Abstract:An active fault leads to disaster in the world, and within the general development of disasters, an active fault's frequency and the damage it causes is based on the degree of the fault layer, and gradually intensifies. In recent years, earthquake prediction research and engineering construction developments have vigorously promoted the study of active faults. The Zhangjiakou-Xuanhua Basin, situated in the intersection of the Zhangjiakou-Bohai fault zone and the Shanxi seismic tectonic zone, is a typical Cenozoic extensional fault-depression basin. There are many active faults in this basin, which control the basin's development and evolution. However, there is scant research on the active faults in the Zhangjiakou-Xuanhua Basin, and existing research is confined to a few areas. As such, a systematic analysis of this area's active faults, the identification of quantitative information regarding active faults, and a better understanding of the characteristics of this basin's long-term activity is important in theory and practice. Based on an analysis and reorganization of relevant information from detailed field investigations and shallow seismic exploration, this study describes the geometric characteristics and tectonic activities of the active faults in the Zhangjiakou-Xuanhua Basin. The faults for which there are research data include the Zhangjiakou, Wanquan, Ximalin-Shuiquan, and Yanghe faults. The results showed that:The Zhangjiakou fault strikes mainly to the northwest and east-west, dipping to the north, and extending over 70 km. As a major geological and geomorphologic boundary, the Zhangjiakou fault controls the geotectonic movement in this region, in which its southern side is characterized by Late Quaternary unconsolidated basin deposits, and its northern side by Mesozoic volcano debris and Pre-Mesozoic metamorphic rocks in the form of lower mountains and hills. The Zhangjiakou faults are mainly high-angle inverse strike-slip faults with some normal strike-slip faults. The activity of the central segment of the Zhangjiakou fault is stronger than that in other segments. Since the late Pleistocene, the average vertical slip rate along a single fault is over 0.07~0.30 mm/a, while the total vertical slip rate over the entire fault is as high as 1.33 mm/a. The Wanquan fault lies in the northwest of the Zhangjiakou-Xuanhua Basin, striking mainly northeast or north-northeast, dipping southeast, and extending over 15 km. It is a major geological and geomorphic margin, controlling the neotectonic movement in this region. On the southeast side of the Wanquan fault there are Late Quaternary unconsolidated deposits, forming a basin or deposition; but on the other side there is Mesozoic volcano debris, forming lower mountains and hills. The Wanquan fault is a normal fault with southeast-dipping at a medium-high-angle. This fault was active in the Quaternary. Since the middle-late time of the late Pleistocene, the average rate with vertical slip of a single fault has been about 0.03~0.3 mm/a, but the fault has multiple slipping surfaces, and a total large-rate with vertical slip is yet to be estimated. The Ximalin-Shuiquan fault is located in the southwest of the Zhangjiakou-Xuanhua Basin, and can be divided into four sections. The fault strikes mainly northwest, with high-angle inverse strike-slip fault or normal strike-slip fault characteristics. The latest active time of the Ximalin-Shuiquan fault is in the late Middle Pleistocene. The Yanghe fault is a subsurface fault, and its active time was in the Middle Pleistocene. The fault strikes mainly northwest, and controlled the Yanghe River's flow direction and terrace development. The fault strikes mainly northwest, with high-angle slip fault characteristics.