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危险的物理过程。 （春季）相对冷岩的行为和岩石的摩擦行为。但是，与地震相关的现象。岩石的实际接触是模仿单个覆盖率的行为，并在小尺度上测量其行为。评估。这是对Aiterface的演变是由于接触连接处的化学粘合而导致的触点。一种摩擦衰老的作用。具体而言，他们寻求1）阐明摩擦中的屈服和蠕变的作用，2）探索温度对表面衰老的影响，3）阐明了由二氧化硅和石英制成的滑移时间的作用。而且，第一次，无定形的氧化铝，蓝宝石和长石。和相关风险。该奖项反映了NSF的任务，并使用基金会的知识分子优点和更广泛的影响审查标准提出了值得评估的评估。