Earth and Environmental Science Department, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM, 87801, USA.
HydroResolutions, 321 Fisher St., Socorro, NM, 87801, USA.
Ground Water. 2021 May;59(3):396-409. doi: 10.1111/gwat.13062. Epub 2020 Dec 24.
Fault zones are an important control on fluid flow, affecting groundwater supply, contaminant migration, and carbon storage. However, most models of fault seal do not consider fault zone cementation, despite the recognition that it is common and can dramatically reduce permeability. In order to study the field-scale hydrogeologic effects of fault zone cementation, we conducted a series of aquifer pumping tests in wells installed within tens of meters of the variably cemented Loma Blanca Fault, a normal fault in the Rio Grande Rift. In the southern half of the study area, the fault zone is cemented by calcite; the cemented zone is 2-8 m wide. In the center of the study area, the cemented fault zone is truncated at a buttress unconformity that laterally separates hydrostratigraphic units with a ∼40X difference in permeability. The fault zone north of the unconformity is not cemented. Constant rate pumping tests indicate that where the fault is cemented, it is a barrier to groundwater flow. This is an important demonstration that a fault with no clay in its core and similar sediment on both sides can be a barrier to groundwater flow by virtue of its cementation; most conceptual models for the hydrogeology of faults would predict that it would not be a barrier to groundwater flow. Additionally, the lateral permeability heterogeneity across the unconformity imposes another important control on the local flow field. This permeability discontinuity acts as either a no-flow boundary or a constant head boundary, depending on the location of pumping.
断裂带是控制流体流动的重要因素，影响地下水供应、污染物迁移和碳储存。然而，大多数断裂密封模型都没有考虑断裂带胶结作用，尽管人们已经认识到这种作用很常见，并可能显著降低渗透率。为了研究断裂带胶结作用对场地尺度水文地质的影响，我们在距离洛马布兰卡断裂(Loma Blanca Fault)数十米的两口井中进行了一系列含水层抽水试验，该断裂是里奥格兰德裂谷中的一条正断层。在研究区的南部，断裂带被方解石胶结；胶结带宽 2-8 米。在研究区中心，胶结断裂带在一个支撑不整合面处被截断，该不整合面将渗透率相差约 40 倍的水文地层单元横向分隔开来。不整合面以北的断裂带未胶结。定流量抽水试验表明，在断裂带胶结的地方，它是地下水流动的屏障。这有力地证明了即使断裂带核心没有粘土，两侧的沉积物相似，也可以通过胶结作用成为地下水流动的屏障；大多数关于断裂带水文地质学的概念模型预测它不会成为地下水流动的屏障。此外，不整合面两侧的渗透率非均质性对局部流场施加了另一个重要控制。这种渗透率不连续性可作为无流动边界或恒定水头边界，具体取决于抽水位置。
