Increasing deployment of dense arrays has facilitated detailed structure imaging for tectonic investigation, hazard assessment and resource exploration. Strong velocity heterogeneity and topographic changes have to be considered during passive source imaging. However, it is quite challenging for ray-based methods, such as Kirchhoff migration or the widely used teleseismic receiver function, to handle these problems. In this study, we propose a 3-D passive source reverse time migration strategy based on the spectral element method. It is realized by decomposing the time reversal full elastic wavefield into amplitude-preserved vector P and S wavefields by solving the corresponding weak-form solutions, followed by a dot-product imaging condition to get images for the subsurface structures. It enables us to use regional 3-D migration velocity models and take topographic variations into account, helping us to locate reflectors at more accurate positions than traditional 1-D model-based methods, like teleseismic receiver functions. Two synthetic tests are used to demonstrate the advantages of the proposed method to handle topographic variations and complex velocity heterogeneities. Furthermore, applications to the Laramie array data using both teleseismic P and S waves enable us to identify several south-dipping structures beneath the Laramie basin in southeast Wyoming, which are interpreted as the Cheyenne Belt suture zone and agree with, and improve upon previous geological interpretations.

中文翻译：

---

基于谱元法的无源源逆时偏移


密集阵列部署的增加促进了构造调查、灾害评估和资源勘探的详细结构成像。在被动源成像过程中，必须考虑强烈的速度异质性和地形变化。然而，对于基于射线的方法，例如基尔霍夫迁移或广泛使用的远震接收器功能，要处理这些问题是相当具有挑战性的。在本研究中，我们提出了一种基于光谱元法的三维无源源逆时偏移策略。它是通过求解相应的弱形式解，将时间反转全弹性波场分解为振幅守恒矢量 P 和 S 波场，然后是点积成像条件以获得地下结构的图像来实现的。它使我们能够使用区域三维迁移速度模型并考虑地形变化，帮助我们将反射体定位在比传统的基于一维模型的方法（如远震接收器功能）更准确的位置。使用两种综合测试来证明所提出的方法在处理地形变化和复杂速度异质性方面的优势。此外，使用遥震 P 波和 S 波应用于 Laramie 阵列数据，使我们能够识别怀俄明州东南部 Laramie 盆地下方的几个南倾结构，这些结构被解释为夏延带缝合带，并与以前的地质解释一致并进行了改进。