Study On The Activity Characteristics Of Neotectonic Period In Jiujiang Section Of Jiujiang-Jingan Fault

The Jiujiang area of Jiangxi is located at the junction of the three major tectonic units of the Yangtze plate,the Qinling-Dabie orogenic belt,and the South China orogenic belt.The junction of the NE-trending Tanlu fault zone,the Ganjiang fault zone and the northwest-oriented Xiangfan-Guangji fault zone,the geological structure is complicated.Earthquakes occur mostly at the intersection of faults,so it is necessary to study the fault activity in Jiujiang area.In this paper,the Jiujiang section of the JiujiangJing'an fault is taken as the research object.Based on the collection and summary of the previous achievements,the detailed remote sensing interpretation and surface survey and research of the Jiujiang section of the fault zone are carried out.Field geological surveys have determined that the Late Cenozoic strata in this area mainly include: Dagu Formation,Jinxian Formation,Yejialong red clay,Xingang clay,Lianyu Formation,and Poyang Lake Formation.The geochronological characteristics of the Jiujiang section of the Jiujiang-Jing'an fault were obtained by using the methods of remote sensing,drilling,geophysical exploration and structural joint analysis.(1)Remote sensing results show that the Jiujiang section of the fault zone indicates a clear surface structure,and the Quaternary gully geomorphology is distributed along the fault near the Lianhua Town.(2)The Quaternary combined borehole profile across the fault further preliminarily defines the possible fault distance of the fault in the Quaternary strata of different ages of 31 m,and the average slip rate during the Quaternary period is calculated to be 0.02 mm/year.(3)The geophysical profile of the combined activity of AMT and MT method shows that the fault location is in good agreement with the surface survey results,and reveals that the deep extension of the fault is very good.(4)Through the surface statistics of the conjugate shear joints in the Quaternary strata,it is concluded that the direction of the modern stress field in the area is mainly northeast and eastward,which is basically consistent with the tectonic stress field shown by the focal mechanism solution,indicating the current structure.The stress field and the tectonic stress field in the new tectonic period have obvious inheritance.(5)Preliminary kinetic analysis shows that the area is affected by the squeezing force of the Philippine plate,the northwest direction of the Pacific plate and the northeast direction of the Indian Ocean plate.The stress field of the modern northeastnear east-west extrusion is formed.Under this tectonic stress field,the NE-trending fault is more likely to slip and cause strong earthquake activity.Therefore,the JiujiangJing'an fault zone is the Quaternary active fault zone that should be the focus of future seismic risk assessment in the area.