tunnelling in the shallow subsurface. Thus, it is necessary to study tunnel RTM suitable for attenuating strata. First, considering the frequency of tunnel seismic forward‐prospecting is usually higher than that of ground surface seismic exploration, we established a corresponding tunnel viscous media model to enable viscoacoustic forward modelling of seismic wavefield. Then, a simultaneous compensation approach for its amplitude and phase velocity is proposed based on the combination of the real and imaginary parts of the complex modulus. After the compensation of seismic wavefields, the tunnel Q ‐RTM imaging method in viscoacoustic media is formed, and its effectiveness is verified by numerical examples. Compared with RTM without attenuation compensation, tunnel Q ‐RTM effectively enhances the imaging energy and has higher positioning accuracy, improving the imaging effect of complex structures (especially at larger distances from the tunnel face). In the end, a detailed case study is presented to demonstrat the potential of the proposed method for field application.