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

美国科罗拉多州萨沃奇山脉（Sawatch Range）暴露出的相关假长柄岩造震断层和糜棱岩-超糜棱岩塑性剪切带的地质观测，以研究地壳中次中心深度地震断裂的机制。详细的现场和实验室观测在所有尺度上的变形结构集中在三个相关的方面在深度断裂：(1)破裂指向性和过程相关的障碍和凹凸在雁列断层阵列和扇形带状；(2)系统内单个断层之间的断层起始、联动和应力/应变传递机制；(3)摩擦断裂（伪长石体系）与同期塑性蠕变（糜棱岩—超糜棱岩剪切体系）的耦合与划分。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、扫描电子显微镜、电子显微探针和电子背散射衍射方法）相结合，建立了断层/剪切带运动学和动力学模型，并阐明了微观变形机制与地震过程之间的联系。项目结果将为中地壳地震过程和塑性不稳定性模型提供经验地质约束，并阐明上地壳的瞬态弹性应变如何与下地壳的缓慢塑性蠕变和流动相耦合。该项目将通过利用两个大的、绘制良好的伪岩断层系统来研究地震过程。伪岩是地震滑动时沿断层闪融产生的，可以详细记录地震事件。科罗拉多州萨沃奇山脉经过10多亿年的侵蚀和隆起，已经暴露出中地壳的断层岩石，这里通常是最大地震的发源地。因此，可以观察到远远超出直接观测或科学钻探范围的深层地震过程产生的结构。该项目将提供经验观察，以帮助改进断层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，以及浅层断层的直接观测，以提供更完整的地震力学图像。通过在康科德大学的本科实地地质学项目和蒙大拿州立大学的研究密集型研究生项目之间建立联系，将促进下一代地球科学家的培养。该项目的教育影响将通过与康科德大学的麦克奈尔学者项目密切合作来增强，以促进第一代大学生和弱势群体的科学事业。

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.