Collaborative Research: Mechanics of Earthquake Fault Zones: Particle Dynamics Simulations and Laboratory Experiments

实验室研究对我们对地震成核、动态破裂和剪切变形的理解做出了重大贡献，然而，这些实验的结果往往难以扩大到自然断层系统。基于粒子的数值模型可以提供帮助，它已经成功地再现了大量观察到的实验室和自然现象。该合作研究项目旨在：(a)改进和完善现有的基于颗粒的数值技术，以更好地复制实验室实验结果，特别是摩擦强度和滑动稳定性的一阶和二阶变化；(2)弥合这些改进模型与自然断层之间的差距，允许研究复杂构造断层的结构演化。在广泛的相同的初始和边界条件下进行。将实验结果与数值结果进行比较，指导数值粒子间接触定律的更新，以更好地再现真实的物理化学表面相互作用。主要的重点是在两组实验中精确地约束滑动摩擦的基础（“拜耳定律”）系数，以及它随剪切、膨胀和压实的变化。重点还将包括摩擦与接触时间和滑移速度的二阶变化，即速率和状态相关的摩擦。数值模型进一步帮助分离不同边界条件下断裂带内的变形机制，包括剪切局部化、晶界滑动、颗粒滚动、平移和断裂。所提出的工作结果将对断层力学和地震物理学的理解产生重大影响，包括断层相互作用、地震触发和地震危险性评估。

Laboratory studies have contributed significantly to our understanding of earthquake nucleation, dynamic rupture, and shear deformation, however, results of these experiments are often difficult to scale up to natural fault systems. Particle-based numerical models, which have successfully reproduced a wide-range of observed laboratory and natural phenomena, can help. This collaborative research project is designed to (a) improve and refine existing particle-based numerical techniques to better replicate laboratory experimental results, in particular, first and second order variations in frictional strength and sliding stability, and (2) bridge the gap between these improved models and natural faults, allowing investigation of the structural evolution of complex tectonic faultsThis research involves parallel laboratory and numerical experiments, conducted under a wide range of identical initial and boundary conditions. The experimental and numerical results are being compared, guiding updates of the numerical interparticle contact laws to better reproduce realistic physico-chemical surface interactions. The primary focus is on accurately constraining the base ("Byerlee's Law") coefficient of sliding friction in the two sets of experiments, as well as its variation with shear, dilation, and compaction. Focus will also include the 2nd-order variations in friction with contact time and slip velocity, i.e., rate- and state-dependent friction. The numerical models further help to isolate the deformation mechanisms acting within the fault zones under different boundary conditions, including shear localization, grain-boundary sliding, particle rolling, translation, and fracture. Results of the proposed work will have significant impact on understanding fault mechanics and earthquake physics including fault interaction, earthquake triggering, and seismic hazard assessment.