Quaternary Activity of Buried Fault in Yanfan Basin

In this paper, we analyze the activity of the buried fault in Yanfan basin on basis of the sedimentary characteristics of Quaternary, combining the results of the multi-electrode resistivity, CSAMT, shallow earthquake and Drilling magnetic susceptibility The results show that the south section of north margin fault of Yanfan basin(buried) extend along Yaowan-Sangyuannanbao village, it consists of two SE tendency step-shaped normal faults and cuts the Nihewan stratum of Quaternary upper Pleistocene. The depth of upper break point is 40 m, and breaking distance is 35 m. It is shown that the activity of the early-middle Pleistocene was active and became stronger in the late Pleistocene. After the Holocene the activity of faults gradually decreased. The buried north section of Shizhuang fault distribute in the SE145°direction, and also cut Nihewan stratum and the depth of upper break point is 70 m, its activity has been high in the early-middle Pleistocene, and become higher in the late Pleistocene. Comprehensive analysis indicate that the buried faults of Yanhuai basin are very active in the late Pleistocene, and then become weaker since the Holocene.