CAREER: Faults, fluids, friction, and fracture mechanics

是什么决定了断层的摩擦强度以及断层滑动在空间和时间上的分布情况？长期以来，人们的焦点一直是地震产生的动态破裂导致的滑动和应力释放的快速积累，地震间隔期被视为相对平静的时期；然而，最近对缓慢、无地震滑动的观察和迹象提出了关于断层在整个地震周期中运行的基本问题。跨主要断层的相对运动在这种缓慢滑动中占多大比例；它如何适应沿断层的应力释放和传递；是什么允许这种稳定但加速的滑动速度及其迁移；从观察到的强迫或断层或整体流变性可以推断出什么？在最近的工作中，研究人员提出了对缓慢断层滑动可能如何启动和传播作为不同强迫条件的响应的定量理解。我们发现，在主要驱动因素的响应下，存在缓慢、稳定的断层滑动的解析解，这些主要驱动因素包括断层上的突然应力台阶、自由容纳较高断层滑动速率的区域和流体来源。这种新的分析方法提供了几种基于远程和本地观测来识别故障运行的方法。这些数据包括监测流体注入和无地震断层位移的最新现场钻孔实验数据，以及关于慢滑移和力矩释放速率的大地测量和地震学推断。这样的观测将直接与上述类型的解进行比较，以确定断层摩擦、弹性和强迫条件的耦合是否足以解释所观察到的行为；如果是，则推断摩擦参数、滑动的时空演变和驱动因素的一阶特征。分析解决方案的进一步发展和与实地观察的比较将受益于与MINES、巴黎理工大学和索菲亚·安提波利斯大学教员的国际合作。针对一个常见的问题，即识别机制相互作用产生的简单但基本的标度，PI将开发一系列实验演示，以激发初中生对STEM的兴趣。开发将与塔夫茨大学的本科生合作完成，塔夫茨大学的本科生将通过课堂实验吸引初中生和高中生参与。这些实验将作为定量观察现象的示范和练习，允许与理论模型进行比较。这些演示随后将被改编成本科课程。

What determines the frictional strength of a fault and how is fault slip distributed in space and time? The focus has long been on the rapid accumulation of slip and stress release from earthquake-generating dynamic ruptures with the interseismic period being seen as one of relative quiescence; however, recent observations of and indications for slow, aseismic slip has raised fundamental questions on the operation of faults throughout the seismic cycle. What proportion of relative motion across major faults occurs as such slow slip; how does it accommodate the release and transfer of stress along a fault; what permits this stable, yet accelerated, rate of slip and its migration; and what may be inferred about the forcing or about the fault or bulk rheology from observations?In recent work, the researcher has advanced a quantitative understanding of how slow fault slip may be initiated and propagated as a response to different forcing conditions. We find the existence of analytical solutions for slow, stable fault slip in response to principal driving factors such as sudden steps of stress on a fault, regions freely accommodating elevated rates of fault slip, and fluid sources. The novel analytical approach provides several avenues to identify fault operation on the basis of remote and local observations. These include data from recent field borehole experiments monitoring fluid injection and aseismic fault displacement, as well as geodetic and seismological inference of slow slip migration and moment release rates. Such observations will be directly compared with solutions of the type described above to determine whether the coupling of fault friction, elasticity, and a forcing condition is sufficient to account for observed behavior; and, if so, the inference of frictional parameters, spatiotemporal evolution of slip, and first-order characteristics of the driving factors. Further development of the analytical solutions and comparison with field observations will benefit from international collaborations with faculty at MINES ParisTech and Université Nice Sophia Antipolis. Appealing to a common problem of identifying simple, yet fundamental, scalings arising from the interplay of mechanisms, the PI will develop a series of experimental demonstrations to excite STEM interest in middle and high school students. The development will be done in collaboration with undergraduate students at Tufts University, who will in turn engage middle and high school students through in-class experiments. The experiments will serve as both demonstrations and exercises in quantitative observation of phenomena, permitting comparisons with theoretical models. The demonstrations will subsequently be adapted for undergraduate courses.