西藏中部申扎—定结地堑系北段中新世以来构造地貌学研究

利用ETM遥感影像与30 m分辨率的ASTER DEM数据, 构建申扎—定结地堑系北段遥感影像三维数字高程模型, 结合野外地质地貌调查结果, 对地堑系地貌特征进行总体分析。并根据对主要断裂的产状和活动性野外调查与活动断裂展布的遥感解译结果, 认为地堑系由一条东倾的铲式主要断裂和一系列同倾向和反倾向的次级断裂组成的半地堑构造。基于半地堑系模式, 将地堑系简化成书斜式模型, 根据地堑的沉降量和地堑宽度值, 计算地堑系的滑脱面深度在3.6～9.7 km之间, 因此地堑中地震震源深度也多集中于滑脱面附近。最后探讨地堑的形成机制, 表明在印度板块的挤压作用下, 高原上地壳与下地壳发生应力解耦, 上地壳在重力作用下, 向南向东发生滑脱, 形成东倾的半地堑构造。

Tectonic Geomorphology of the Northern Segment of Shenzha-Dingjie Graben since Miocene in Middle Tibetan Plateau

ETM remote sensing image and 30 m resolution ASTER DEM data are treated using ArcGIS, and three-dimensional digital elevation model of the northern segment of Shenzha-Dingjie graben with remote sensing image is built, combined with field investigattion, the overall of landscape characteristics of the graben is analysised. On the base of field observation of the main faults, as well as the spreading of graben′s fault from remote sensing interpretation, we found that the faults in half-graben is composed by a east dip major fault with a series of synthetic sub-faults and antithetic sub-faults. Based on half-graben system model, a simple book oblique model is used to calculate the depth of detachment surface and the magnitude of stretch in the graben system. The depth between 3.6~9.7 km is basically consistent to the focal depth in the region, which prove that seismic activity concentrated in the vicinity of the detachment surface. Finally, the graben formation mechanism is discussed. The stress of upper crust is decoupled with lower crust′s due to Indian plate extrusion, and the upper crust moves south and east from gravity, thus the half-graben dip east.