Frictional strength evolution and earthquake nucleation

地震是由地质断层破裂引起的。理解这些危险事件需要建立滑动摩擦和断层破裂的数学模型描述。地震预报依赖于这些模型，这些模型受到实验室数据的约束，并假定存在现象学规律。然而，模型预测对所选择的定律高度敏感。PI最近开发了一种新的分析方法来检查这种敏感性。他证明，现有的地震成核和滑动模型可能排除了最小成核大小(或最小地震大小)。在以前的故障模型中，这样的最小尺寸被认为是必需的。在这里，PI和他的团队扩展了这项工作，以统一现有的断层摩擦现象学定律和对动态破裂成核的理解。预期的解决方案可以重新调整地震物理学的理论框架，以适应越来越多的观测证据，这些证据威胁到最小地震规模的范式。因此，该项目对地震建模和预测具有重要意义。它还为一名研究生和一名博士后助理提供支持。这个项目研究了地震断层破裂的成核和传播的基本原理。断层破裂的理论模型通常基于所谓的速率和状态相关的摩擦定律，其中断层强度取决于主岩的滑动速率及其滑动历史或状态。我们对地震成核和滑动摩擦的地震学含义的理解依赖于这些唯象定律。传统上，这些定律被认为意味着最小断层大小是孕育地震所必需的。越来越多的实验摩擦数据导致了摩擦强度演变的几个公式。然而，这些不同的公式产生了不同的地震成核模型预测。PI最近发展了一种新的分析观点，在这种观点中，以前公式中的滑动失稳和地震成核的发生是非线性解的末端。这种方法超越了经典的线性微扰分析，消除了对最小形核尺寸的需要。在这里，PI和他的团队将这项工作扩展到依赖于速率和状态的摩擦定律的一般形式，该定律推进并统一了对所谓的老化和滑移定律的理解。在这项工作中，团队检查了以前和新的关于滑动摩擦的描述，它们在地震过程模型中的作用以及它们的地震学含义。这一奖项反映了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 are generated by the rupture of geologic faults. Understanding these hazardous events requires developing mathematical model descriptions of sliding friction and fault rupture. Earthquake forecasting relies on these models, which are constrained by laboratory data and assume phenomenological laws. However, model predictions are highly sensitive to the chosen laws. The PI recently developed a new analytical approach to examine such sensitivities. He demonstrated that existing models of earthquake nucleation and slip may preclude a minimum nucleation size (or minimum earthquake size). Such a minimum size was thought to be required in prior fault models. Here, the PI and his team extend this work to unify existing phenomenological laws for fault friction and the understanding of dynamic rupture nucleation. The expected solution can realign the theoretical framework of earthquake physics with growing observational evidence that threatens the paradigm of a minimum earthquake size. Consequently, this project has critical implications for earthquake modeling and forecasting. It also provides support for a graduate student and a postdoctoral associate. This project addresses the fundamentals of the nucleation and propagation of an earthquake-generating fault rupture. Theoretical models of fault rupture are often based on so-called rate- and state-dependent friction laws, where fault strength depends on the slip rate of the host rock as well as its sliding history, or state. Our understanding of the seismological implications of earthquake nucleation and sliding friction relies on these phenomenological laws. Traditionally, these laws are thought to imply that a minimum fault size is necessary to nucleate an earthquake. An increasing body of experimental friction data has led to several formulations for frictional strength evolution. However, these different formulations produce disparate model predictions for earthquake nucleation. The PI recently developed a new analytical perspective in which the occurrence of slip instability and earthquake nucleation in previous formulations are end-members of a non-linear solution. This approach moves past the classic linear perturbation analysis and eliminates the need for a minimum nucleation size. Here, the PI and his team extend this work to a generalized form of the rate- and state-dependent friction law that advances and unifies the understanding of the so-called aging and slip laws. In this effort, the team examines previous and new descriptions of sliding friction, their role in models of the earthquake process and their seismological implications.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.