关键词: 幕府山-焦山断裂, 第四纪活动性, 浅层地震勘探, 钻孔联合剖面

Abstract: Abstract: Running across the Zhenjiang and Nanjing area, The Mufushan-Jiaoshan Fault is an important near EW- trending faults in Nanjing and Zhenjiang area. It extends from Mufu Mountain through Yanziji, Qixia Mountain, and Longtan to Jiao Mountain of Zhenjiang, with a total length of about 75km. The overall trend of the Mufushan-Jiaoshan Fault is nearly east-west, dipping to the north, the southern side of the fault is Ningzhen mountain, the north side is the hollow land along the river and the Yangzhou low hilly plain. There have been many destructive earthquakes in the Nanjing-Zhenjiang area, most of which occurred at the intersection of NW trending faults and near EW Mufushan-Jiaoshan Fault. It is of great significance to study the nature, characteristics and the latest active times of the Mufushan-Jiaoshan Faults for the prevention and reduction of earthquake disaster in Zhenjiang city and Nanjing city. Previous work mainly focused on the Nanjing section, and judged that its latest activity age is late Middle Pleistocene; there has not been a systematic study on the fault in the Zhenjiang section, and its latest activity age is still unclear. Based on the project of "Urban active fault exploration and seismic risk assessment in Zhenjiang City", we have carried out a series of shallow seismic exploration work for Mufushan-Jiaoshan Faults in the Zhenjiang section, and selected representative points to carry out drilling joint profiling method, and studied the Quaternary activity characteristics of the Mufushan-Jiaoshan faults. The results are of great significance for urban earthquake disaster reduction, urban planning and land use. The results of shallow seismic exploration show that the Zhengjiang section of the Mufushan-Jiaoshan Fault is dominated by normal faulting,and the trend is NEE, dipping to the north, with a dip angle of about 50°~60° and a displacement of 3~7 m on the bedrock surface. All breakpoints of Mufushan-Jiaoshan fault show that only the bedrock surface was dislocated, not the interior stratum of Quaternary. On the Qiaotou village site, there is no sign of dislocation in the stratum above the Middle Pleistocene, The lower part of Middle Pleistocene Xiashu formation has been dislocated, The displacement of the bottom boundary of the Middle Pleistocene on both sides of the fault is 3.2m. According to the characteristics of dislocated stratum, the latest active age of Mufushan-Jiaoshan fault is late Middle Pleistocene, There is no evidence of activity since late Pleistocene. The activity of the north branch fault is dominated by normal fault on the Jinshan site, and there is no evidence of faulting in the Holocene. Based on the comprehensive analysis, the latest active age of the Zhenjiang section of the Mufushan-Jiaoshan fault is the late Middle Pleistocene, and there is no evidence of activity since the late Pleistocene. According to the dating results, the latest activity time is after 222 ± 22 Ka and before the late Pleistocene. Mufushan-Jiaoshan fault is a major fault with strong seismic risk in Ningzhen area, especially at the intersection of the fault and the NW trending fault, which has the seismogenic environment of destructive earthquake. It is necessary to attach great importance to the prevention of earthquake damage in the relevant area.

Key words: Mufushan-Jiaoshan fault, Quaternary activities, Shallow seismic exploration, Drilling joint profiling