For decades, seismic imaging methods have been used to study the critical zone, Earth's thin, life-supporting skin. The vast majority of critical zone seismic studies use traveltime tomography, which poorly resolves heterogeneity at many scales relevant to near-surface processes, therefore limiting progress in critical zone science. Full-waveform tomography can overcome this limitation by leveraging more seismic data and enhancing the resolution of geophysical imaging. In this study, we apply 2D full-waveform tomography to match the phases of observed seismograms and elucidate previously undetected heterogeneity in the critical zone at a well-studied catchment in the Laramie Range, Wyoming. In contrast to traveltime tomograms from the same data set, our results show variations in depth to bedrock ranging from 5 to 60 m over lateral scales of just tens of meters and image steep low-velocity anomalies suggesting hydrologic pathways into the deep critical zone. Our results also show that areas with thick fractured bedrock layers correspond to zones of slightly lower velocities in the deep bedrock, while zones of high bedrock velocity correspond to sharp vertical transitions from bedrock to saprolite. By corroborating these findings with borehole imagery, we hypothesize that lateral changes in bedrock fracture density majorly impact critical zone architecture. Borehole data also show that our full-waveform tomography results agree significantly better with velocity logs than previously published traveltime tomography models. Full-waveform tomography thus appears unprecedentedly capable of imaging the spatially complex porosity structure crucial to critical zone hydrology and processes.

中文翻译：

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二维近地表全波形断层扫描揭示了关键区域架构的基岩控制

几十年来，地震成像方法一直被用来研究关键区域，即地球薄薄的、支持生命的皮肤。绝大多数关键带地震研究都使用走时层析成像技术，它很难解决与近地表过程相关的许多尺度的异质性，因此限制了关键带科学的进展。全波形断层扫描可以通过利用更多地震数据并提高地球物理成像的分辨率来克服这一限制。在这项研究中，我们应用二维全波形断层扫描来匹配观测到的地震图的相位，并阐明怀俄明州拉勒米山脉一个经过充分研究的流域的关键区域中以前未检测到的异质性。与同一数据集的走时断层图相比，我们的结果显示，在数十米的横向尺度上，基岩深度的变化范围为 5 至 60 m，并且图像陡峭的低速异常表明了进入深层关键区域的水文路径。我们的结果还表明，具有厚裂隙基岩层的区域对应于深层基岩中速度稍低的区域，而高基岩速度区域对应于从基岩到腐泥土的急剧垂直过渡。通过用钻孔图像证实这些发现，我们假设基岩裂缝密度的横向变化主要影响关键区域的结构。钻孔数据还表明，与之前发布的走时断层扫描模型相比，我们的全波形断层扫描结果与速度测井的一致性明显更好。因此，全波形断层扫描似乎前所未有地能够对对关键区域水文和过程至关重要的空间复杂孔隙结构进行成像。