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

本项目的目标是：(1)将分析（电子背散射衍射和阴极发光）和计算（渐近膨胀均匀化）相结合的跨震区粒度同震损伤的初步微观力学模型扩大，并充分考虑样品中不同矿物之间的粒度弹性相互作用；(2)应用该综合框架量化损伤和其他断裂带微观结构对地震各向异性的影响；(3)确定从深度约10-15 km的古走滑断层（缅因州Norumbega断层）周围的破坏和相关发震构造的时空格局；(4)建立一个概念模型，将这种模式与在地表观测到的活动断层的破坏结构联系起来；(5)发布损伤分析及损伤岩石体弹性刚度和地震特性计算的开源软件。该软件将从自然微结构的电子后向散射衍射数据文件或可用于灵敏度分析等应用的合成（计算机生成）微结构中获取输入。像加州的圣安德烈亚斯断层这样的走滑断层由于反复发生的大地震对生命和财产构成了重大威胁。在每次地震中，断层破裂部分周围的岩石由于单个矿物颗粒的破裂而破碎。在许多地震周期中，这些岩石受到严重破坏，从而强烈影响了岩石的弹性特性，从而影响了地震波的速度和首选传播方向。尽管这些所谓的破坏带对地震危险非常重要，但缺乏一个可靠的力学模型来解释它们是如何形成的，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，目前还没有可用的计算框架来计算渐进式损伤演化如何影响地震波传播。建模和现场结果的结合将改进地震活跃区的特征，包括可用于更好地预测地面震动方向和强度的概念和波速模型。该项目开发的开源代码将通过现有的公共门户提供，并将有许多社区应用，包括微裂纹方向与应力状态之间的关系，地震数据的解释，以及陶瓷和先进复合材料的脆性损伤和破碎分析。在地球科学和材料工程领域，人们越来越认识到微压裂对宏观行为的重要性，并对其进行定量处理。这个项目的成果将为这两个领域的未来努力以及它们之间的合作提供一个框架。该项目将通过对研究生和本科生的培训以及女性在STEM领域的参与，为培养多元化、具有全球竞争力的STEM劳动力做出贡献。

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.