We have combined electrical resistivity tomography (ERT), geologic information from boreholes and outcrops, and hydrogeologic data to investigate field-scale fault-zone cementation of the Loma Blanca Fault in the Rio Grande Rift. We have collected electrical resistivity data from 16 transects and geologic samples from 29 boreholes (completed as groundwater wells to 30 m depth) across and around the fault. The 2D ERT profiles, whose interpretations are constrained by geologic data, indicate (1) a high resistivity zone in cemented portions of the fault below the water table and (2) in the unsaturated zone, a low-resistivity feature along the cemented portions of the fault. The high-resistivity zone below the water table is consistent with a 10% reduction in porosity due to the fault zone cementation. With the same porosity in the unsaturated zone, the low-resistivity feature in the cemented fault zone is consistent with saturation >0.7, in contrast to saturation 0.2–0.7 for sediment outside of the cemented fault zone. In addition, subsurface samples and ERT profiles delineate a buttress unconformity (i.e., steeply dipping erosional contact) corresponding to a paleovalley margin. This unconformity truncates the cemented fault zone and separates Pliocene axial-fluvial sand (deposited by an ancestral Rio Grande) from late Quaternary sand and gravel (deposited by the Rio Salado, a Rio Grande tributary). The cemented fault zone in the southern portion of the study area is a hydrogeologic barrier; north of the buttress unconformity, where the cemented fault zone has been removed by erosion, the fault is not a hydrogeologic barrier. The integration of geologic, geophysical, and hydrogeologic observations is key to developing our understanding of this complex system, and it allows us to demonstrate the utility of ERT in detecting subsurface fault-zone cementation.

中文翻译：

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使用电阻率检测断层带特征和古卵切口：新墨西哥州洛马布兰卡断层

我们将电阻率层析成像（ERT），钻孔和露头的地质信息以及水文地质数据相结合，以研究里奥格兰德大裂谷Loma Blanca断层的田间规模断层带胶结作用。我们从断层上和断层附近的16个样点收集了电阻率数据，并从29个钻孔（已完成至30m深度的地下水井中）收集了地质样品。二维ERT剖面的解释受地质数据的约束，表明（1）地下水位以下断层胶结部分的高电阻率区和（2）在非饱和区中的沿岩层胶结部分的低电阻率特征错误。由于断层带胶结作用，地下水位以下的高电阻率带与孔隙率降低了10％一致。在非饱和区孔隙率相同的情况下，胶结断层带的低电阻率特征与饱和度> 0.7一致，而胶结断层带以外的沉积物的饱和度为0.2-0.7。另外，地下样品和ERT剖面描述了对应于古卵缘的支撑不整合面（即陡倾侵蚀接触）。这种不整合面将胶结断层带截断，并将上新世的轴向河床砂（由祖先的里奥格兰德沉积）与第四纪晚期的砂砾和砾石（由里奥萨拉多（Rio Salado，里奥格兰德支流沉积）沉积）分开。研究区南部的胶结断层带是水文地质屏障。在支撑不整合面以北，胶结断层带已被侵蚀除去的情况下，该断层不是水文地质屏障。地质，地球物理，