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

对暴露于科罗拉多Sawatch山脉的连接的充满假玄武玻璃的发震断层和相关的糜棱岩-超糜棱岩塑性剪切带进行地质观测，以研究中地壳震源深度的地震断层力学。详细的野外和实验室观测的变形构造在所有尺度上集中在三个相关方面的断层在深度：（1）破裂方向性和过程有关的障碍和凹凸体在雁列断层阵列和扇展：（2）机制的断层启动，联动，和应力/应变传递的个别断层系统内;（3）摩擦断裂（假玄武玻璃体系）与同时代塑性蠕变（糜棱岩-超糜棱岩剪切体系）的耦合与分异。该项目将详细的实地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、电子探针和电子背散射衍射方法）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与地震过程之间的联系。项目成果将为中地壳地震过程和塑性不稳定性的模型提供经验性地质限制，并阐明上地壳的瞬时弹性应变如何可能与下地壳的缓慢塑性蠕变和流动相结合，本项目将利用两个大的、绘制良好的假玄武质断层系统来研究地震过程。假玄武玻璃是地震滑动过程中沿沿着断层快速熔融而产生的，可以记录地震事件的详细记录。科罗拉多的萨沃奇山脉经过十多亿年的侵蚀和隆起，已经暴露出了来自中地壳的断层岩，而最大的地震通常是起源于那里。因此，可以观测到远超出直接观测或科学钻探范围的深层地震过程所产生的构造。该项目将提供经验观察，以帮助改进断层如何破裂产生地震的模型。地质结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较浅深度断层的直接观测，从而更全面地了解地震力学。将通过在康科德大学的本科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，促进对下一代地球科学家的培训。该项目的教育影响将通过与康科德的麦克奈尔学者计划密切合作来加强，以促进第一代大学生和代表性不足的群体的科学事业。

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.