Abstract: This paper mainly studies the distribution of structural deformation and stress under the motion of thrust fault due to the effect of stress normal to the strike direction. As an example,we build the finite element model of central fault of Longmen Shan Fault zone,the Yingxiu-Qingchuan Fault. The finite element model is the model of single inverse fault. During the study,we compute the variations of surface deformation and stress fields near to the fault due to the thrust motion of Yingxiu-Qingchuan Fault in the process of Wenchuan earthquake. In the computation,we apply the frictional contact element and curved surface geometry to simulating the fault plane to obtain the variations of stress components and displacement field which are normal to strike direction and ground surface. In order to get the stress value of the hanging fall of the Yingxiu-Qingchuan Fault,we also apply the static dislocation model to the computation. Through the computation,we find that the displacement field along the strike direction can exist even if there is no initial stress load along the strike,but the value of this deformation is tiny. So we believe the displacement field along the strike may stem from the transverse deformation due to the extrusion of thrust fault; The structure deformation normal to the strike direction resulting from the thrust motion of inverse fault does not reach to maximum value at the zone near the fault,but the structure deformation normal to the ground surface can reach the maximum at the zone near to the fault; Generally,under the compression stress effect,the amount of crustal shortening is much bigger than that of uplift deformation at the zone near to the inverse fault,and the value of compression stress is much bigger than that of stress normal to ground surface along the fault plane. Furthermore,variation of stress on the inverse fault plane occurs mainly at the area where the dip angle of fault plane changes.

Key words: Longmenshan Fault, surface deformation, finite element method, dislocation model

摘要： 为了研究逆断层受到垂直于断层走向的应力作用下发生逆冲构造运动时造成的变形以及相应的应力场分布，以龙门山中央断层映秀—青川段为例建立了逆冲断层的有限元模型。该模型为单个逆冲断层有限元模型，计算了汶川地震过程中龙门山中央断层逆冲错动引起的地表变形场和断层附近应力场的变化。模拟中对断层面采用的是摩擦接触单元，且断层面设为曲面的几何形状；模拟给出断层错动形成的地表沿垂直走向和垂直地表的变形以及相应的应力分量场的变化情况。为得到计算模型边界处的应力值，采用了断层静态位错模型进行计算。结果发现，在不施加沿断层走向的载荷时，沿断层走向上存在变形，这可能是断层在受到挤压后发生的横向变形，但该变形较小；逆冲断层构造运动引起沿垂直断层走向方向上的变形并不是在近断层处达到最大，而是沿垂直地表向上的变形在断层处达到最大；逆冲断层在挤压构造应力下的变形要大于逆冲构造附近的隆升变形，同时断层面上的挤压应力大于垂直地表方向的应力；断层面上的应力场沿断层面的变化主要集中在断层面倾角发生变化以及震源区域附近。

关键词: 龙门山断层, 地表变形, 有限元, 位错模型