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

本计画的目标是：（1）扩大一个初步的微观力学模型，以研究横跨孕震区的颗粒尺度同震破坏，（电子背散射衍射和阴极射线发光）和计算（渐近膨胀均匀化）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）应用这一综合框架来量化损伤和其它断裂带微结构对地震各向异性的影响;（3）确定古走滑断层周围的破坏和相关发震构造的时空模式（缅因州的诺伦贝加断层）从大约10-15 km的深度挖出：（4）建立一个概念模型，将这种模式与在地表观察到的活动断层的破坏结构联系起来;（5）推广开放源代码的损伤分析软件，计算损伤岩石的体弹性刚度和地震特性。该软件将从天然微结构的电子背散射衍射数据文件或可用于敏感性分析的合成（计算机生成）微结构等应用程序中获取输入。走滑断层（如加州的圣安德烈亚斯断层）由于大地震的反复发生而对生命和财产构成重大威胁。在每次地震中，断层破裂段周围的岩石因个别矿物颗粒的破裂而破碎。在许多地震周期中，这些岩石变得如此受损，以至于它们强烈影响岩石的弹性特性，从而影响地震波的速度和首选传播方向。虽然这些所谓的破坏区对地震灾害非常重要，但缺乏关于它们如何形成的可靠力学模型，而且几乎没有关于活动断层带内这种破坏的垂直范围的信息。此外，目前还没有计算框架可用于计算渐进损伤演化如何影响地震波传播。这项工作的建模和实地结果相结合，将使地震活跃地区的特征得到改善，包括概念和波速模型，可用于更好地预测地面震动的方向和强度。该项目开发的开源代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，包括微裂纹方向和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的分析。在地球科学和材料工程中，人们越来越认识到微破裂对宏观行为的重要性，并越来越有能力对其进行定量处理。该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妇女参与STEM，促进发展多元化、具有全球竞争力的STEM劳动力。

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.