Acta Scientiarum Naturalium Universitatis Pekinensis

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Genetic Algorithm-Finite Element Inversion of Topographic Spreading Forces and Drag Forces of Lower Crust to Upper Crust in Tibetan Plateau

ZHU Shoubiao1,   

  • Received:2004-03-15 Online:2005-03-20 Published:2005-03-20



Abstract: Based on the data of focal mechanism, the boundary forces, topographic spreading forces and shear forces applied beneath the upper crust are inversed by pseudo-3D genetic algorithm finite element method (GA-FEM) in Tibetan Plateau (72°E-105°E,25°N-41°N). The inversion method of topographic spreading forces is analyzed, and reliable result is obtained. The result shows that the collision between India and Eurasia plates plays a dominant role in forming the stress field in Tibetan Plateau, basal drag forces applied by the lower crust to the upper crust and topographic spreading forces on the margin of Tibetan plateau are also significant factors in forming the stress field. However, significant shear forces are not found beneath the area in Tarim and Qaidam basins. The model displacements inversed from stress field agree with present displacements measured by GPS, showing the result is reasonable, and the present tectonic movement reflected by GPS inherits the long period trend of geological movements.

Key words: inversion of GA-FEM, topographical spreading forces, drag forces, Tibetan Plateau

摘要: 利用震源机制解等资料,运用伪三维遗传有限单元法反演了青藏高原 (72°—105°E,25°—41°N)受到的边界作用、地形扩展力以及该地区底部所受的剪切作用力。对高原地形扩展力的反演方法进行了分析,获得了稳定的反演结果。结果显示,印度洋板块的挤压碰撞对青藏高原应力场起着决定性作用, 高原东部下地壳对上地壳的拖曳和高原边缘处的地形扩展力也有显著影响,高原北部的塔里木盆地和柴达木盆地所在区域的上地壳底部未发现有显著效果的拖曳力。从应力场反演的模型位移与GPS实测的现今位移资料也大体吻合,不仅反映结果有合理的物理意义,也说明现今地壳运动与较长期的地质活动有一定的继承关系。

关键词: 遗传有限单元法反演, 地形扩展力, 拖曳力, 青藏高原

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