青藏现今变动三维速度场及大陆板块汇聚变形的运动学

Active deformation of Tibetan Plateau due to the India-Asia collision is distinguished by the nature, amount, style and dynamics that drives this processes. Yet the kinematics of crustal shortening is debated as to its description in terms of either rotations of sub-plates or deforming continuum, and the tectonic evolution in Cenozoic time remains elusive. This proposal concentrates on the present-day shortening across the Himalaya and south Tibet by using geodetic measurements to reveal diffusive deformation characterized by.crustal thickening in the Himalaya and crustal extension in south Tibet. We are planning to refine the surface displacement field in the Tibetan Plateau through adding substantially new GPS sites and using InSAR imagery. Based on the intensified 3D velocity field, we will constrain the block model covering the Tibetan Plateau and its neighboring regions to distinguish various styles of deformation and reveal dynamic aspects. Furthermore, we are able to construct a 3-D strain model for the Main Himalaya Thrust, which sheds insights into.stress-building along the Himalayan arc and strain-partitioning from the crustal shortening on the southern edge of Tibetan Plateau to the crustal thinning in its interior. In doing this, 1) we will process GPS data mostly from “Crustal Movement Observation Network of China” (CMONOC) and reprocess the data collected in the past decades. In order to expand coverage of the existing networks and increase site density, we are planning to supplement 80 campaign sites in south Tibet, and remeasure 150 campaign sites distributed in the entire plateau. We will analyze the archived SAR images acquired by ERS-1/2 and ENVISAT as well as the following-on satellites, from which the surface uplift of Tibet can be extracted when InSAR line-of-sight changes and GPS displacements are combined. we will invert slip rates of active faults from surface displacements to explore fault geometry and mechanics. By simulating the geodetic data using finite element method, we try to elucidate the dynamical process in depth and understand the cause that reshaped the tectonics of Tibet in mid-Miocene. In final, we try to detect transient signals from time series of GPS position to demonstrate stress transfer from the Tibetan Plateau to the Himalaya. In general, our study aims to clarify how the continental tectonics differs in kinematics from the plate tectonics and provide a dataset to help accessement of seismic hazards in China. In addition, the implement of the proposal will provide some clues to sharpen the CMONOC for a better knowledge about the deforming “the roof of the world”.

青藏高原变形强烈、方式多样、动力复杂，迄今其隆升状态不清，构造演化的运动学模式和驱动机制存疑，板块构造理论对大陆变形的适用性意见不一。本项目以藏中南及喜马拉雅为重点，以现今地壳变动观测为基础，研究弥散型大陆碰撞边界带变形时空过程、构造样式与成因机制。课题围绕青藏现今变形图像及其活动地块边界这两个核心问题，科学目标是实现实测位移场优化升级，以此揭示喜马拉雅挤压增厚变形转换为藏中南的拉张减薄变形的内在联系。研究内容涵盖地表三维位移场合成，活动地块运动模型构建，以及板块边界断层地震变形模拟。研究依托国家重大科学基础设施“中国大陆构造环境监测网络”，以GPS、InSAR和卫星重力为技术支撑，通过多种数据联合反演揭示活动地块几何、运动特征，通过时变过程限定介质的流变性，分析地震危险性，引领“中国大陆构造环境监测网络”运行和发展。

青藏高原具有变形强烈、动力复杂、方式多样特点，在大陆构造研究中占有显著地位，迄今其运动学模式存在重大争议，构造演化的动力机制也认识不足。本项目以藏中南及喜马拉雅地区为重点，以现今地壳变动观测为约束，研究弥散型大陆碰撞边界带变形的时空过程，探讨高原边缘地壳挤压增厚与高原腹地伸展减薄变形的构造样式与成因机制。项目通过加密GPS流动站点并与InSAR变形观测图像融合，优化了藏中南地区现今三维位移场。在此基础上构建青藏高原活动地块的运动模型，基于震间变形的精密水准、InSAR和GPS三维速度，以及2015年尼泊尔特大地震的同震变形，发展了喜马拉雅中段主冲断层的应变模型，约束印度板块挤入西藏的板块边界几何以及断层闭锁分布。 .项目研究在三个方面取得进展: 1）将区域内二维水平形变场升级为三维形变场，形变场的空间分辨率有了明显提升，揭示出不少前所未见的细节特征，为区域变形运动学模型提供更好的约束条件，为深部动力过程研究提供了新思路。 2）基于20年GPS观测的时间序列分析，揭示青藏高原中部现今坍陷、喜马拉雅、喀喇昆仑隆起，而阿尔金祁连山一带保持均衡板块边界的动力驱动仅限与喜马拉雅、藏南一带，青藏中部的变形是由重力驱动，并传到高原东部，导致祁连山，龙门山一带挤压隆升。3）印度板块可能仅延伸到雅鲁藏布缝合一带，且存在一条与板块边界断层平行、近水平的浅部分支断层，与喜马拉雅主冲断层深部滑脱层协同调节印度-欧亚板块的碰撞变形，导致喜马拉雅和藏南地壳增厚。