Investigation And Study On The Late Quaternary Activity Of Maodong Fault Zone In The Central Part Of Southern Jiangsu Province

The M5.5 and M6.0 earthquakes in Liyang in 1974 and 1976 are closely related to the Maodong fault.In southern Jiangsu,there are many highways,high-speed railway lines,oil and natural gas pipelines.The Beijing-Shanghai High-speed Railway,the Nanjing-Hangzhou High-speed Railway,the planned Zhenjiang High-speed Railway,and the intercity along the river in southern Jiangsu all Lence the Maodong fault zone.The systematic investigation of fault activity and activity rate in the crossing area is of great practical significance for the later engineering construction.For Mao east fault zone in the middle of bedrock exposed area,carriedout a serie s of forefathers'research,but maodong fault zone is a piecewisemostly covered with loose bed,fault location in loose bed cover areasexual characteristics,relatively,the north east and south west extension ís compared to the bedrock outcropped area are difficult to determine,thespatial distribution characteristics and the extension of the north east tokwun tong-fracture following fracture and Ru Shan-will take is st ill notclear,for loose bed coverage area of the lack of system study of shallowseismic exploration and drilling joint section.By collecting the previous data and using the geophysical exploration method,this paper makes a comprehensive analysis of the Maodong fault.It accurately defines the spatial position and spatial distribution characteristics of the fault through the shallow seismic reflection wave method.And it sets up four borehole exploration lines along the seismic wave exploration line to obtain the quaternary stratigraphic characteristics.The geometric and kinematic characteristics of the Maodong fault are analyzed by comparing stratigraphic sequence in southern Jiangsu and combining borehole profile,and the dynamic background of the Maodong fault is obtained at the same time.This paper mainly made the following points:(1)Geophysical exploration shows that the main fault of Maodong fault zone has a tendency of E,but the secondary fault with a tendency of W is Y "broom" in space.The fault property belongs to reverse fault,which occurs in the bedrock,and no fault upper break point is found in the upper overburden.(2)The borehole joint section shows that the overburden strata has good continuity and no stratigraphic dislocation.Compared to the standard strata in southern Jiangsu,covering layer can be divided into one cycle in the Holocene Rudong Group(Qhr)and two cycles in the Late Pleistocene Lake Group(Qp3g).The formation lithology is consistent with the standard formation.It indicates that Maodong fault has no activity or weak activity in the holocene.(3)The above study shows that the Maodong fault zone is distributed along NNE direction as a whole,which has the property of sinistral shear and thrust nappe,and the activity intensity and movement mode of each section are inconsistent;the time is characterized by periodicity,and the movement time of each section is also inconsistent,but its activity time is mainly concentrated in late Pleistocene.