Collaborative Research: How does it end? Exploring thrust terminations of an intra-continental strike-slip fault, north Tibet

板块构造理论认为，内部刚性构造板块沿着狭窄的板块边界相互作用。然而，变形往往分布在大陆内部，例如喜马拉雅山脉带东北部的亚洲大陆，那里发生了距离印度板块和欧亚板块边界1000多公里的重大断裂和褶皱。该地区一些最大的地貌是东西走向的走滑断层，如西藏北部的海原断层。该项目研究海原断裂的西端，以确定山带内部从走滑断裂运动到褶皱和逆冲断裂的变形变化。此外，像海原断层这样的构造是亚洲大陆人口稠密地区的主要地震灾害来源。因此，限制沿这些走滑断层长度的变形类型、大小和速率将有助于未来的危险和风险评估。该项目的其他社会相关影响包括：支持职业早期教师建立具有全球竞争力的研究项目；培训一名博士生，并在科学、技术、工程和数学(STEM)学科指导两名本科生；与研究人员和机构进行国际合作；在社区参与活动中扩大对地震灾害的关注。该项目还支持开发一个可供公众访问的现代地质制图网站，该网站提供有关基于数字图板的野外测绘和数字高程模型(DEM)构建的技术和信息，包括将地图数据纳入开放式在线档案的方法。大陆内部对边缘驱动的板块边界条件的反应是大陆构造学的一个中心议题。喜马拉雅-青藏造山带是新生代印度-亚洲渐进式汇聚的产物，造山带内部最大的构造是大型走滑断裂。因此，西藏是确定走滑断裂如何在碰撞造山带中容纳和重新分配应变的理想试验场。这项多学科的调查探索了藏北左滑海原断裂的西端，在那里走滑断裂突然过渡到逆冲断裂。具体地说，结合地质基岩和新构造填图、利用运动构造(SfM)方法建立数字高程模型(DEM)、表面年龄测年(即光激发发光和放射性碳)和低温热年代学，以(1)约束海原断裂带西部的第四纪滑动速率，(2)系统地记录走滑变形如何转移到祁连山冲断带中部的范围-边界-逆冲-断裂系统。利用海原断裂西端运动学野外观测资料，对喜马拉雅-青藏造山带板块会聚-正走滑断裂模型进行了验证，包括(1)顺时针向断层旋转模型、(2)挤压-断层模型和(3)应变传递模型。从研究海原断裂中获得的见解可以应用于其他大陆内变形带。这一裁决反映了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。

Plate tectonic theory suggests that internally rigid tectonic plates interact with one another along narrow plate boundaries. However, deformation is often distributed across the interior of continents, such as in the Asian continent northeast of the Himalayan mountain belt, where significant faulting and folding occurs more than a thousand kilometers from the boundary between the Indian and Eurasian plates. Some of the largest features in the region are east-west oriented strike-slip faults, such as the Haiyuan fault in north Tibet. This project investigates the western termination of the Haiyuan fault to determine how deformation changes from strike-slip fault motion to folding and thrust faulting within the interior of the mountain belt. Furthermore, structures like the Haiyuan fault are sources of major seismic hazards for densely-populated regions within the Asian continent. Thus, constraining the style, magnitude, and rate of deformation along the length of these strike-slip faults will aid in future hazard and risk assessment. Other societally relevant impacts of this project include: support of early-career faculty to establish globally competitive research programs; training a PhD student and mentoring two undergraduates in a science, technology, engineering and mathematics (STEM) discipline; international collaboration with researchers and institutions; and outreach at community engagement events with a focus on earthquake hazards. The project also supports the development of a modern publicly-accessible geologic mapping website that features techniques and information about digital tablet-based field mapping and digital elevation model (DEM) construction, including methods of incorporating map data into open-access online archives.The intra-continental response to edge-driven plate boundary conditions is a central topic in continental tectonics. The Himalayan-Tibetan orogen results from progressive Cenozoic India-Asia convergence, and the largest structures within the interior of this orogen are large strike-slip faults. Therefore, Tibet is an ideal testing ground to determine how strike-slip faulting accommodates and redistributes strain in a collisional orogen. This multidisciplinary investigation explores the western termination of the left-slip Haiyuan fault within northern Tibet, where strike-slip faulting abruptly transitions to thrust faulting. Specifically, a combination of geologic bedrock and neotectonics mapping, construction of digital elevation models (DEMs) using structure-from-motion (SfM) methods, surface-age dating (i.e., optically stimulated luminescence and radiocarbon), and low-temperature thermochronology are employed to (1) constrain Quaternary slip rates along the western Haiyuan fault segments, and (2) systematically document how strike-slip deformation transfers to a range-bounding, thrust-fault system in the central Qilian Shan thrust belt. Field observations of the kinematics of the western termination of the Haiyuan fault are used to test models for plate-convergence-normal strike-slip faulting in the Himalayan-Tibetan orogen, including (1) clockwise-fault rotation, (2) extrusion-fault models, and (3) strain transfer models. Insights gained from studying the Haiyuan fault can be applied to other zones of intra-continental deformation.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.