Abstract: Based on the seismic and geologic information available, North Qilian and Hexi Corridor area is divided into a number of 3-D finite elements. On the assumption of linear elastic model, the general tendency of vertical deformation spanning about 20 years in this area is simulated. The simulated results of this area bear a close relation with boundary condition and variation of background stress field. Among them, the result obtained by taking the increment of tectonic stress field as loading condition and stable block as displacement boundary condition, is in good consistence with the general distribution of vertical deformation in this area in the past 20 years. Based on this acknowledgement, the increment of the background stress field is estimated. The pressure change along N-S direction is +0.11MPa, and that along E-W direction is +0.04MPa (compressive pressure is positive). The quantity of the pressure change along E-W direction is three times of that along N-S direction. In addition, by comparing the distribution character of the obtained incremental shear stress (Δγ_xy) field with that of the foci of mid strong earthquakes, we find that there is a certain relationship between the incremental shear stress and the location of these earthquake foci. The fact that the earthquake focus is usually located in the area of severe variation of shear stress increment proves that the simulated tectonic stress field is reasonable to some extent.

Key words: vertical movement, 3-D finite element method, tectonic stress field, shear stress increment

摘要： 根据已知的地震地质资料对北祁连-河西走廊及相邻区进行了三维有限单元剖分,在线弹性条件下,拟合了其20a来垂直运动的总体趋势。计算表明,北祁连-河西走廊地区垂直形变的拟合结果,与背景应力场的约束形式和变化特征密切相关,其中采用构造应力场增强作为加载条件以及稳定地块作为位移约束条件得出的拟合结果与该区域20a来垂直运动的整体分布特点相一致。在此基础上,进一步得到其背景应力场增强的量值估算,其中SN方向的压力变化为+0.11MPa(压为正),EW方向的压力变化为+0.04MPa(压为正),EW方向的压力变化量是SN方向的3倍左右。此外,根据计算得到的10～15km深处剪应力增量Δγ_xy的分布情况,对比中强地震震源分布可以看出,剪应力增量与震源在空间分布上有一定的关联性。震源往往分布在剪应力增量变化较剧烈处,从而证实了拟合得出的构造应力场具有一定的合理性。

关键词: 垂直运动, 三维有限单元, 构造应力场　剪应力增量