Active tectonics of the Pamir Mountains: kinematics and dynamics

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-欧亚碰撞带的观测建立的。在印度/亚洲碰撞中，约30 mm/年的辐合分布在南北数千公里的区域[1 - 3]。因此，个别断层可能移动非常缓慢（数量级<1 mm/年），地震重复次数可达数千年[3]。这意味着喜马拉雅山逆冲断层以北的大多数断层，过去地震的时间、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样了四次大地震（> 7级），其中三次发生在帕米尔[5]-[9]。然而，更新世/全新世断裂的地貌证据表明，这一记录是不完整的[10]。帕米尔高原是印度-欧亚大陆碰撞构造结西部的低起伏高原，由一套复杂的中、新生代增生岩系组成[11]。它伊萨陆内俯冲的场所，在其北方和南部边缘[12][13]，并且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数据显示南北向的收敛速度很高，但帕米尔发生的大部分应变似乎是东西向的[14][2][15]。此外，西帕米尔的东西向应变似乎比东帕米尔大[1]。内部变形被认为是由相对较少的主要断层所占据，包括东西走向的逆冲/走滑断层，利用了断层缝合线，被两个南北走向的走滑/正断层带切割[16][17][10]。这种丰富的行为取决于作用在帕米尔的外力：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。它们也依赖于帕米尔高原建成时所继承的地质结构。为了确定这些结构和力如何驱动变形，需要很好地表征变形。这将通过使用GNSS测量应变、测量断层的长期平均滑动速率以及了解其滑动矢量来完成。研究这些断层上的大地震，使我们有最好的机会提取它们的滑动速率和滑动矢量，并将提供有关地震危险性评估的震级和重复时间的信息。由于大多数大地震都发生在1901年之前，研究最近的地表破裂和确定偏移标记的年代（使用放射性碳或光激发发光[18]）将是必要的，除了编目现有地质图中较大比例尺的偏移。目的和目标本项目的目的是表征帕米尔高原主要断层的运动，并利用这些数据来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，我将试图解决为什么我们观察到这种运动学行为，以及它如何取决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.