Active tectonics of the Pamir Mountains: kinematics and dynamics

控制大陆内大规模活动变形的规则，以及地震期间活动断层上的滑动调节构造运动的方式，都是一级问题，许多模型是根据对印度-欧亚碰撞带的观察而建立的。在印度/亚洲碰撞中，大约30毫米/年的会聚分布在南北绵延数千公里的区域[1-3]。因此，单个断层的移动非常缓慢(约1毫米/年)，地震重复次数可达数千年[3]。这意味着对于喜马拉雅冲断以北的大多数断层来说，过去事件的时间、频率和震级都是未知的。中亚的地震数据记录始于1901年[4]，此后在塔吉克斯坦采集了四次大地震(&GT；M7)，其中三次发生在帕米尔地区[5]-[9]。然而，更新世/全新世破裂的地貌证据在其他地方表明这一记录是不完整的[10]。帕米尔高原是印度-欧亚碰撞西部构造带上的低起伏高原，由一套跨越中、新生代的复杂地体组成[11]。它是一个陆内俯冲的地点，在其北部和南部边缘[12][13]，并正在经历向西的重力塌陷进入邻近的塔吉克盆地[1]。尽管GNSS数据显示南北汇聚速度很快，但发生在帕米尔地区的大部分应变似乎是东西走向的[14][2][15]。此外，帕米尔群岛西部似乎比东部帕米尔地区有更多的东西向应变[1]。内部变形被认为是相对较少的主要断层，包括利用地体缝合线的东西走向的逆冲/走滑断层，被两个南北走向的走滑/正断裂带切割[16][17][10]。这组丰富的行为取决于作用在帕米尔高原上的外力、地形上的重力、脆性岩石圈中断层的阻力和/或韧性岩石圈的粘性。它们还依赖于帕米尔高原建成时形成的继承性地质结构。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。这将使用GNSS应变测量、断层长期平均滑动速率的测量以及对其滑动矢量的了解来完成。研究这些断层上的大地震给我们提供了提取其滑动速率和滑动向量的最佳机会，并将提供与地震危险性评估有关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，除了在现有地质图上编目更大规模的偏移量外，研究最近的地表破裂和偏移标记物(使用放射性碳或光激发发光[18])将是必要的。目的和目的本项目的目的是描述帕米尔高原主要断裂上的运动特征，并利用这些数据来深入了解该地区的地震灾害和构造运动学，这两者都是鲜为人知的。然后我将尝试解释为什么我们观察到这种运动学行为，以及它如何依赖于该地区的地质结构和力量。

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.