鲜水河断裂带中段雁列断裂活动特征及其形成机制

Characteristic right-step echelon faults have been developed along the central Xianshuihe Fault Zone, on the eastern Tibetan Plateau. Knowledge on activity characteristics of echelon faults is essential for the understanding of the dynamics of strike-slip fault zones as well as regional tectonic deformation. In this research, the segmentation and activity of the echelon faults along the central Xianshuihe Fault Zone will be studied based on quantitative geomorphological analysis method. Geometry and topographic deformation of the echelon faults will be analogized in sandbox. According to detailed interpretation and field investigation of the active fault traces in the study area, Structure from motion (SfM) photogrammetry technique will be utilized to obtain topographic data of characteristic segments to analyze geometry of each fault. Slip rate will be calculated according to the dating of offset landforms. Scaled sandbox models will be designed to simulate the development of echelon faults under various tectonic stress fields. Based on comprehensive studies on the activity characteristics and formation mechanism of the echelon faults in the study area, understanding to the dynamics of the Xianshuihe Fault Zone and the tectonic evolution of the eastern Tibetan Plateau could be improved.

青藏高原东部鲜水河断裂带中段发育典型的右列雁列断裂。雁列断裂的活动特征为揭示走滑断裂带动力学特征及区域构造变形特征提供了良好的研究对象。本项目拟利用定量地貌学分析手段对鲜水河断裂带中段雁列断裂的分段活动特征进行研究，并利用砂箱实验对雁列断裂的几何形态和地表变形特征进行模拟。在对活动断层分布进行详细解译和野外调查的基础上，利用Structure from motion（SfM）摄影测量技术获取研究区典型部位的地形数据，分析各雁列段的几何学特征；对错断地貌体进行测年，计算各雁列段的滑动速率；利用砂箱实验装置建立适当的比例砂箱模型，对不同构造应力背景下雁列断裂的发育进行模拟。通过对研究区雁列断裂活动特征及其形成机制的综合研究增强对鲜水河断裂带动力学特征及青藏高原东部构造演化特征的认识。

鲜水河左行走滑断裂带是中国一条重要的发震走滑断裂带，历史上有多次大地震记录。其中段发育雁列断裂，为古地震复发规律研究增加了难度，同时也为其动力学演化机制提供了突破口。通过利用高精度卫星影像和DEM数据对研究区的活动构造地貌和活断层行迹进行解译并开展野外调查，获得了鲜水河断裂带中段色拉哈断层和折多塘断层的详细断层分布，发现色拉哈断层也存在分段性，中段具有走滑拉张活动特征。通过对色拉哈断层错断地貌进行分析和取样测年，厘定了色拉哈断层和折多塘断层晚第四纪以来的走滑速率。根据被错断末次冰川期以来冰碛堤的位错量估算色拉哈断层北段走滑速率为5.6 mm/yr，通过对被错断河流地貌进行测量和放射性碳素测年，获得色拉哈断层南段和折多塘断层的走滑速率分别为3.4 mm/yr和10 mm/yr。其中呈雁列关系的色拉哈断层北段和折多塘断层共同分担了10 mm/yr的总走滑速率。通过调查折多塘断层的详细分布，我们发现了1955年折多塘地震的同震地表破裂，同时还发现了新的断层分支及其活动痕迹，结合野外测得的同震位错量分布，重新估算1955年折多塘地震的震级为Mw 7.0。在对鲜水河断裂带中段雁列断裂详细认识的基础上，通过砂箱物理模拟实验对走滑断裂带雁列断裂的演化过程进行了模拟分析，表明雁列断裂是走滑断裂贯穿过程中的重要阶段。