EAR-PF: The interaction between ductile shear zones and the seismogenic crust

Kali L.Allison博士获得了NSF EAR博士后奖学金，在马里兰大学开展研究和教育计划。该研究项目的重点是了解洲际走滑断层(如加利福尼亚州的圣安德烈亚斯断层和新西兰的阿尔卑斯山断层)的结构发展，以及它如何影响在这类断层上发生的地震。像圣安德烈亚斯这样的断层高度局限于地壳浅层，并过渡到地壳深处宽阔的韧性变形带(剪切带)。地震发生在浅层的脆性部分，但它们与韧性剪切带相互作用。这种相互作用的例子包括粘性流动引发的余震，微震活动的时空分布，以及出土断层的微观结构数据。通过模拟大型断裂构造的发展，以及它与地震周期的相互作用，本项目将有助于评估走滑活动断裂所造成的地震危险性。特别是，从脆性变形到韧性变形的转变深度对地震破裂的可能深度施加了限制，因此是对断层上可能发生的最大地震的控制之一。该教育计划将侧重于指导一名本科生使用复杂的计算工具进行研究。艾利森博士还将参加马里兰大学的公共宣传和教育活动。为了研究活动断裂及其韧性根之间的相互作用，PI将开发一个全面的数值模型，在整个地震周期内耦合浅层孕震带和较深的韧性层。该模型将把下地壳中可能重要的微构造过程，如面理作用和颗粒尺寸减小，映射到洲际断层的规模。该项目还将探索继承性结构，如下地壳或上地幔中先前存在的各向异性组构对韧性剪切带发展的影响，以及通过塑性变形自发形成断层的影响。它还将考虑广泛的时间尺度，从地震破裂期间的几分之一秒到洲际断层发展期间的数百万年。因此，该项目将在实验室实验和分析工作的基础上，将我们目前对所考虑的物理机制的理解与大地测量和地质观测联系起来。该模型将产生的可观测结果包括：表面热通量、表面变形的时空模式和剪切带中的平均颗粒尺寸。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Dr. Kali L. Allison has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education plans at the University of Maryland. The research project focuses on understanding the development of the structure of an intercontinental strike-slip fault, such as the San Andreas Fault in California and the Alpine Fault in New Zealand, and how it affects the earthquakes occurring on this type of faults. Faults like the San Andreas are highly localized in the shallow crust, and transition to broad zones of ductile deformation (shear zones) deeper in the crust. Earthquakes occur on the shallow, brittle portion, but they interact with the ductile shear zone. Examples of this interaction include the triggering of aftershocks by viscous flow, the spatio-temporal distribution of microseismicity, and microstructural data from exhumed faults. By simulating the development of the large-scale fault structure, and how it interacts with the earthquake cycle, this project will contribute to assessing the seismic hazard posed by active strike-slip faults. In particular, the depth of the transition from brittle to ductile deformation, which imposes a limit on the possible depth of earthquake rupture, and therefore is one control on the largest earthquake possible on a fault. The education plan will focus on the mentoring of an undergraduate student in research using sophisticated computational tools. Dr. Allison will also participate in public outreach and education activities at the University of Maryland. To investigate the interaction between the active faults and their ductile roots, the PI will develop a comprehensive numerical model that couples the shallow seismogenic zone and deeper ductile layers over the entire seismic cycle. The model will map microstructural processes likely to be significant in the lower crust, such as foliation and grain size reduction, to the scale of intercontinental faults. The project will also explore the effects of an inherited structure, such as a pre-existing anisotropic fabric in the lower crust or upper mantle, on the development of a ductile shear zone, and the spontaneous development of a fault through plastic deformation. It will also consider a broad range of time scales, ranging from fractions of a second during an earthquake rupture to millions of years during the development of an intercontinental fault. Thus, the project will connect our current understanding of the physical mechanisms considered, based on laboratory experiments and analytical work, to geodetic and geologic observations. Observables which will result from the model include: surface heat flux, the spatio-temporal pattern of surface deformation, and the average grain size in the shear zone.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.