Collaborative Research: Earthquake Dynamics and Frictional-Plastic Coupling at Hypocentral Depths: Insights From Pseudotachylyte Systems

对科罗拉多州萨瓦奇山脉出露的相互关联的假玄武岩充填的发震断裂和相关的糜棱岩-超糜棱岩塑性剪切带进行了地质观测，以研究地壳中部震源深处的地震断裂机制。对各种尺度的形变结构的详细野外和实验室观测集中于深部断裂的三个相关方面：(1)断裂方向性和与梯形断层阵列和扇形展布中的障碍物和凹凸体有关的过程；(2)断裂的启动、连接和系统内单个断裂之间的应力/应变传递机制；(3)摩擦断裂作用(假硅质岩系统)和同时代塑性蠕变(糜棱岩-超糜棱岩剪切系统)之间的耦合和分配。该项目将详细的野外研究与实验室分析和成像(光学显微镜以及扫描电子显微镜、电子探针和电子背向散射衍射法)相结合，以开发断层/剪切带运动学和动力学模型，并阐明微观变形机制和地震过程之间的联系。该项目的成果将为中地壳地震过程和塑性不稳定模型提供经验地质约束，并阐明上地壳的瞬时弹性应变如何与下地壳的缓慢塑性蠕变和流动相耦合。本项目将通过利用两个映射良好的大型假玄武岩断层系统来研究地震过程。假玄武岩是在地震滑动过程中沿断层闪速熔融而产生的，可以详细记录地震事件。科罗拉多州萨瓦奇山脉10亿多年的侵蚀和隆起暴露了中地壳的断层岩，那里通常是最大的地震的发源地。因此，可以观测到由深部地震过程产生的远远超出直接观测或科学钻探范围的构造。该项目将提供经验观察，以帮助改进断层破裂如何产生地震的模型。地质成果将补充地震波的地球物理观测、地震过程的地球动力学计算机模型，以及对浅层断层的直接观测，以提供更完整的地震力学图景。下一代地球科学家的培训将通过在康科德大学的本科生野外地质学课程和蒙大拿州立大学的研究密集型研究生课程之间建立联系来促进。该项目的教育影响将通过与康科德麦克奈尔学者计划的密切合作来加强，以促进第一代大学生和代表性不足群体的科学事业。

Geologic observations of linked pseudotachylyte-filled seismogenic faults and related mylonite-ultramylonite plastic shear zones exposed in the Sawatch Range, Colorado, to investigate the mechanics of seismic faulting at mid-crustal hypocentral depths. Detailed field and laboratory observations of deformation structures at all scales focus on three related aspects of faulting at depth: (1) rupture directivity and processes related to barriers and asperities in en echelon fault arrays and fanning splays; (2) mechanisms of fault initiation, linkage, and stress/strain transfer between individual faults within the system; and (3) coupling and partitioning between frictional faulting (pseudotachylyte system) and coeval plastic creep (mylonite-ultramylonite shear system). The project combines detailed field studies with laboratory analysis and imaging (optical microscopy as well as scanning electron microscope, electron microprobe, and electron backscatter diffraction methods) to develop a model of fault/shear zone kinematics and dynamics and to elucidate the linkage between microscopic deformation mechanisms and seismic processes. Project results will provide empirical geologic constraints for models of mid-crustal earthquake processes and plastic instabilities and shed light on how transient elastic strain in the upper crust may be coupled to slow plastic creep and flow in the lower crust.This project will investigate earthquake processes by exploiting two large and well-mapped pseudotachylyte fault systems. Pseudotachylytes are produced by flash melting along faults during seismic slip and can record a detailed record of seismic events. More than a billion years of erosion and uplift in the Sawatch Range of Colorado has exposed fault rocks from the middle crust where the largest earthquakes typically originate. Thus, structures produced by deep seismic processes that are far beyond the range of direct observation or scientific drilling can be observed. The project will contribute empirical observations to help improve models of how faults rupture to produce earthquakes. The geologic results will complement geophysical observations of seismic waves, geodynamic computer models of earthquake processes, and direct observations of faults at shallower depths to give a more complete picture of earthquake mechanics. Training of the next generation of earth scientists will be promoted by building a connection between the undergraduate field geology program at Concord University and the research-intensive graduate program at Montana State University. The educational impact of the project will be enhanced through close cooperation with the McNair scholars program at Concord to promote science careers for first generation college students and under-represented groups.