Integrated Structural and Hydrologic Charactrization of Fault Zone Permeability at Well Field to Regional Scales

目前对区域尺度上断裂带渗透率的认识是有限的。特别是，断层间的渗透率测量很少。然而，有明确的迹象表明，在这个尺度下，断层对各种地质过程都有很大的水文地质影响，这可以从不同的水头梯度、断层间的地球化学和地热异常中得到证明。断层带的大尺度渗透性及其对含水层的影响还存在一些具有科学基础和实践意义的问题。例如，如何最好地整合地质和水文信息来有效地约束区域尺度的断层渗透率？虽然现有的小尺度断层渗透率知识在科学上是不可或缺的，但最终，为了解决与水资源管理和地壳中流体、溶质和能量的输送有关的问题，概念和数值模型需要的是区域尺度的渗透率。本研究的科学目标是在野外构造观测、水文地质测试以及概念和数值模拟解释的约束下，在井场区域尺度上表征断裂带渗透率。其基本假设是，通过跨断层含水层测试可以观察到断层周围独特的水文地质响应，通过综合了解露头结构特征、主岩钻孔资料和多尺度水文地质测试可以建立断裂带渗透率特征。以科罗拉多州Elkhorn逆冲断层为现场，研究计划包括以下内容：(1)表征断裂带的地质和内部结构，以更好地了解不同岩性并置对断裂带水文地质性质的影响；(2)在断裂带上钻取新的钻孔并取芯，以获得断裂带渗透率的直接现场观测；(3)在新孔和已有孔中进行跨断层抽水试验，以提供急需的断裂带渗透率的直接测量。(4)通过综合地质、水文地质和地球物理野外资料的数值模拟，建立断裂带渗透率模型。认识到智力价值的三个方面。首先，将地质观测与水文地质测试资料紧密结合，为断裂带渗透率的表征开辟了新的方向。其次，这项研究提供了一个机会，可以深入了解一种常见但研究不足的特殊断层类型——在区域盆地尺度上具有结晶上盘和沉积下盘的逆冲断层。最后，本研究计划的跨断层渗透率测试与地质表征相结合，将通过提供急需的现场测量数据，在断层相关渗透率表征方面取得重大进展。除了培养研究生和为美国西部更好的地下水资源管理做出贡献外，这项拟议研究的更广泛影响的主要方面是增强本科生在水文地质学方面的经验。这项研究将使一大批本科生受益。本科生将参与该项目的所有阶段。实现这一承诺的具体途径包括：(1)招收优秀本科生撰写荣誉论文；(2)与高年级水文地质学课程相关的实地练习。可将地下水位测绘和含水层测试纳入班级相关活动。(3)协调钻孔，以便学生观察作业。最后，两位pi计划共同教授一门两周两学分的夏季本科生野外水文地质学课程。该研究将为该实地课程的许多不同项目提供一个良好的场所，并有助于该计划的实现。

0610027GECurrent understanding of fault-zone permeability at regional scales is limited. Particularly,permeability measurements across faults are scarce. Yet, there are clear indications that faultshave large hydrogeologic impacts on various geologic processes at this scale, as evidenced byvariable hydraulic head gradients, geochemical and geothermal anomalies across faults. Thereremain questions that are scientifically fundamental and practically significant regarding largescalepermeability of fault zones and their impact on aquifers. For example, how geologic andhydrologic information can be best integrated to effectively constrain regional-scale faultpermeability? While existing knowledge on fault permeability at small scales is indispensablescientifically, ultimately, it is the regional-scale permeability that is needed in conceptual andnumerical models for solving problems related to water resource management and transport offluid, solute, and energy in the Earth's crust.The scientific objective of this research is to characterize fault-zone permeability at the wellfieldto regional scale with constraints from field-based structural observations, hydrogeologictesting, and interpretation from conceptual and numerical modeling. The basis hypotheses arethat distinctive hydrogeologic responses around a fault could be observed from cross-faultaquifer tests and that fault-zone permeability features could be established from a comprehensiveunderstanding of the outcrop structural characteristics, borehole data of host rocks, andhydrogeologic tests conducted at multiple scales. Using the Elkhorn thrust fault in Colorado as afield site, the research plan consists of the following: (1) to characterize the geology and internalstructure of the fault zone to better understand the influence of juxtaposition of differentlithologies on fault-zone hydrogeologic properties, (2) to drill and core new boreholes throughthe fault zone to obtain direct field observations for fault-zone permeability, (3) to conduct crossfaultpumping tests in the new and preexisting holes to provide the much need directmeasurements on fault-zone permeability, and (4) to develop a fault-zone permeability model,through numerical modeling that integrates geologic, hydrogeologic, and geophysical field data.Three aspects of the intellectual merit are recognized. First, the study takes a new directionin characterizing fault-zone permeability by closely linking geologic observations andhydrogeologic testing data. Second, this proposed research offers the opportunity to gainhydrogeologic insight into a particular type of fault that is common but highly understudied - a thrust fault with a crystalline hanging wall and sedimentary footwall at regional basin scales. Finally, the cross-fault permeability tests coupled with geologic characterization planned in this research will be a significant advance in characterizing fault-related permeability by providing much-needed field measurement data.The major aspect of the broader impact of this proposed research is on enhancingundergraduate students experience in hydrogeology, in addition to training graduate students and contributing to better groundwater resource management in the western US. This research will benefit a large group of undergraduate students. Undergraduate students will be involved in all stages of this project. Specific approaches to implement this commitment include: (1) Recruit top undergraduates to conduct honor theses, (2) Field exercise related to an upper-division hydrogeology class. Groundwater level mapping and aquifer tests can be incorporated into class related activities, and (3) Drilling new boreholes will be coordinated so that students can observethe operation. Finally, the PIs plan to co-teach a two-credit two-week summer undergraduate field hydrogeology class. The research will provide an excellent venue for many different projects for this field class and help to realization of this plan.