Dynamic Fragmentation and Earthquake Energy Partitioning

动态破碎与地震能量划分

• 批准号: 2150831
• 负责人: Scott Johnson
• 金额: $ 39.05万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-03-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2150831&HistoricalAwards=false
• 关键词: Dynamic; Fragmentation; Earthquake; Energy; Partitioning

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. Less than 20% of the energy released during an earthquake radiates away from the source as elastic waves that cause ground shaking. A large portion of the energy is dissipated around the fault as frictional heat and through a variety of processes. These processes control how the earthquake rupture propagates. During each earthquake, the rocks surrounding the active fault are fragmented by cracking of individual mineral grains. They form the so-called damage zone. Over many earthquake cycles, damage increases in this zone causing changes in seismic-wave direction and speed. Understanding these processes is critical to evaluate the energy budget through the entire seismogenic zone. It is also critical to assess seismic hazards. Here, the researchers combine field-based results and modeling to improve the understanding of seismically active faults. They quantify processes causing fragmentation in the deeper reaches of the seismogenic zone. They develop wave speed models that can be used to better predict ground shaking directions and intensities. The interdisciplinary project supports a postdoctoral associate, as well as the training of undergraduate and graduate students at University of Maine. The developed codes and analytical protocols are made openly available through public portals. These outcomes can be applied beyond Seismology in Material Sciences and Engineering, notably to investigate brittle fragmentation in ceramics and advanced composite materials. The objectives of this project are: (1) to characterize the microfracture density and fragment size distributions for fragmented minerals in two deeply exhumed seismogenic faults/shear zones; (2) to use the fragment size distributions to estimate the energy that was consumed by fragmentation; (3) to apply physics-based fragmentation modeling to estimate strain rates associated with the fragmentation; (4) to better constrain the energy partitioning in the earthquake source volume; (5) to develop and disseminate protocols for using electron backscatter diffraction techniques to analyze mineral and rock fragmentation. Addressing the above objectives provides an opportunity to test hypotheses related to the source energy budget, styles of rupture propagation, and the relations between loading conditions and resulting rock microstructures in the deeper seismogenic zone. The study also allows evaluating whether intense fragmentation of brittle minerals can be used as a seismogenic signature at depth, as it is at the surface. The chosen approach applies models and concepts that originate largely in the physics and engineering communities, and mostly constitutes novel research in the geosciences. 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. Outcomes of this project will provide a framework for future efforts in both fields, and for collaborations between them.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

由于大地震的反复发生，像加州的圣安德烈亚斯断层这样的走滑断层对生命和财产构成了重大威胁。在地震中，只有不到20%的能量会以弹性波的形式从震源辐射出去，从而引起地面震动。大部分能量以摩擦热的形式在断层周围消散，并通过各种过程消散。这些过程控制着地震破裂的传播。在每次地震中，活动断层周围的岩石因个别矿物颗粒的破裂而破碎。形成了所谓的“破坏区”。在许多地震周期中，该区域的破坏增加，导致地震波方向和速度的变化。了解这些过程对于评估整个孕震区的能量收支是至关重要的。评估地震灾害也至关重要。在这里，研究人员将联合收割机基于现场的结果和建模相结合，以提高对地震活动断层的理解。它们量化了在孕震区较深处造成破碎的过程。他们开发了波速模型，可用于更好地预测地面震动的方向和强度。该跨学科项目支持博士后助理，以及在缅因州大学的本科生和研究生的培训。通过公共门户网站公开提供所制定的守则和分析协议。这些成果可以应用于材料科学和工程中的地震学之外，特别是研究陶瓷和先进复合材料中的脆性破碎。该项目的目标是：（1）确定两个深掘发震断层/剪切带中破碎矿物的微裂缝密度和碎片尺寸分布的特征;（2）利用碎片尺寸分布估计破碎所消耗的能量;（3）应用基于物理的破碎建模来估计与破碎有关的应变率;（4）更好地限制震源体中的能量分配;（5）制定和传播使用电子背散射衍射技术分析矿物和岩石破碎的协议。解决上述目标提供了一个机会，以测试有关的源能量预算，破裂传播的风格，以及加载条件和由此产生的岩石微观结构在更深的孕震区之间的关系的假设。该研究还允许评估脆性矿物的强烈破碎是否可以用作深度的地震信号，因为它是在表面。所选择的方法应用的模型和概念，主要来源于物理和工程界，主要是构成地球科学的新研究。认识到微破裂的宏观行为的重要性和定量处理它的能力正在增长，在地球科学和材料工程。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。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Elastic Contrast, Rupture Directivity, and Damage Asymmetry in an Anisotropic Bimaterial Strike‐Slip Fault at Middle Crustal Depths

• DOI: 10.1029/2021jb023821
• 发表时间: 2022-06
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: B. Song;W. Song;S. E. Johnson;C. Gerbi;S. Vel