Three Dimensional Geological Modeling And Analysis Of Seismotectonic Environment In Changning Area,South Sichuan

Since the 2008-5-12 Wenchuan M8.0 earthquake and 2013-4-20 Lushan M7.0 earthquake,the seismicity in South Sichuan tends to be active,especially in Changning area,where the 2019-6-17 Changning MS6.0 earthquake occurred.Based on the theory of structural geology,using the knowledge of neotectonics,seismogeology and related software,this paper analyzes the seismotectonic environment in Changning area of South Sichuan by combining the field visit and data collection after the earthquake,and further analyzes the different characteristics of each region of the seismotectonic environment in Changning area of South Sichuan,in order to have a better understanding of the earthquake prevention and disaster reduction in this area Help.Based on the field investigation,structural shape analysis,3D geological modeling,aftershock epicenter interpretation and other research methods,the seismic structural environment of South Sichuan is analyzed.The results are as follows:(1)the focal mechanism solution of 14 earthquakes in the study area and its surrounding areas and the tectonic stress direction of each earthquake are calculated.The number of tectonic stress earthquakes in the northwest southeast direction in the study area is more than that in the east-west direction There are many earthquakes in the direction of NE-SW.(2)The main stress direction of the modern tectonic stress field in the basin is the same as that of the modern tectonic stress field in the study area,i.e.from northwest to Southeast.(3)There are three different seismic tectonic environments in the study area,which together with Huayingshan fault form an irregular quadrilateral block.In the study area,11 moderate and strong earthquakes with MS ? 4.7 occurred in 3 seismic tectonic environments,and occurred in sequence from south to north.(4)Leyi anticline tiantaisi fault is the south boundary of the irregular block.The section of tiantaisi fault inclines to the north.Influenced by the main stress direction of the northwest southeast direction,the irregular quadrilateral block thrusts to the southeast.The earthquake in this structural part shows the characteristics of thrust or thrust strike slip.(5)The southeast wing of Yuhe anticline northwest wing of Jianwu syncline is the southeast boundary of the irregular block.The fold movement mode of the study area is fold before fault,that is,the rock layer is first pressed and folded,and the steep wing stratum is thinned due to the continuous action of the main stress in the Northwest southeast direction.After exceeding the elastic strength of the rock layer,the thrust fracture is developed in the fold and steep wing.The earthquakes in this area are characterized by thrust or thrust slip.(6)The central thrust fault in the northwest core of Changning anticline and a series of small faults distributed intermittently are the Northeast boundary of the irregular block.Due to the southeast thrust of the irregular block(footwall of the fault),the hanging wall of the fault presents the seismic activity of sinistral strike slip and some slight normal faults(such as the 2019-6-17 Changning MS6.0 earthquake).