Vector P‐ and S‐wave pre‐stack reverse‐time migration for tunnel spaces

Abstract

ABSTRACTMigration is considered to be a key step in the data processing of the seismic advancement predictions of tunnels, and it directly affects the final interpretations. Therefore, with the goal of addressing the limitations of the current acoustic reverse‐time migration processes, as well as deepening the understanding of the interactions between different wave modes in traditional elastic reverse‐time migration, a vector P‐ and S‐wave reverse‐time migration method is proposed in this study. Consideration is given to the actual tunnel spaces, and forward calculations and reverse‐time extrapolations of the wavefields are carried out based on the first‐order velocity‐stress elastic wave equation of P‐ and S‐wave separation and a high‐order staggered‐grid algorithm. The imaging conditions of a source‐normalized cross‐correlation are used to realize the imaging. Then, a Laplace filtering method is adopted to suppress the low‐frequency artefacts. Numerical simulations of the weak interlayer and karst cave models show that the proposed method had the ability to more effectively suppress noise and achieve high‐precision imaging of tunnel spaces, when compared with using horizontal or vertical components to directly obtain the images. The positions and shapes within the tunnel spaces can be accurately imaged regardless of whether they are lithologic interfaces or local geological bodies. This is found to improve the resolution and accuracy of the tunnel advancement predictions. Finally, the proposed method is successfully applied to the real data processing, and the effects are found to be satisfactory.