Active tectonics of the Pamir Mountains: kinematics and dynamics

帕米尔山脉的活动构造：运动学和动力学

• 批准号: 2284010
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2284010
• 关键词: Active; tectonics; Pamir; Mountains; kinematics

The rules that govern the large-scale active deformation within the continents, and the ways inwhich tectonic motions are accommodated by slip on active faults during earthquakes, are first-order questions, with many of the models established from observations in the India-Eurasia collision zone. In the India/Asia collision, about 30mm/yr of convergence is distributed across a region that is several thousand kilometresin north-south extent[1 -3]. As a result, individual faultscan movevery slowly(order of <1 mm/yr) and have earthquake repeat times on the scale of thousands of years[3]. This means for most faults north of the Himalayan thrust,the timing, frequency and magnitude of past events is unknown.The seismic data record in Central Asia began in 1901[4]and has since sampled four major (>M7) earthquakes in Tajikistan, three of these in the Pamir[5]-[9]. However, geomorphic evidence of Pleistocene/Holocene ruptureselsewhereshows this record is incomplete[10]. ThePamir is alow relief plateau on the western syntaxis of the India-Eurasia collision,composed of a complex set of terranes accreted across the Mesozoic and Cenozoic[11]. It isa site of intracontinental subduction,at both its northern and southern margins [12][13],and is undergoing westward gravitational collapse into the neighbouring Tajik Basin[1].Despite the high north-south convergence velocities in GNSS data, the majority of strain happening in the Pamir appears to be east-west orientated[14][2][15].In addition, there appears to be more east-west strain in the western Pamir than the eastern Pamir[1]. The interior deformationis thought to be taken up by relatively few major faults, consisting of east-west trending thrust/strike-slip faults exploiting terrane sutures, cut bytwo north-south trending strike-slip/normal faultzones[16][17][10].This rich set of behaviours depend on external forces acting on the Pamir;gravitational forceson the topography;and the resistive forces of the faults in the brittle lithosphereand/orthe viscosity of the ductile lithosphere. They also depend on the inherited geologic structuresformed as the Pamir were built. To determine how these structures and forces drive the deformation,the deformation needs to be well characterized. This will be doneusing GNSS measurements of strain, measurements of the long-term average slip rates ofthe faults, and an understanding of their slip vectors. Studyingmajor earthquakeson these faultsgivesus the best chance of extracting their slip rates and slip vectors, and will provide information on magnitude and repeat time, pertinent to seismic hazard assessments. Since most of the major earthquakes will have occurred pre-1901, studyingrecent surface ruptures and dating offset markers (using radiocarbon or optically stimulated luminescence[18]) will be necessary, in addition to cataloginglarger scale offsets in existing geological maps.Aims and ObjectivesThe aim of this project is characterizing motion on major faults in the Pamir Plateau, and using this data to obtain insights into seismic hazard and tectonic kinematics in the region, both of which are poorly understood. I will then attempt to address why we observe this kinematic behavior, and how it depends on the region's geologic structures and forces.

控制大陆内部大规模活动变形的规则，以及地震期间活动断层上的滑动对构造运动的调节方式，都是一级问题，许多模型都是根据印度-欧亚碰撞带的观察建立的。在印度/亚洲碰撞中，大约30mm/年的辐合分布在南北延伸数千公里的区域内[1 -3]。因此，个别断层可以非常缓慢地移动（小于1毫米/年的数量级），并且地震重复次数以数千年为尺度。这意味着对于喜马拉雅逆冲带以北的大多数断层来说，过去地震的时间、频率和强度都是未知的。中亚的地震数据记录始于1901年，此后在塔吉克斯坦进行了四次大地震（>M7）采样，其中三次发生在帕米尔高原[5]-[9]。然而，其他地方更新世/全新世破裂的地貌证据表明，这一记录是不完整的。帕米尔高原是印度-欧亚碰撞西合带上的低凸起高原，由一套横跨中、新生代的复杂地质体组成。它是大陆内俯冲的位置，在其南北边缘b[13]，并正在经历向西向邻近的塔吉克盆地[1]的重力塌陷。尽管GNSS数据显示南北辐合速度很高，但帕米尔高原发生的大部分应变似乎是东西向的[14][2][15]。此外，帕米尔高原西部地区似乎比东部地区有更多的东西向菌株。内部变形被认为是由相对较少的主要断层承担的，由东西向的逆冲/走滑断层利用地缝组成，由两条南北走向的走滑/正断裂带[16][17][10]切割。这一系列丰富的行为取决于作用于帕米尔的外力；地形上的重力；以及脆性岩石圈中断层的阻力和/或韧性岩石圈的粘度。它们还取决于帕米尔高原建成时遗留下来的地质结构。为了确定这些结构和力是如何驱动变形的，需要很好地表征变形。这将通过GNSS测量应变、测量断层的长期平均滑动率以及了解其滑动向量来完成。研究这些断层上的大地震为我们提供了提取其滑动速率和滑动向量的最佳机会，并将提供有关地震危险性评估的震级和重复时间的信息。由于大多数大地震将发生在1901年之前，除了在现有的地质图中编目更大规模的偏移外，还需要研究最近的地表破裂并确定偏移标记的年代（使用放射性碳或光学激发发光[18]）。该项目的目的是描述帕米尔高原主要断层的运动特征，并利用这些数据深入了解该地区的地震危险性和构造运动学，这两者都知之甚少。然后，我将尝试解释为什么我们观察到这种运动行为，以及它如何取决于该地区的地质结构和力量。