Evaluation of faults and their effect on ground-water flow southwest of Frenchman Flat, Nye and Clark Counties, Nevada: A Digital Database

Ground-water flow through the region south and west of Frenchman Flat, in the Ash Meadows subbasin of the Death Valley ground-water flow system, is controlled mostly by faults which arrange the distribution of permeable and impermeable rocks. In addition, most permeability is along fractures caused by faulting in carbonate rocks. Large faults are more likely to reach the potentiometric surface as deep as 325 meters below the ground surface and are more likely to effect the flow path than small faults. This study concentrated on identifying large faults, especially where they cut carbonate rocks. Small faults, however, may develop as much permeability as large faults if they are penetrative and are part of an anastomosing fault zone. The overall pattern of faults and joints at the ground surface in the Spotted and Specter Ranges is an indication of the fracture system at the depth of the water table. Most of the faults in these ranges are west-southwest-striking, high-angle faults, 100 to 3,500 meters long, with 10 to 300 meters of displacement. Many of them, such as those in the Spotted Range and Rock Valley are left-lateral strike-slip faults that are conjugate to the NW-striking right-lateral faults of the Las Vegas Valley shear zone. These faults control the ground-water flow path, which runs west-southwest beneath the Spotted Range, Mercury Valley and the Specter Range.
The Specter Range thrust is a significant geologic structure with respect to ground- water flow. This regional thrust fault emplaces siliceous clastic strata into the north central and western parts of the Specter Range. These rocks act as a barrier that confines ground- water flow to the southern part of the range, directing it southwestward toward springs at Ash Meadows. These siliceous clastic aquitard rocks and overlying Cenozoic deposits probably also block westward flow of ground-water in Rock Valley, diverting it southward to the flow path beneath the southern part of the Specter Range.

位于死亡谷地下水流系统（Death Valley ground-water flow system）的阿什梅多斯次盆地（Ash Meadows subbasin）内，法国人平地（Frenchman Flat）以南及西侧区域的地下水流，主要受调控透水与不透水岩层分布的断层控制。此外，绝大多数透水通道均赋存于碳酸盐岩（carbonate rocks）因断裂活动形成的裂隙中。大型断层更易抵达地表以下深达325米的测压水头面（potentiometric surface），且相较于小型断层，其对地下水流路径的影响更为显著。本研究重点开展大型断层的识别工作，尤其关注切穿碳酸盐岩的大型断层。然而，若小型断层具有贯穿性且属于网状断裂带（anastomosing fault zone）的组成部分，其所能提供的透水性能可与大型断层相当。斑点山脉（Spotted Range）与幽灵山脉（Specter Range）地表出露的断层与节理整体格局，可反映地下水位埋深处的裂隙系统特征。这些区域内的多数断层均为走向西南西的高角度断层，长度介于100至3500米之间，断距为10至300米。其中诸多断层（如斑点山脉与罗克谷（Rock Valley）内的断层）均为左旋走滑断层（left-lateral strike-slip faults），与拉斯维加斯谷剪切带（Las Vegas Valley shear zone）内的北西向右旋走滑断层形成共轭关系。这些断层调控着地下水流路径，该路径自斑点山脉、水星谷（Mercury Valley）及幽灵山脉下方以西南西方向延伸。
幽灵山脉逆冲断层（Specter Range thrust）是影响地下水流的重要地质构造。该区域性逆冲断层将硅质碎屑岩层（siliceous clastic strata）推覆至幽灵山脉的中北部与西部区域。这些岩层构成了隔水屏障，将地下水流限制在山脉南部，并引导其向西南方向流向阿什梅多斯的泉群。这些硅质碎屑弱透水层（siliceous clastic aquitard）及其上覆的新生代沉积物（Cenozoic deposits），大概率同样阻滞了罗克谷内的地下水向西流动，使其改道向南，流向幽灵山脉南部下方的地下水流路径。