青藏高原地壳水平差异运动的GPS观测研究

HORIZONTAL CRUSTAL MOVEMENT OF TIBETAN PLATEAU FROM GPS MEASUREMENTS

以青藏高原及其周边 5 80多个GPS站点的观测资料为基础 ,通过消除青藏高原的整体刚性运动 ,将GPS水平速度场归化到“青藏高原整体固定”的参考框架下 ,使青藏高原内部不同区域的水平差异运动得以获得最大限度的突出。所得速度场图像显示 :①以玛尼 玉树 鲜水河断裂为界的青藏高原东南部区域 ,最突出的内部水平形变表现为一条绕喜马拉雅东构造结的挤出式顺时针“流滑带”。而这一流滑带前缘速度场在青藏高原东南角呈现扇形发散特征 ,表明整个流滑带起因于高塑性上地壳物质在挤压和重力共同作用下的侧向逃逸 ;②介于玛尼 玉树 鲜水河断裂和海原断裂之间的青藏高原东北部区域 ,总体上表现出比较均匀的左旋剪切带特性 ,但这种左旋剪切在青藏高原东缘的龙门山一带已不再明显 ,且四川盆地及其以北区域 ,并未承受强烈挤压。因此 ,青藏高原东北部区域 ,相对于高原整体 ,并无明显的东向逃逸。③在整个青藏高原区域内 ,阿尔金断裂、海原断裂及玛尼 玉树 鲜水河断裂两侧的速度场显示了明显的差异 ,反映出这三条断裂带现今强烈的活动性。由于位于玛尼 玉树 鲜水河断裂和喀喇昆仑 嘉黎断裂之间的塑性流滑带的独立东向“逃逸”所产生的“拖拽”使流滑带以北区域表现为整体均匀的左旋剪切 。

Using the measurements of over 580 GPS stations located around the Tibetan plateau,we derive a spatially dense horizontal velocity field of the region.In order to better visualize the differential motion among stations within the plateau,we transform the velocity field into a “Tibetan plateau fixed reference frame”.The velocity field shows that:①For the southeast region of the plateau bounded by the Mani Yushu Xianshuihe fault the most remarkable horizontal movement is a clock wise“flow zone”around the Eastern Himalayan Syntaxis.The velocity field of the “flow zone”has a fan like shape in the southeastern corner of the plateau,implying that the “flow zone”could be attributed to the escape of a high plastic upper crust material driven by the lateral compression and gravitational buoyancy.②The northeastern region of the plateau located between the Mani Yushu Xianshuihe fault and the Haiyuan fault appears to be a uniform left lateral shear zone overall.However,such a shear deformation is not significant in the Longmenshan area along the east margin of the Tibetan plateau.The Sichuan basin and its northern neighborhood region do not accommodate significant shortening either.Therefore,the northeastern region of the Tibetan plateau does not show significant eastward motion with respect to the rest part of the plateau.③The most significant velocity gradients within the plateau exist across the Altyn Tagh,Haiyuan,and Mani Yushu Xianshuihe faults,reflecting extensive activities there.Because of the “dragging”associated with the eastward escape of the plastic flow zone between the Mani Yushu Xianshuihe fault and the Karakunlun Jiali fault,the north and south regions of the flow zone display left and right lateral shear respectively.