Preliminary study on active features of Fenghuang-shan-Tianshui fault, West Qinling north boundary fault zone since the late of Late Pleistocene

摘要

West Qinling north boundary fault zone (WQNBFZ) is a major NWW-striking fault in the east boundary of Tibetan Plateau, which is parallel to the Xianshuihe fault zone, Eastern Kunlun fault zone and Haiyuan fault zone. It is of mainly sinistral strike-slip. England and Molnar (1990) and WANG and MA (1998) proposed that these strike-slip faults divided the east part of Tibetan Plateau into elongate blocks, which slide successively towards the east, accompanied possibly by the clockwise rotation. What is more, the occurrence frequency of earthquakes with M 36.5 along WQNBFZ is also high, such as BC 47 Zhangxian M=6.8 earthquake, the 128 Gangu M=6.5 earth-quake, the 143 Gangu M=7 earthquake, the 734 Tianshui M=7 earthquake, the 1756 Wushan M=6.5 earthquake and the 1936 Kangle M=6.8 earthquake. However, compared with researches on Haiyuan fault zone, Xianshuihe fault zone and Longmenshan fault zone (Institute of Geology of State Seismological Bureau, Seismological Bureau of Ningxia Hui Autonomous Region, 1990; LI, 1993; DENG, et al, 1994; Burchfiel, et al, 1995), the study on WQNBFZ is still weak, although some researches have been done by KANG (1990) and TENG, et al (1991). Based on the field investigation and sample dating, the active features about the Fenghuangshan-Tianshui fault (FTF) of WQNBFZ are discussed in the paper.……