Critical Zone Structure by Elastic Full Waveform Inversion of Seismic Refractions in a Sandstone Catchment, Central Pennsylvania, USA
Critical Zone Structure by Elastic Full Waveform Inversion of Seismic Refractions in a Sandstone Catchment, Central Pennsylvania, USA
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DOI：
10.1029/2021jb023321
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发表时间：
2022-02
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通讯作者：
Xuejian Liu;T. Zhu;J. Hayes
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作者：
Xuejian Liu;T. Zhu;J. Hayes
地震成像为揭示地球临界区(CZ)内的构造和量化地下流体性质提供了关键信息。由地震折射层析成像或声波全波形反演(FWI)估计的P波速度(Vp)模型可用于圈定CZ地区风化基岩的厚度，但对流体性质的映射却不明确。考虑到S波对地下流体饱和度的互补敏感性，我们探索了一种改进的弹性全波形反演方法来同时估计VP和S波速度模型。我们提出了几种策略来稳健地实现有噪的单(垂直)分量折射数据的EFWI：(A)我们对地震数据进行加窗以保留主要包括P波、转换波和S波折射的早期到达；(B)我们使用相关失配而不是经典的L2失配来减少不可靠数据幅度的干扰；以及(C)我们使用多尺度频率策略和迭代约束进行反演，并遵循VP/VS>；1规则。我们验证了EFWI方法利用合成数据可靠地重建VP和VS模型。然后，我们将我们的EFWI方法应用于在Susquehanna页岩山临界区观测站的Garner Run站点获得的地震折射数据。倒置的Vp和VS模型指示了三个不同的层，并且具有显著的横向和深度非均质性(例如，低Vp和VS带)。结合岩石物理知识对Vp、Vs和Vp/Vs进行联合分析，揭示了潜在的气或水聚集区。
Seismic imaging provides key information for revealing structures within Earth's critical zone (CZ) and quantifying subsurface fluid properties. The P‐wave velocity (Vp) models estimated by seismic refraction tomography or acoustic full waveform inversion (FWI) are useful to delineate the thicknesses of weathered bedrock but ambiguously map fluid properties in CZ. Considering the complementary sensitivity of S‐wave to subsurface fluid saturation, we explore advanced elastic full waveform inversion (EFWI) to estimate both Vp and S‐wave velocity (Vs) models simultaneously. Several strategies are proposed for robust EFWI implementation of noisy single (vertical) component refraction data: (a) we window seismic data to preserve early arrivals mainly including P‐wave, converted waves, and S‐wave refractions; (b) we use a correlative misfit rather than the classic L2 misfit to alleviate the interference of unreliable data amplitudes; and (c) we perform inversion using a multiscale frequency strategy with the iterative constraint with the rule of Vp/Vs > 1. We validate that the EFWI approach reliably reconstructs Vp and Vs models using synthetic data. Then, we apply our EFWI approach to seismic refraction data acquired at the Garner Run site of the Susquehanna Shale Hills Critical Zone Observatory. The inverted Vp and Vs models indicate three distinguished layers and with significant lateral and depth heterogeneities (e.g., low Vp and Vs zones). Joint analyses of Vp, Vs, and Vp/Vs with rock‐physics knowledge reveal potential gas or water gathering zones.