京西北盆岭构造区现代构造应力场的非均匀特征

京西北盆岭构造区包括延矾、怀涿、蔚广、阳原、灵丘、怀安及张家口多个活动断陷盆地.通过对该区大量活动断层擦痕的测量，利用由断层滑动资料反演构造应力张量的计算方法，获得研究区24个测点的构造应力张量数据；同时利用格点尝试法对研究区两个不同应力分区的中小地震震源机制解进行了分析.依据断层滑动与震源机制解两类资料的分析计算结果，初步给出了研究区现代构造应力场的非均匀特征：延矾盆地区域（B区）断层滑动反演的构造应力张量与震源机制解类型均表现为走滑型，表明该区受控于NEE-SWW向挤压、NNW-SSE向拉张的区域构造应力作用.怀涿、蔚广等盆地所在的山西断陷带北部尾端区域（A区）断层滑动反演的构造应力张量与震源机制解类型以正断型为主，表明怀涿、蔚广等盆地所在的山西断陷带北部尾端区域（A区）受近NNW-SSE向拉张的局部构造作用相对于延矾盆地更为显著.现代构造应力场的非均匀分布反映了京西北盆岭构造的差异特征.

Research on heterogeneity of the present tectonic stress field in the basin-and-range province northwest of Beijing

There are several active fault basins in the basin-and-range province northwest of Beijing,such as the Yanfan basin, Huaizhuo basin, Yuguang basin and so on. Based on the investigation of active faults and the measurements of slickensides in the region we have obtained the parameters of 24 tectonic stress tensors in the basin-and-range province northwest of Beijing using the method of inversion of fault slip data. And then we use the Grid Test Method to calculate 85 earthquake focal mechanism solutions with magnitude less than 4.6 during the years of 1972 to 2006, and we get the average result of the stress field. Combined with the statistic result from the types of focal mechanism solutions and fault slip tectonic stress tensors in two different stress districts,we get the heterogeneous characteristics of recent tectonic stress field in the research region.The result shows that the recent tectonic stress field in the basin-and-range province northwest of Beijing is characterized by NEE-SWW maximum compressional stress and NNW-SSE minimum extensional stress, and the stress regimes are all of strike slip. It indicates that a tectonic stress field of near EW compression and near NS extension controls the research region. However,there are some differences between stress districts A and B, that is, the type of focal mechanism solutions and fault slip tectonic stress tensors in Yanfan Basin is strike slip type,but it is normal type in Huaizhuo Basin, Yuguang Basin and other basins.It reflects that compared with Yanfan Basin,the local NNW-SSE extensional stress is more distinct in Huaizhuo and other basins at the north end of Shanxi graben system, where there is a developing extensional tectonic fault zone. And this heterogeneity of the present tectonic stress field reflects the nuance in the basin-and-range province northwest of Beijing.