The safety and efficiency of tunnel construction depend on the knowledge of complex geologic conditions. Hence, an accurate forward-prospecting technique is required to detect unexpected inhomogeneous geologic structures ahead of tunnel construction. As an accurate method to image geologic heterogeneities, elastic reverse time migration (ERTM) is introduced to the field of tunnel forward prospecting. However, in the tunnel environment, ERTM images may suffer from the interference of crosstalk artifacts, which are caused by converted waves on tunnel surfaces. Therefore, considering the actual influence of the tunnel body, the decoupled nonconversion elastic equation was incorporated into traditional ERTM. This method prevents the generation of converted waves but ensures independent P- and S-wave propagation. In addition, wave-mode separation for raw seismic data is required in our approach. Synthetic examples based on the real geologic environment of tunnels show that our method produces satisfactory results for P-wave and S-wave imaging and the S-wave can produce a better imaging effect in tunnels. Finally, we apply our method to the seismic data obtained from a real highway tunnel construction site to demonstrate its performance in real-world applications. The results indicate that the migrated images can help to accurately constrain the geologic formations ahead of the tunnel face.

中文翻译：

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基于解耦非转换弹性波方程的隧道叠前逆时成像

隧道施工的安全性和效率取决于对复杂地质条件的了解。因此，需要一种精确的前向勘探技术来在隧道施工之前检测出意想不到的不均匀地质构造。作为对地质异质性进行成像的一种准确方法，弹性逆时偏移（ERTM）被引入到隧道正向勘探领域。但是，在隧道环境中，ERTM图像可能会受到串扰伪像的干扰，这是由隧道表面上的转换波引起的。因此，考虑到隧道主体的实际影响，将解耦的非转换弹性方程式合并到传统的ERTM中。这种方法可以防止产生转换波，但可以确保独立的P波和S波传播。此外，在我们的方法中，需要对原始地震数据进行波模式分离。根据隧道真实地质环境的综合算例表明，我们的方法在P波和S波成像中均取得了令人满意的结果，而S波在隧道中的成像效果更好。最后，我们将我们的方法应用于从实际公路隧道施工现场获得的地震数据，以证明其在实际应用中的性能。结果表明，迁移的影像可以帮助准确地约束隧道面前方的地质构造。我们将我们的方法应用于从实际公路隧道施工现场获得的地震数据，以证明其在实际应用中的性能。结果表明，迁移的影像可以帮助准确地约束隧道面前方的地质构造。我们将我们的方法应用于从实际公路隧道施工现场获得的地震数据，以证明其在实际应用中的性能。结果表明，迁移的影像可以帮助准确地约束隧道面前方的地质构造。