用GPS资料研究华北地区形变场和构造应力场

利用华北地区地质构造、第四纪以来的活动断层、地形、地壳厚度、地壳及上地幔地震波速度结构等资料,构建了三维有限元框架模型,利用最新GPS观测结果作为边界约束条件,模拟计算了华北地区的形变场及构造应力场。结果表明,模型预测地表速度场和GPS观测结果比较一致。模拟结果中,大型NNE向断层如汾渭地堑断裂系呈右旋运动,NWW向断层如张家口渤海断裂带呈左旋运动,与野外地质考察结果一致。在地表以下10～20km处,模型预测应力场的主压应力方向为NNE、EW向,主张应力大约为主压应力2～8倍。模型中最大剪切应力场在山西、华北平原中部和东部沿海分别出现3条NNE向高梯度带,此梯度带与研究区域的主要地震活动带相对应。

DEFORMATION FIELD AND TECTONIC STRESS FIELD CONSTRAINED BY GPS OBSERVATIONS IN NORTH CHINA

The 3D FEM model of North China was created, which had been incorporated with the data of tectonic, Quaternary active faults, topography, the thickness of crust and crust-uppermantle velocity structure. Having constrained by GPS observations as boundary condition, the deformation and tectonic stress fields were simulated. The calculation result show that the predicted surface velocity field is very consistent with the GPS observations. In these results, large NNE trending faults, such as Fenwei graben fault system, manifest itself of right-lateral slip, and NWW trending fault system, such as Zhangjiakou-Bohai fault system, left-lateral slip, which are in accordance with the results from field geological inspection. For the predicted stress field in the depth of 10-20 km below the earth surface, the direction of the principal compressive stress is NNE-EW, the principal tensile stress is about 3-8 times larger than the principal compressive stress. In the maximal shear stress field, there are three high gradient zones located in Shanxi region, the central North China plain and the coast region of East China, respectively,these zones correspond to main active earthquake zones in the studied region.