Collaborative Research: Statistical Physics of Fault Behavior - Dynamic Friction, Strain Localization, Comminution, Heat Transfer, and Compaction

地震、山体滑坡、火山和其他自然灾害是代价高昂的公共提醒，提醒人们，隐藏在风景和海岸线美丽背后的地球物理过程也能够通过突然释放储存的能量而造成大规模破坏。导致这些事件开始和随后传播的动力不稳定性与基本物理有关--摩擦、断裂、加热和压实--颗粒材料受到地震断层、山坡和火山中存在的极端地球物理条件的影响。该项目旨在开发颗粒材料在应力作用下的定量预测模型。以物理学为基础的方法使该项目能够以一种基于以前的现象学方法无法达到的方式跨越尺度。虽然颗粒材料在自然界和技术上无处不在，但这些系统的基本物理学还没有得到很好的理解。在地球物理变量和实验室观测数据的推动下，对这些材料进行精确的物理描述，将有助于开发对地震和山体滑坡等自然现象以及食品、制药和建筑行业中出现的颗粒流、运输、堵塞和包装等工艺过程的预测模型。对这些系统中的摩擦、变形和故障的不完全了解限制了制造技术的进步以及对自然灾害的预测。综合力学、统计物理学、土木工程和地球物理学的观点，提供了广泛的科学和教育机会，对自然灾害政策和备灾以及劳动力的技术培训产生了影响。该项目的核心是在赞助机构开发平行管道，目的是扩大和支持代表不足的群体参与STEM领域。活动包括K-12外展，与当地社区大学(香槟的圣巴巴拉城市学院和帕克兰学院)的合作，以及对本科生和研究生的科学、教育和专业指导。本项目建立了一个基于非平衡统计热力学的定量预测理论框架，用于模拟颗粒破碎、温度变化和颗粒形状对横跨广泛速度和正应力范围的剪切泥层摩擦响应的影响。通过对岩石力学和地球物理界获得的砂岩和断层泥实验数据的定量拟合，验证了理论框架的有效性。目标研究包括但不限于：实验室和断层尺度上的应变局部化模式(Riedel、边界、Y带)以及这些不同模式之间的滑动划分；颗粒破碎的动力学及其在断层弱化和断裂带组构演化中的作用；颗粒尺度上材料的热变化特性和闪光过程对瞬时和稳态摩擦响应的影响；颗粒棱角度对剪切泥层体积变化和流变性的影响。该项目将定量的物理参数与涉及孔隙度、温度、孔隙流体压力和摩擦力的现象学速率和状态定律联系起来。将确定宏观动态过程的微观机制，包括粘滑和动态触发。

Earthquakes, landslides, volcanoes, and other natural disasters are costly public reminders that geophysical processes underlying the beauty of landscapes and coastlines are also capable of massive destruction through the sudden release of stored energy. The dynamical instabilities responsible for the onset and ensuing propagation of these events are linked to fundamental physics?friction, fracture, heating, and compaction-- of granular materials subject to extreme geophysical conditions present in earthquake faults, hillsides, and volcanoes. This project aims to develop quantitative, predictive models of granular materials under stress. The physics-based approach enables the project to span scales in a manner that is inaccessible based on previous phenomenological methods. While granular materials are ubiquitous, in both nature and technology, the fundamental physics of these systems is not well understood. Development of a precise, physical description for these materials, motivated by geophysical variables and laboratory observables, will contribute to development of predictive models for natural phenomena, such as earthquakes and landslides, as well as technological processes, including granular flow, transportation, jamming, and packing, that arise in food, pharmaceutical, and construction industries. The incomplete understanding of friction, deformation, and failure in these systems limits progress in manufacturing technologies as well as forecasting natural hazards. Integrating perspectives from mechanics, statistical physics, civil engineering, and geophysics provides a wide range of scientific and educational opportunities, with impact on natural hazards policy and preparedness as well as technical training of the workforce. Central to the project is development of parallel pipelines at the sponsored institutions, aimed at broadening and supporting participation of underrepresented groups in STEM fields. Activities include K-12 outreach, collaboration with local community colleges (Santa Barbara City College and Parkland College in Champaign), and scientific, educational, and professional mentoring of undergraduate and graduate students. This project establishes a quantitative, predictive theoretical framework, based on non-equilibrium statistical thermodynamics, for modeling the influence of grain breakage, temperature variations, and grain shape on the frictional response of sheared gouge layers spanning a wide range of velocities and normal stresses. The theoretical framework is validated by quantitative fits to experimental data on sand and fault gouge obtained in the rock mechanics and geophysics communities. Target investigations include, but are not limited to the following: strain localization patterns (Riedel, boundary, Y-band) at laboratory and fault scales and partitioning of slip between these different modes; dynamics of grain breakage and its role in fault weakening and the evolution of fault zone fabric; effects of thermally-varying material properties and flash processes at the grain scale on transient and steady state frictional response; effect of grain angularity on volume changes and rheology of sheared gouge layers. The project links quantitative physical parameters to phenomenological rate-and-state laws involving porosity, temperature, pore fluid pressure, and friction. Microscopic mechanisms underlying macroscopic dynamic processes, including stick slip, and dynamic triggering will be identified.