Collaborative Research: Experiments and Simulations at the Nexus of Geophysics, Chemistry, Materials Science and Mechanics to Determine the Physical Basis for Rate-State Friction

合作研究：结合地球物理学、化学、材料科学和力学来确定速率状态摩擦的物理基础的实验和模拟

• 批准号: 1951467
• 负责人: James Batteas
• 金额: $ 16.8万
• 依托单位: Texas A&M University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-01 至 2024-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1951467&HistoricalAwards=false
• 关键词: Collaborative; Research; Experiments; Simulations; Nexus

This project aims to identify the physical processes underlying rock friction. It has strong implications for our understanding of earthquakes and associated hazards. Earthquakes occur periodically; their recurrence is due to the "stick-slip" behavior of large fractures in the Earth’s crust, called faults. A fault "sticks" in the time periods between earthquakes and "slips" during earthquakes. The stick-slip motion arises from the interaction of the elastic (spring-like) behavior of relatively cold rocks and the frictional behavior of faults. Rock friction has been extensively studied in the laboratory because of its relevance to earthquakes. Empirical equations – that is, derived from experimental data rather than based on known mechanisms – describe how friction varies with time and sliding velocity. Computer models use these equations to reproduce a wide range of earthquake-related phenomena. However, the physical and/or chemical processes underlying these equations are still largely unknown; identifying and quantifying them is critical for applying laboratory results to geological faults. Here, the research team investigates these processes at the microscale and nanoscale of the asperities (bumps) on the fault surface where fault rocks are in actual contact. They use atomic force microscopy and nanoindentation to mimic the behavior of single asperities and to measure their behavior at small scales. Feeding the results of experiments into computer simulations that incorporate larger scales, they model and predict the frictional behaviors of rock surfaces. Ultimately, the researchers aim to develop new equations that better capture the behavior of earthquake faults and improve hazard assessment. This project also provides support to two graduate students and a postdoctoral associate. It fosters training for undergraduate students and outreach to high-school students and teachers, notably from underrepresented groups in science.Empirical rate-and-state friction laws, which describe the frictional sliding behavior of faults, are commonly used in earthquake models. Their physical basis is largely unknown, particularly for the equations that describe the evolution of the "state" of a frictional interface. This renders the extrapolation of laboratory results to geological faults fraught with uncertainty. A common explanation of frictional "state" is that it represents the true area of contact on a fault surface; this area evolves (increases) with time or slip due to asperity yielding and creep. An emerging alternative is that contacts strengthen due to chemical bonding at contact junctions. The team previously demonstrated – using single-asperity atomic force microscopy and coordinated with computer simulations, and with nanoindentation experiments - that both mechanisms may contribute to the increase of friction with time (or slip), an effect termed frictional aging. A unifying hypothesis is that asperity creep and chemical bonding occur simultaneously at asperity contacts, but that aging is due primarily to chemical bonding. In this scenario, contact area and chemical bonding are inextricably linked, with asperity yielding and creep providing the contact area upon which chemical bonding occurs. Here, the research team will conduct novel experiments and simulations at the nexus of geophysics, chemistry, materials science, and mechanics to unveil the physical basis for rate-and-state friction. Specifically, they seek to 1) elucidate the roles of yielding and creep of asperities in friction, 2) explore the influences of temperature and fluid chemistry on surface aging and 3) elucidate the roles of slip versus time in state evolution. They employ specimens made of silica and quartz and, for the first time, amorphous alumina, sapphire and feldspar. Results from single-asperity experiments are integrated into simulations which describe the behavior of rough rock surfaces in contact via multiscale modeling. The models incorporate asperity yielding and creep with chemical bonding effects for the first time, allowing new insights into rate-and-state friction behavior of rock surfaces and faults. This project may lead to a paradigm shift with transformative implications for understanding earthquake nucleation, and for the assessment of earthquake hazards and associated risks.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.

该项目旨在确定岩石摩擦的物理过程。它对我们对地震和相关危害的理解具有很大的影响。地震定期发生；它们的复发归因于地壳中大裂缝的“踩粘性”行为，称为断层。在地震期间地震和“滑动”之间的时期中，故障“棍子”。棍子滑移运动来自相对冷岩石的弹性（春季）行为的相互作用和断层的摩擦行为。由于与地震相关，因此在实验室中进行了广泛研究。经验方程（即源自实验数据而不是基于已知机制）的经验方程描述摩擦如何随时间和滑动速度而变化。计算机模型使用这些方程来重现广泛的地震相关现象。但是，这些方程式下的物理和/或化学过程仍然很大程度上是未知的。识别和量化它们对于将实验室结果应用于地质断层至关重要。在这里，研究小组在微观尺度和纳米级调查了这些过程，该过程是断层岩石实际接触的断层表面上的浅层（凸起）。他们使用原子力显微镜和纳米识别来模仿单个不明智的行为，并在小尺度上测量其行为。将实验的结果馈入结合较大尺度的计算机模拟中，它们对岩石表面的摩擦行为进行建模和预测。最终，研究人员旨在开发新的方程式，以更好地捕捉地震断层的行为并改善危害评估。该项目还为两名研究生和一名博士后助理提供了支持。它促进了对本科生的培训，并向高中生和老师进行宣传，尤其是来自科学中代表性不足的群体。经验率和状态摩擦法律描述了故障的摩擦滑动行为，在地震模型中通常使用。它们的物理基础在很大程度上是未知的，特别是对于描述摩擦界面“状态”演变的方程式。这使实验室结果的外推到充满不确定性的地质断层。摩擦“状态”的一个常见解释是它代表了断层表面上的真实接触区域。该区域随着时间或滑移而演变（增加），因为屈服和蠕变。一个新兴的替代方法是，由于接触连接处的化学键合成而导致的接触可以加强。该团队先前证明了 - 使用单份原子力显微镜并与计算机模拟协调，并通过纳米识别实验进行了协调 - 这两种机制都可能有助于随时间（或滑动）的摩擦增加，这种作用称为摩擦衰老。一个统一的假设是，在阿斯伯特接触处同时发生了阿植度蠕变和化学键合，但衰老主要归因于化学键合。在这种情况下，接触面积和化学键合密不可分，呈阳离子的屈服和蠕变，提供了发生化学键合的接触区域。在这里，研究团队将在地球物理，化学，材料科学和力学的联系中进行新颖的实验和模拟，以揭示速率和状态摩擦的物理基础。具体而言，他们寻求1）阐明摩擦中悬垂性的屈服和蠕变的作用，2）探索温度和流体化学对表面衰老的影响，以及3）阐明了滑移时间与状态进化中的作用。他们采用由二氧化硅和石英制成的物种，并首次使用无定形氧化铝，蓝宝石和长石。单份实验的结果集成到模拟中，这些模拟描述了通过多尺度建模在接触中的粗糙岩石表面的行为。这些模型首次结合了具有化学键合效应的屈服和蠕变，从而使对岩石表面和断层的速率摩擦行为有了新的见解。该项目可能导致范式转变，对了解地震核的变革性影响，并评估地震危害和相关风险。该奖项反映了NSF的法定任务，并通过使用基金会的智力优点和更广泛的影响来诚实地认为，通过评估诚实地支持了审查标准。