Assessing the roles of wear and roughness on dynamic fault friction

孕育地震的断层自然是粗糙的。断层表面上粗糙的小块可能会碰撞并锁定，阻止断层上的任何进一步运动。地震开始时，这些粗糙的补丁打破，地震的特点是由摩擦过程控制的断层表面演变为地震发生。这个项目将通过探索两种可能在地震期间调节断层摩擦的机制来促进我们对地震物理学的理解。第一种情况发生在加热导致流体压力增加时，这可以通过润滑促进地震中的持续滑动，第二种情况是由于为润滑流体产生更多空间而硬化，这可以阻止地震。为了更好地理解这些过程，PI将在类似地震的条件下使用布朗大学的一种变形装置进行实验。PI将测试自然故障粗糙度和磨损过程对两个竞争过程的作用。这项工作的结果将促进我们对地震物理学的理解，并将为新的和现有的地震破裂模型的开发和修改提供信息。这些模型通过提高对地震过程的理解，在减轻全球地震灾害和风险方面发挥着至关重要的作用。该项目还将使PI继续参与DEEPS核心，这是一个为当地普罗维登斯公立学校开发和实施STEM课程的计划。DEEPS CORES旨在扩大代表性不足的群体在STEM领域的参与，并提高公众的科学素养。基于物理的本构方程描述地震滑动过程中地质材料的摩擦行为的实验验证是推进基于物理的地震动态破裂模型的关键一步。这项工作将使用新修改的Tullis旋转剪切仪在布朗大学进行几套动态岩石摩擦实验，调查两种机制，可能会在地震中调节断层的摩擦行为：热孔隙流体加压弱化（TPW）和粘性硬化（DH）。TPW是由于孔隙流体热膨胀速度快于断层孔隙而产生的。在地震滑动期间排水不良的条件下，这导致孔隙压力增加，从而降低作用于断层的剪切应力，从而削弱断层。DH具有相反的效果，其中剪切导致新的微裂纹的形成，增加总孔隙体积，从而降低孔隙流体压力并加强断层。只有当DH最小时，TPW才在地震期间显著。为了阐明磨损和断层粗糙度对动态摩擦的作用，并探索TPW和DH之间的平衡，PI正在进行滑动速率高达1 m/s、高围压（45 - 60 MPa）和高孔隙压力（25 - 40 MPa）的实验，这些实验在具有可变渗透率和滑动表面粗糙度的样品上进行，模拟在自然界断层上测量的断层粗糙度范围。力学数据将与微观结构分析和微观力学建模相结合，以指导结果的分析和解释。这些实验将是第一个独立控制和升高的孔隙压力，围压，和正常的应力在1米/秒的滑动速率。它将建立条件，在这种条件下，自然断层粗糙度增强了磨损过程，允许TPW在具有不同渗透率的样品中发展，还将建立DH在高位移时抵消粗糙表面上TPW的程度。地球物理学计划和促进竞争性研究的既定计划（EPSCoR）该奖项反映了NSF的法定使命，并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，被认为值得支持。

Faults that host earthquakes are naturally rough. Rough patches on fault surfaces can collide and lock, preventing any further movement on a fault. Earthquakes begin when these rough patches break, and earthquake characteristics are controlled by frictional processes at the fault surface that evolve as the earthquake occurs. This project will advance our understanding of the physics of earthquakes by exploring two mechanisms that may regulate the friction of faults during earthquakes. The first occurs when heating leads to increased pressure in fluids, which can promote continued slip in earthquakes through lubrication, and the second is hardening due to producing more space for the lubricating fluids, which can impede earthquakes. To better understand these processes, the PI will conduct experiments at earthquake like conditions using a one-of-a-kind deformation apparatus at Brown University. The PI will test the roles of natural fault roughness and wear processes on the two competing processes. The results from this work will advance our understanding of earthquake physics and will inform the development and modification of new and existing earthquake rupture models. These models play a vital role in mitigating earthquake hazard and risk worldwide by improving the understanding of earthquake processes. This project will also enable the PI’s continued participation in DEEPS CORES, a program that develops and implements STEM curriculum for local Providence public schools. DEEPS CORES aims to expand participation in STEM fields from under-represented groups and to improve science literacy of the general public.Experimental validation of physics-based constitutive equations that describe the frictional behavior of geologic materials during seismic slip is a critical step in advancing physics-based dynamic rupture models for earthquakes. This work will use the newly modified Tullis Rotary Shear Apparatus at Brown University to conduct several suites of dynamic rock friction experiments investigating two mechanisms that may regulate the frictional behavior of faults during earthquakes: thermal pore-fluid pressurization weakening (TPW) and dilatancy hardening (DH). TPW occurs as frictionally heated pore fluids thermally expand faster than the fault pores. In poorly drained conditions during seismic slip, this leads to increases in the pore pressure that decrease the shear stress acting on the fault thereby weakening the fault. DH has the opposite effect in which shearing causes the formation of new microcracks increases total pore volume, thereby reducing pore fluid pressure and strengthening faults. TPW will only be significant during earthquakes if DH is minimal. To elucidate to roles of wear and fault roughness on dynamic friction and explore the balance between TPW and DH, the PI is conducting experiments at slip rates up to 1 m/s, elevated confining pressures (45-60 MPa), and elevated pore pressures (25-40 MPa) on samples with both variable permeability and sliding surface roughness mimicking the range of fault roughness measured on faults in nature. Mechanical data will be combined with microstructural analysis and micromechanical modelling to guide the analysis and interpretation of results. These experiments will be the first with independently controlled and elevated pore pressure, confining pressure, and normal stress at slip rates of 1 m/s. It will establish conditions under which wear processes, enhanced by natural fault roughness, allow TPW to develop in samples with varying permeabilities and will also establish the extent to which DH counteracts TPW on rough surfaces at high displacements.This project is jointly funded by the Division of Earth Sciences, Geophysics Program and the Established Program to Stimulate Competitive Research (EPSCoR).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.