Elimination of the Symmetrical Artifacts in Kirchhoff Depth Migration for 3-D Whole-Space Tunnel Seismic Imaging

Tunnel seismic prediction (TSP) faces challenges in accurately imaging geological anomalies due to the confined spaces of subterranean tunnels in observation, differing markedly from the open spaces encountered in surface seismic exploration. Conventional prestack depth migration approaches, such as Kirchhoff and reverse time migration (RTM), are prone to producing annular artifacts centered on the survey line, as these standard imaging techniques cannot discriminate the propagation direction of reflected waves, imaging them indistinctly onto all possible imaging points. Although previous studies utilizing the polarization attributes of seismic waves can mitigate such symmetrical artifacts to some extent, they fall short of fully suppressing them, particularly for reflectors at small azimuth angles relative to the survey line. This article proposes an innovative solution, whole-space Kirchhoff polarization depth migration (WSKPDM), designed to thoroughly eliminate these migration artifacts. WSKPDM utilizes polarization information extracted from multiple seismic traces to ascertain the true propagation directions of reflected waves, thereby imaging only veritable reflection points. This effectively removes symmetrical artifacts, enhancing the visualization of subsurface geological structure. Testing on synthetic seismic data from diverse fault models and real-world tunnel data shows that WSKPDM surpasses conventional techniques in imaging accuracy. Moreover, WSKPDM demonstrates robust noise immunity even with random noise and reversed polarity in seismic data. With minimal adjustments to account for the distinct polarization directions of S-wave and P-wave, WSKPDM also allows efficient S-wave imaging. This promising WSKPDM method significantly improves the clarity and reliability of TSP imaging, providing a crucial tool for safer and more efficient tunnel construction.