阿尔金断裂带中段运动特征与应变分布模式研究

As the northern boundary of the Qinghai-Tibet Plateau, the Altyn Tagh fault zone controls the geometrical features and basic tectonic framework of the northern Plateau, and is a very important large strike-slip fault. The study of the structural geometry and slip rate of the boundary faults is the key problem to understand the tectonic evolution history and tectonic deformation process of the Qinghai-Tibet plateau since Cenozoic. The project is to take the middle part of the Altyn Tagh Fault zone as the research area, using the SAR data from different satellite platforms, and using multidimensional time-series InSAR technique to obtain the two-dimensional deformation（vertical and lateral）monitoring results. In this project, the strike slip rate and uplift rate of the middle section of the Altyn Tagh Fault zone are studied, and the coupling relationship between the strike slip and the thrust action of the active fault in the study area is discussed. The GPS observation in the middle section of the Altyn Tagh fault is combined with the time series observation data. According to the structural geometry of the middle part of the Altyn Tagh fault zone and the geophysical deep detection result, the boundary element fault model is established, and the locked depth, the horizontal strike slip rate, the vertical uplifting rate and the creeping velocity distribution on the fault plane are retrieved by Bayesian inversion method, Then the strain accumulation, distribution and seismic risk in the middle section of the Altyn Tagh Fault zone are evaluated.

阿尔金断裂带作为青藏高原北部边界，控制了高原北部的几何学特征及基本的构造框架,是一条非常重要的大型走滑断裂。而边界断裂的构造形态与滑移速率研究更是理解青藏高原新生代以来的构造演化历史和构造变形过程的关键问题。本项目拟以阿尔金断裂带中段为研究区，利用不同平台来源的SAR数据,采用多维时序InSAR技术获取东西向及垂向二维时序形变监测结果。研究组成阿尔金断裂带中段各分段的走滑速率和抬升速率，探讨研究区活动断裂走滑作用与逆冲作用的耦合关系。以时序观测数据为约束，联合该地区跨阿尔金断裂中段GPS观测,根据阿尔金断裂带中段构造几何形态及地球物理深部探测结果，建立边界元断层模型，采用贝叶斯方法反演断裂的闭锁深度、水平走滑速率、垂直隆升速率及震间蠕滑速率分布等，进而对阿尔金断裂带中段应变积累及分布情况、地震危险性进行评估。

阿尔金断裂带作为青藏高原的北部边界，控制了高原北部的几何学特征及基本的构造格架,是一条非常重要的大型走滑断裂。而边界断裂的构造形态与滑移速率研究更是理解青藏高原新生代以来的构造演化历史和构造变形过程的关键问题。项目执行四年来，一直围绕这一关键问题开展工作，主要结果包括：1）采用多维时序InSAR技术获取了阿尔金断裂带东西向及垂向二维时序形变监测结果，显示阿尔金断裂虽以走滑运动为主（~10mm/yr），但伴随着少量的逆冲运动，且从西到东逆冲分量逐渐增大，到阿尔金山地区可达1mm/yr。2）建立模型对组成阿尔金断裂带中段组合构造（北东东向的阿尔金断裂、北东向的北阿尔金断裂）走滑与逆冲作用的耦合关系进行了研究，以时序观测数据为约束，联合该地区跨阿尔金断裂中段GPS观测,贝叶斯方法反演断裂的闭锁深度、水平走滑速率、垂直隆升速率等，结果显示走滑速率(Vss)为10.2 mm/yr，缩短速率为1.2 mm/yr；青藏高原的推挤作用沿NATF转换为阿尔金山的隆升，速率为0.4mm/yr，走滑过程中一部分能量转化为分支的逆冲断裂，逆冲作用使得山体抬升。3）跨阿尔金断裂的形变剖面数据表明地表形变场跨断裂存在非对称的现象，建立粘弹性模型，断层两侧的介质分为弹性上地壳，粘弹性的下地壳和上地幔，采用分层和横向不均匀的介质参数。由水平速率场从西到东两个剖面为约束利用贝叶斯方法反演，综合模型的四种不同参数的组合测试结果，及前人对青藏高原周边弹性层厚度的研究成果，我们认为断层两侧弹性层厚度和剪切模量的差异共同造成了阿尔金在震间形变场不对称现象。