NUMERICAL SIMULATION OF LONG-TERM DEFORMATION OF TIBETAN PLATEAU AND SURROUNDING AREA

doi:10.3969/j.issn.0253-4967.2016.02.014

Abstract

Abstract:

The subduction of the Indian plate underneath Eurasian plate results not only in deformation and movement of the elastic upper crust, but also flow of the ductile lower crust in the high temperature and high pressure which drags the brittle upper crust to move at the same time. These two actions work together producing the present movement and deformation field in Tibetan plateau. The dynamics progress has been verified by GPS observation data. Therefore, in a two-dimension plain model, only the elastic deformation with the boundary action at the upper crust cannot explain the deformation well, the drag force acted on the base of upper crust by the drag of ductile flow of the lower crust also need to be considered. However, it's hard to figure out the magnitude and direction of the drag force. Thus, we established a two-dimension plain elastic finite element model, with the equivalent-body force approach to simulate the drag force. With the internal GPS observation data of Tibetan plateau as constraint condition, we calculated inversely the drag force of key nodes in the model with trial method, and the other nodes in the model with bilinear interpolation method. Finally, we got the drag forces(nodal forces, unit:N) caused by the difference flow of ductile lower crust dragging the brittle upper crust, which are distributed mainly in the region of 86°~100°E and 26°~32°N, the direction is east and south, and the maximum reaches to 1e8N; in some areas in the western part of the study region at 31°~36°N and 76°~80°E, the direction is west, and the maximum reaches to 1e7N. All these work provides a new thought for further research on long-term dynamic mechanism of surface deformation in Tibetan plateau and its surrounding area.

Key words: finite element method, numerical simulation, Tibetan plateau, drag forces, bilinear interpolation

摘要：

印度板块向欧亚板块俯冲挤压，不仅令青藏高原上地壳在挤压作用下发生弹性变形和运动，且青藏高原高温高压下的下地壳会发生柔性流动，并对脆性的上地壳有拖曳作用，这2种作用一起形成现今的高原运动变形场。这一动力学过程已得到GPS观测资料的证实。因此在二维平面问题中仅用上地壳在边界作用下的弹性变形解释是不够的，还要考虑柔性下地壳流动对上地壳的拖曳作用。但是拖曳力作用的大小和方向不易确定，故文中建立了二维平面弹性有限元模型，利用加载等效体力来模拟下地壳流动对上地壳产生的拖曳力。以高原内部的GPS观测资料为约束，利用试错法反演出模型中关键点的力，其他位置上的力则用关键点上的力进行双线性插值计算。以此来反演计算出模型区域内的柔性下地壳的差异性流动对脆性上地壳产生的拖曳力（节点力的形式，单位：N）的大小和范围，在86°～100°E，26°～32°N地区主要以SE向为主，最大达到10⁸N；西部局部（31°～36°N，76°～80°E）地区有较弱的W向拖曳力，最大为10⁷N。文中为深入研究青藏高原及周边区域的长期地表变形动力学机制提供了1个新的思路。

关键词: 有限元, 数值模拟, 青藏高原, 拖曳力, 双线性插值

CLC Number:

P315.2

DONG Pei-yu, HU Cai-bo, SHI Yao-lin. NUMERICAL SIMULATION OF LONG-TERM DEFORMATION OF TIBETAN PLATEAU AND SURROUNDING AREA[J]. SEISMOLOGY AND GEOLOGY, 2016, 38(2): 410-422.

董培育, 胡才博, 石耀霖. 青藏高原及周边区域地表长期变形数值模拟[J]. 地震地质, 2016, 38(2): 410-422.

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