Application of comprehensive geophysical-drilling exploration to detect the buried North Boundary active Fault Belt of Yanqing-Fanshan Basin in Sangyuan town, Beijing-Zhangjiakou area

North Yanqing and Fanshan Basin active fault is a significant factor for engineering design of Beijing-Zhangjiakou highspeed railway, and buried section of this active fault in Yanqing and Fanshan Basin is complicated and unclear. In order to detect the location, characteristics and activity intensity of the buried active fault, the authors used many methods, such as the controlled source audio-frequency magnetotelluric (CSAMT), shallow seismic reflection, high density resistivity and drilling exploration. The results show that the buried North Yanqing and Fanshan Basin active fault consists of two secondary faults, i.e., F2-1, F2-2, which are distributed parallelly. The trending of the tow secondary faults is N56°E, and the dip angle of them is 50~70°. Meanwhile, they are right-stepped, oblique-arranged normal faults. The burial depth of distinguishable broken point is 10m for F2-1 secondary fault and 30m for F2-2 secondary fault. F2-1 secondary fault is an active fault, its vertical activity rate has been 0.12mm/a since the Late Pleistocene. Activity of F2-2 secondary fault has been weak since the Late Pleistocene. Compared with the result of drilling exploration, the CSAMT method and shallow seismic reflection method have some advantages in exploration of bedrock interface, whereas the high density resistivity method is good at exploration of shallow loose deposits and can display more effectively broken point of fault. By means of comprehensive geophysical-drilling exploration, researchers can achieve the complementary advantages, and can reduce the uncertainty of the interpretation for buried active faults exploration.