CAREER: Multiscale Mechanics of Fluid Infiltrated Fault Zones- An Integrated Research and Education Plan

地震和山体滑坡是地球上代价最高的自然灾害之一，每年造成数百至数千人死亡和数百万至数十亿美元的损失。导致这些事件开始和随后传播的动力不稳定性与地下充满流体的颗粒材料和岩石在极端地球物理条件下的基本物理--摩擦、破裂、加热和压实--有关。像东北和集集地震这样的事件已经确凿地表明，地震危险严重地取决于潜在的断层物理，包括水力特性的空间非均质性和孔隙压力的产生。流体渗透地质材料变形破坏的细观力学模拟和实际条件下非均匀断裂带地震破裂的计算模拟的前沿是本研究的目的。这为这些关键现象的预测性建模和更好地了解地震风险模型的开发提供了一条途径。综合非线性力学、统计物理、数值方法和地震学的观点，提供了广泛的科学和教育机会，对自然灾害政策和准备以及未来劳动力的技术培训产生了影响。该项目的核心是利用一系列协调良好的活动在地球物理学和机械界之间建立桥梁，包括讲习班、会议和社交媒体平台，这些活动将导致思想的交叉授粉，并培养具有强大跨学科培训的新一代科学家和工程师。对本科生和研究生的专业指导，特别是来自代表性不足社区的专业指导，是拟议教育计划的关键组成部分。这一职业项目的目标是制定一项计划，利用跨学科研究和跨学科教育方法推进地震震源物理学的前沿领域。尽管孔隙流体压力变化在震源成核和传播中具有潜在的主导规律，但利用现有的模拟和实验技术尚未完全了解流体渗透断裂带的多尺度力学。这项研究将通过整合材料科学、力学和计算的新理论工具来应对这一关键挑战，并通过开发一个教育平台来培养一批学生和研究人员，他们本质上是在致力于解决连接地球科学和工程的问题。本职业项目的研究内容包括：(1)利用基于剪切变换区理论的基于物理的连续介质粘塑性模型，从理论上研究了流体饱和断层泥在机械振动存在和不存在的情况下的力学响应。该模型解决了断层泥压实、膨胀、孔隙压力变化和剪切加热之间的复杂反馈机制，从而识别和发现了与非平面剪切带的成核和扩展以及粘滑不稳定性有关的断裂带的复杂强度演化历史。(2)将该新的断裂带模型与弹性体相耦合，利用谱边界积分和有限元相结合的新的数值方法来研究复杂环境下的地震破裂传播。理论模型将根据文献中提供的各种实验室测量和地震观测进行验证。该项目的教育部分旨在(1)通过组织跨学科研讨会和会议座谈会，以及利用社交媒体平台传播跨学科研究产品，促进和丰富材料科学家、岩石机械师和地震学家之间的互动，以及(2)通过各种外展活动、课程材料创新和REUS活动，激励学生，特别是少数族裔和女性学生，学习和参与跨学科研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Earthquakes and landslides are among the costliest natural hazards on earth with hundreds to thousands of lives and millions to billions of dollars lost every year. The dynamical instabilities responsible for the onset and ensuing propagation of these events are linked to fundamental physics- friction, fracture, heating, and compaction- of fluid filled granular materials and rocks in the subsurface subjected to extreme geophysical conditions. Events like Tohoku and Chi-Chi earthquakes have conclusively shown that seismic hazard critically depends on the underlying fault physics including spatial heterogeneity in hydraulic properties and pore pressure generation. Advancing frontiers in micromechanical modeling of deformation and failure in fluid infiltrated geological materials and computational modeling of earthquake ruptures in heterogeneous fault zones under realistic conditions are the objective of this study. This provides a pathway for predictive modeling of these critical phenomena and development of better-informed seismic hazard models. Blending perspectives from nonlinear mechanics, statistical physics, numerical methods, and seismology provides a wide range of scientific and educational opportunities, with impact on natural hazards policy and preparedness as well as technical training of the future workforce. Central to this project is building bridges between the geophysics and mechanics communities using a set of well-coordinated activities including workshops, conferences, and social media platforms which will lead to cross-pollination of ideas and nurturing a new class of scientists and engineers with strong interdisciplinary training. Professional mentoring of undergraduate and graduate students, especially from under represented communities is a critical component of the proposed educational plan. The objective of this CAREER project is to develop a plan to advance frontiers in earthquake source physics using an interdisciplinary research and an interdisciplinary educational approach. Despite the potentially dominating rule of pore fluid pressure variations in earthquake source nucleation and propagation, the multiscale mechanics of fluid infiltrated fault zones is not yet fully understood using the current modeling and experimental techniques. This study will address this critical challenge by integrating novel theoretical tools from material science, mechanics and computation and by developing an educational platform that nurtures a class of students and researchers who are intrinsically motivated in working on problems bridging geoscience and engineering. The research component of this CAREER project aims (1) to theoretically investigate the mechanical response of fluid saturated gouge layers sheared in the presence and absence of mechanical vibrations using a novel physics-based continuum viscoplasticity model based on Shear Transformation Zone theory. The model resolves complex feedback mechanisms between gouge compaction, dilation, pore pressure changes and shear heating leading to identification and discovery of complex strength evolution histories in fault zones connected with nucleation and propagation of nonplanar shear bands and stick-slip instabilities, and (2) to couple this new fault zone model with the elastic bulk to investigate earthquake rupture propagation in complex settings using a new numerical technique that couples spectral boundary integral and finite element methods. The theoretical models will be validated against a variety of laboratory measurements and seismic observations available in the literature. The educational component of this project aims (1) to facilitate and enrich interactions between material scientists, rock mechanicians and seismologists, through organization of interdisciplinary workshops and conference symposia, as well as leveraging social media platforms for disseminating interdisciplinary research products, and (2) to inspire students, especially minority and female students, to learn and participate in interdisciplinary research through various outreach activities, curricular material innovation, and REUs engagement.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.