Earthquake mechanics on faults that operate at low average levels of prestress

越来越多的观测证据表明，倾向于产生大的破坏性地震的主要成熟断层是“弱的”，即产生地震的平均应力水平远低于基于0.6至0.8的典型静摩擦系数和覆盖层减去静水孔隙压力的断层正应力的预期。 已经提出了两类模型来解释这种低应力行为：（I）慢性弱断层，无论是在缓慢（准静态）和快速（地震）滑动，和（II）准静态强，但同震弱断层，静态电阻是高的平均值，但大大减弱地震滑动率。 在这个项目中，研究人员建议建立两类低应力断层的断层模型，模拟长期的滑动历史，包括地震序列的断层，并探讨两类模型之间的地震和抗震性能的相似性和差异，以及模型和天然断层之间。该项目的目的是确定一套模型，可以再现一系列强大的观测成熟的故障在各种设置。作为研究的一部分，他们计划调查地震成核在整体断层行为中的作用，探索地震和长期行为之间的关系，并测试简化的准动态地震模拟方法捕获完全动态模型结果的能力。 该项目将导致更好地了解成熟断层上的潜在地震情景，包括成核和非均匀性的作用。 这种理解将有助于开发早期预警算法，并制定用于地震工程的地震情景套件。 结合波传播和场地及建筑物反应的规范，模拟地震序列的方法可以成为人口密集地区地震危险性分析的物理模拟能力的重要组成部分。

Accumulating observational evidence suggests that major mature faults, which tend to produce large, destructive earthquakes, are "weak", i.e. produce earthquakes at average stress levels much lower than expected based on typical static friction coefficients of 0.6 to 0.8 and fault-normal stresses of the order of overburden minus hydrostatic pore pressure. Two classes of models have been proposed to explain such low-stress behavior: (I) chronically weak faults, both during slow (quasi-static) and fast (seismic) slip, and (II) quasi-statically strong but co-seismically weak faults, for which static resistance is high on average, but weakens substantially at seismic slip rates. In this project, the investigator proposes to build fault models representative of the two classes of low-stressed faults, simulate long-term slip histories on such faults that include sequences of earthquakes, and explore similarities and differences in both seismic and aseismic behavior between the two classes of models, and between the models and natural faults. The project aims to determine the set of models that can reproduce a range of robust observations about mature faults in various settings. As a part of the study, they plan to investigate the role of earthquake nucleation in overall fault behavior, explore the relation between seismic and long-term behavior, and test the ability of simplified, quasi-dynamic, methods of earthquake simulation to capture the results of the fully dynamic models. The project will lead to better understanding of potential earthquake scenarios on mature faults, including the role of nucleation and heterogeneity. Such understanding would contribute to developing algorithms for early warning and formulating suites of scenario earthquakes for use in earthquake engineering. Combined with codes for wave propagation and site and building response, the methodology for simulating earthquake sequences can become a vital ingredient of physics-based simulation capability for seismic hazard analysis in densely populated areas.