Origin and Vertical Extent of Damage Zones Around Continental Strike-slip Faults

该项目的目标是：(1)放大一个跨越孕震带的颗粒尺度同震损伤的初步微观力学模型，该模型集成了分析(电子背散射和阴极发光)和计算(渐近膨胀均一化)方法，并充分考虑了样品中不同矿物之间的颗粒尺度弹性相互作用；(2)应用这个综合框架来量化损伤和其他断裂带微结构对地震各向异性的影响；(3)确定在大约10-15公里深的古走滑断层(缅因州诺鲁贝加断裂)周围出露的损伤和相关的孕震结构的时空格局；(4)开发一个概念模型，将这种模式与地表观测到的活动断裂的损伤结构联系起来；(5)传播用于损伤分析和计算整体弹性刚度和受损岩石地震性质的开源软件。该软件将从自然微结构的电子背向散射衍射数据文件或可用于敏感性分析等应用的人工(计算机生成)微结构中获取输入。加州圣安德烈亚斯断层等行程滑动断层由于大地震的反复发生而对生命和财产构成重大威胁。在每一次地震中，断层破裂段周围的岩石都会因个别矿物颗粒的破裂而破碎。在多次地震循环中，这些岩石会受到严重破坏，严重影响岩石的弹性性质，从而影响地震波的传播速度和首选方向。尽管这些所谓的破坏带对地震灾害非常重要，但缺乏关于它们如何形成的可靠的力学模型，而且几乎没有关于活动断裂带内这种破坏的垂直范围的信息。此外，目前还没有可用于计算渐进损伤演化如何影响地震波传播的计算框架。这项工作的建模和实地结果相结合，将有助于改进地震活动区的特征，包括可用于更好地预测地面震动方向和强度的概念性和波速模型。在这个项目中开发的开放源码将通过现有的公共门户网站提供，并将有许多社区应用程序，包括微裂纹取向和应力状态之间的关系，对地震数据的解释，以及对陶瓷和先进复合材料的脆性破坏和破碎的分析。在地球科学和材料工程学中，人们越来越认识到微压裂对宏观行为的重要性，以及对其进行量化处理的能力。该项目的成果将为这两个领域今后的努力以及它们之间的合作提供一个框架。该项目将通过培训研究生和本科生以及妇女参与STEM，促进发展一支多样化的、具有全球竞争力的STEM劳动力队伍。

The objectives of this project are to: (1) scale-up a preliminary micromechanical model for grain-scale coseismic damage spanning the seismogenic zone that integrates analytical (electron backscatter diffraction and cathodoluminescence) and computational (asymptotic expansion homogenization) approaches and fully account for the grain-scale elastic interactions among the different minerals in the sample; (2) apply this integrated framework to quantify the effects of damage and other fault-zone microstructure on seismic anisotropy; (3) determine the spatial and temporal pattern of damage and related seismogenic structure around an ancient strike-slip fault (the Norumbega fault in Maine) exhumed from a depth of approximately 10-15 km; (4) develop a conceptual model linking this pattern to the damage structure of active faults observed at the surface; and (5) disseminate open-source software for damage analysis and calculation of bulk elastic stiffnesses and seismic properties of damaged rocks. This software will take input either from electron backscatter diffraction data files of natural microstructures, or synthetic (computer generated) microstructures that can be used in sensitivity analyses among other applications.Strike-slip faults like the San Andreas Fault in California represent major threats to life and property owing to the repeated generation of large earthquakes. During each earthquake, the rocks surrounding the ruptured segment of the fault are fragmented by cracking of individual mineral grains. Over many earthquake cycles, these rocks become so damaged that they strongly affect the elastic properties of the rocks, and therefore the speed and preferred propagation direction of seismic waves. Although these so-called damage zones are of great importance for seismic hazards, a robust mechanical model for how they form is lacking, and there is almost no information on the vertical extent of this damage within active fault zones. Furthermore, there is currently no computational framework available for calculating how progressive damage evolution might affect seismic wave propagation. The combination of modeling and field-based results from this work will allow improved characterization of seismically active areas, including conceptual and wave speed models that can be used to better predict ground shaking directions and intensities. The open-source codes developed in this project will be made available through existing public portals, and will have many community applications including the relationships between microcrack orientation and state of stress, interpretation of seismological data, and analysis of brittle damage and fragmentation of ceramics and advanced composite materials. Recognition of the importance of microfracturing for macroscopic behavior and the ability to treat it quantitatively is growing in both Earth sciences and materials engineering. The results of this project will provide a framework for future efforts in both fields, and for collaborations between them. The project will contribute to the development of a diverse, globally competitive STEM workforce through training of graduate and undergraduate students and in participation of women in STEM.