Integration of the Physical and Chemical Rock Properties, Structure, and Permeability of the San Andreas Fault, San Andreas Fault Observatory at Depth Borehole, California

10年前，作为地球镜的圣安德烈亚斯断层观测站深度钻孔的一部分，从大约3公里深的圣安德烈亚斯断层的一个活跃蠕动痕迹上收集了大约40米的整个岩芯。SAFOD岩心的每一厘米取样都是极其宝贵的，代表了对活跃板块边界断层的罕见看法。整个项目的目的是通过检查整个岩芯样本和综合各种地质和地球化学数据，为发生在圣安德烈亚斯断层沿着以及更广泛地说世界各地活动断层内的地震提供更现实的限制。地震发生时，断层移动岩石，以回应地壳内的应力。在地震之前、期间和之后，岩石记录了与这个周期相关的物理和化学变化。地震和相关灾害对社会构成重大风险，可能导致生命损失、严重伤害、基础设施损坏和重大经济影响。这项工作有助于发展更好的约束地震地面震动和地震安全风险模型的活动断层系统。与本科生和研究生合作，该项目将为本科非专业和社区大型活动创建引人入胜的互动学习模块，这些活动有助于SAFOD和Earthscope数据的遗产，并提高学生和公众对地震地质学领域的认识。这项研究的重点是在深度的圣安德烈亚斯断层的结构和组成，使用现有的范围内的岩屑，侧壁岩心，全岩芯，和井下地球物理测井数据从Earthscope的圣安德烈亚斯断层观测深度钻孔。 具体而言，拟议的研究旨在：1）检查变形和滑动局部化的机制，断裂带内流体-岩石相互作用的颗粒-断层尺度性质，并确定断裂带中碳质物质的起源、性质和作用，检验含碳断层岩影响滑动弱化和局部化或作为地震引起的流体迁移的指示的假设。将断层带组成和结构的新结果与基于钻孔的数据结合起来，以确定断层带的弹性特性，检查随时间变化的化学和物理断层带过程的性质和意义，并将材料特性与影响断层带内和附近能量分布的关键弹性参数联系起来。 3)综合和重新评估SAFOD的地质，地球化学和岩石性质的众多研究小组的所有已发表和可访问的结果与我们的新结果，以开发断层带结构和性质的预测示意图模型，然后我们将其与弹性模量相关。4)教育和指导学生成为有竞争力的STEM劳动力成员和有效的科学传播者，通过参与研究和互动教育活动的发展，有助于SAFOD和Earthscope数据的遗产，并提高学生和公众对地震地质和地震灾害的认识。SAFOD岩心提供了一个机会，可以严格检查现场断层岩石样本，以破译影响地震滑动和地震蠕变的过程。显微镜和地球化学的系统集成使我们能够了解动态的，复杂的，非均质断裂带的构造成岩作用。在流体-岩石相互作用期间的大规模蚀变残留，以及变形期间复杂的显微结构变化，如果没有各种尺度的不同技术，则难以解决。使用高分辨率显微镜、地球化学和岩石性质评估的拟议跨学科方法涵盖了广泛的尺度和方法，并将进一步有助于我们破译物理化学过程的能力（例如，压力、温度、渗透率、流体成分和来源）从与断层中微观尺度的流体迁移相关的过程（例如，热加压）。该项目将扩大对断层弱化过程中流体作用的了解，限制地震周期中微观尺度上与流体迁移相关的条件，并确定主要构造断层的强度和滑动行为的演变，以进行地震危险性评估。新的综合数据集将向整个科学界开放，正如最初的Earthscope倡议所设想的那样，并致力于回答Earthscope在2010年确定的一个悬而未决的问题：地震期间的滑动分布是什么，我们可以从断层几何形状和断层流变学的非均质性中学到什么？该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

Ten years ago, about 40 m of whole rock core was collected from a depth of approximately 3 km across an actively creeping trace of the San Andreas Fault as part of Earthscope's San Andreas Fault Observatory at Depth Borehole. Every centimeter of SAFOD core sampled is extremely valuable and represents a rare view into an active plate boundary fault. The aim of the overall project is to provide more realistic constraints for earthquakes that occur along the San Andreas Fault and, more broadly, within active faults around the world through the examination of whole rock core samples and a synthesis of a variety of geological and geochemical data. Earthquakes occur as faults displace rocks in a response to stress within the Earth's crust. Before, during, and after an earthquake, the rocks record physical and chemical changes that are associated with this cycle. Earthquakes and associated hazards pose a significant risk to society that may result in loss of life, serious injuries, damage to infrastructure, and major economic impacts. This work contributes to the development of better constraints for earthquake ground-shaking and seismic safety hazard models for active fault systems. Working with undergraduate and graduate students, the project will create engaging and interactive learning modules for undergraduate non-majors and community-at-large events that contribute to the legacy of SAFOD and Earthscope data, and increase students' and the general public's awareness about the field of Earthquake Geology. This study is focused on the structure and composition of the San Andreas Fault at depth using the available range of cuttings, sidewall cores, whole-rock core, and downhole geophysical logging data from Earthscope's San Andreas Fault Observatory at Depth Borehole. Specifically, the proposed research aims to: 1) Examine the mechanisms of deformation and slip localization, the grain- to fault-scale nature of fluid-rock interactions within the fault zone, and to determine the origin, nature, and roles of carbonaceous matter in the fault zone, testing the hypothesis that carbon-bearing fault rocks influence slip weakening and localization or serve as indicators for earthquake induced fluid migration.2) Couple new results on fault zone composition and structure with borehole-based data to determine the elastic properties of the fault zone, to examine the nature and significance of time-dependent chemical and physical fault zone processes, and to relate the material properties to key elastic parameters that affect the energy distributions in and near fault zones. 3) Synthesize and re-evaluate all published and accessible results by numerous research groups of the geology, geochemistry, and rock properties of SAFOD with our new results, to develop a predictive schematic model of fault zone structure and properties, which we will then relate to its elastic moduli. 4) Educate and mentor students to become competitive STEM Workforce members and effective science communicators through participation in research and in the development of interactive educational activities that contribute to the legacy of SAFOD and Earthscope data, and increasing students' and the general public's awareness of earthquake geology and seismic hazards. The SAFOD core provides an opportunity to rigorously examine in situ fault-rock samples in order to decipher the processes that influence seismic slip and aseismic creep. Systematic integration of microscopy and geochemistry enables us to understand structural diagenesis in dynamic, complex, and heterogeneous fault zones. Remnants of extensive alteration during fluid-rock interactions, and complex microstructural changes during deformation are difficult to resolve without diverse techniques at various scales. The proposed interdisciplinary approach using high-resolution microscopy, geochemistry, and evaluation of rock properties spans a wide range of scales and methods and will further contribute to our ability to decipher the physio-chemical processes (e.g., pressure, temperature, permeability, fluid composition and source) from processes associated with fluid migration at the microscopic scale in faults (e.g., thermal pressurization). The project will expand knowledge of the role of fluids during fault weakening, constrain the conditions associated with fluid migration at the micro-scale during the earthquake cycle, and determine the evolution of strength and slip behavior of major tectonic faults for seismic hazard assessment. The new and synthesized data sets will become accessible to the entire scientific community, as envisioned by the original Earthscope initiative and work towards answering one of Earthscope's outstanding questions identified in 2010: What is the slip distribution during earthquakes and what can we learn from heterogeneities about fault geometry and fault rheology?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.