The Rock Valley fault zone (RVFZ), an intraplate strike‐slip fault zone in the southern Nevada National Security Site (NNSS), hosted a series of very shallow (<3 km) earthquakes in 1993. The RVFZ may also have hydrological significance within the NNSS, potentially playing a role in regional groundwater flow, but there is a lack of local hydrological data. In the Spring of 2021, we collected active‐source accelerated weight drop seismic data over part of the RVFZ to better characterize the shallow subsurface. We manually picked ∼17,000 P‐wave travel times and over 14,000 S‐wave travel times, which were inverted for P‐wave velocity (⁠VP⁠), S‐wave velocity (⁠VS⁠), and VP/VS ratio in a 3D joint tomographic inversion scheme. Seismic velocities are imaged as deep as ∼700 m in areas and generally align with geologic and structural expectations. VP and VS are relatively reduced near mapped and inferred faults, with the most prominent lower VP and VS zone around the densest collection of faults. We image VP/VS ratios ranging from ∼1.5 to ∼2.4, the extremes of which occur at a depth of ∼100 m and are juxtaposed across a fault. One possible interpretation of the imaged seismic velocities is enhanced fault damage near the densest collection of faults with relatively higher porosity and/or crack density at ∼100 m depth, with patches of semiperched groundwater present in the sedimentary rock in higher VP/VS areas and drier rock in lower VP/VS areas. A relatively higher VP/VS area beneath the densest faults persists at depth, which suggests percolation of groundwater via the fault damage zone to the regionally connected lower carbonate aquifer. Potentially, the presence and movement of groundwater may have played a role in the 1993 earthquake aftershocks.

中文翻译：

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走滑断层带的水文影响：来自岩谷联合 3D 体波层析成像的见解

岩谷断层带 (RVFZ) 是内华达州国家安全站点 (NNSS) 南部的板内走滑断层带，1993 年发生了一系列极浅层（<3 公里）地震。RVFZ 也可能具有水文意义。 NNSS 可能对区域地下水流发挥作用，但缺乏当地水文数据。 2021 年春季，我们在 RVFZ 部分区域收集了主动源加速重降地震数据，以更好地表征浅层地下。我们手动选取约 17,000 个 P 波传播时间和超过 14,000 个 S 波传播时间，将其反演为 P 波速度 (⁠VP⁠)、S 波速度 (⁠VS⁠) 和 VP/VS 比率3D联合层析反演方案。地震速度在深达 700 m 的区域成像，通常与地质和结构预期一致。在绘制和推测的断层附近，VP 和 VS 相对减少，在最密集的断层周围，VP 和 VS 下部区域最为突出。我们对 VP/VS 比率进行成像，范围为 ∼1.5 到 ∼2.4，其极值发生在 ∼100 m 的深度，并且并列跨越断层。对成像地震速度的一种可能解释是，在约 100 m 深度具有相对较高孔隙度和/或裂缝密度的最密集断层集合附近，断层损害增强，在较高 VP/VS 区域的沉积岩中存在半栖息地下水斑块， VP/VS 较低区域的岩石较干燥。最密集断层下方存在相对较高的 VP/VS 区域，这表明地下水通过断层破坏带渗透到区域相连的下部碳酸盐含水层。地下水的存在和运动可能在 1993 年地震余震中发挥了作用。