MARGINS FELLOWSHIP: Fluidization of Very Thick Granular Layers in Ancient Thrust Faults

孕震断层--即产生重大地震的断层--特别令人感兴趣，因为它们产生的地震可能造成可察觉的破坏和生命损失。因此，非常重要的是要了解它们在脆性状态下失效的机制--即断裂而不是流动。颗粒层是在脆性区域形成的断层的普遍特征，它们的演化和行为已被证明与强度和应变率关系密切。在实验室中，合成样品和天然样品的行为已被证明受到各种因素的影响，如颗粒大小和粒度分布、层厚度和流体饱和度。这些材料的动态弱化的理论机制已经被提出和探索，但还没有在现场进行检验。对断层的现场观察表明，颗粒层以悬浮液的形式流态化或变形，其行为类似于粘性流体。因此，必须研究这些因素在天然断层环境中的作用，并用断层中的原位颗粒层观测来约束这些参数。这项由两名女性研究人员进行的研究将比较两个成熟的大型脆性断层(一个在阿拉斯加，一个在非洲)，它们含有非常厚的流态化颗粒层，这些颗粒层含有断层活动期间显著流动的证据。流态化颗粒层的结构有可能解释断层的滑动速度，以及在地震旋回期间断层总强度的变化。在其更广泛的影响中，这项研究将促进年轻女性研究员克里斯蒂·罗博士的职业发展，包括她重新融入美国学术界。此外，还将与南非和纳米比亚科学家开展重要的国际合作。该项目具有很高的社会相关性，因为它解决了地震风险的原因。

Seismogenic faults - that is, faults that generate earthquakes of significant magnitude, are of particular interest because the earthquakes they produce can cause appreciable damage and loss of life. It is thus very important to understand the mechanisms by which they fail in the brittle regime - i.e., by fracture as opposed to flow. Granular layers are ubiquitous features of faults that form in the brittle regime, and their evolution and behavior have been shown to be critically related to strength and strain rate relationships. In the laboratory, the behavior of both synthetic and natural samples has been shown to be affected by a variety of factors, such as grain size and size distribution, layer thickness, and fluid saturation. Theoretical mechanisms for dynamic weakening of these materials have been proposed and explored, but not examined in the field. Field observations of faults suggest that granular layers fluidize or deform as a suspension that behaves like a viscous fluid. It is therefore essential to examine the role of these factors in natural fault settings and constrain these parameters with observations of in situ granular layers in faults. This study by two female researchers will compare two large, mature brittle faults (one in Alaska, and one in Africa) that contain very thick fluidized granular layers that contain evidence for significant flow during fault activity. The structure of fluidized granular layers has the potential to elucidate the rate at which the fault slipped, as well as the changes in overall strength of faults during the seismic cycle. Among its broader impacts, this study will advance the career development of a young female researcher, Dr. Christie Rowe, including her reintegration into the US academic community. In addition, there will be significant international collaboration with South African and Namibian scientists. The project has high societal relevance in that it addresses the causes of earthquake risk.