Abstract: The Zhangjiakou-Bohai fault zone in the northern part of North China area is a seismotectonic zone controlling the present-day strong earthquake activity. Under the effect of NEE-directing regional principal compressive stress,a series of NE trending active tectonic zones were engendered in this area. Together with the Zhangjiakou-Bohai fault zone,they make up a group of conjugate shear fracturing systems,controlling the occurrence of the present-day strong earthquakes. This paper focuses mainly on the feature of crustal deformation around this fault zone. The secular GPS crustal deformation image has reflected the relatively complete left-lateral strike-slip movement of this active fault zone. However,the crustal deformation images of different stages indicate that a series of NE-trending large-scale anomalous gradient zones appeared along the Zhangjiakou-Bohai zone before the occurrence of moderate strong earthquakes. These anomalous zones have indicated separately the activities of the Tangshan-Hejian,Sanhe-Laishui and Yan-huai-Shanxi seismotectonic zones,and represented the medium term precursors of the moderate strong earthquake along the Zhangjiakou-Bohai fault zone. Furthermore,the results of this study suggest that the crustal deformation that appears before the occurrence of strong earthquake reflects the strain activity in the deep seismogenic zone,while the disorderly and unsystematic crustal deformation images that occur after the occurrence of strong earthquake reflect the adjusting movement of the covering strata.

Key words: Zhangjiakou-Bohai seismotectonic zone, crustal deformation, NE-trending gradient zone

摘要： 华北北部地区的张家口-渤海断裂带是控制现代强震的一条地震构造带。新近纪以来,在区域NEE向主压应力的作用下,新发育了一系列的NE向构造活动带,与张家口-渤海断裂带组成1组共轭的剪切破裂系统,控制了近代强震的发生。文中主要探讨了这条断裂带的地壳形变特征。长趋势GPS地壳形变图像反映了这条活动断裂带相对完整的左旋走滑活动。分期的地壳形变图像揭示了在中强地震前,沿该断裂带出现一系列的NE向梯度异常带,分别指示了唐山-河间、三河-涞水以及延怀-山西地震构造活动带的活动,表明了沿张家口-渤海断裂带出现了中强地震的中期前兆。研究认为,强震前地壳形变揭示的是深部蕴震层的应变活动信息,而强震之后比较杂乱的图像特征体现了盖层的调整运动。

关键词: 张家口-渤海地震构造带, 地壳形变, NE向梯度带