Crust Density Inversion And Tectonic Characteristics Of Badong-Zigui Area

With the rapid development of the national economy and science and technology,the understanding of the underground structure has become an important research hotspot in the field of geosciences.Geophysical data is a comprehensive response of all underground materials.Through refined processing and separation,inverse research on specific geophysical properties of the ground can be performed.In this paper,we first study the basic theory of 3D inversion based on Lagrange multiplier constraints,discretize the underground space into a series of grid cells,and form an inversion objective function by constructing a model objective function and a data fitting difference function;Then the Lagrange multiplier is added to the inversion objective function to constrain it.In the inversion process,regional geological and geophysical data and other a priori information are added to make the constraint,so as to reduce the multi-solution and inversion of the inversion results.Uniqueness.On the basis of the above theory,the upright cuboid model and the complex model block are established,and the important parameters such as the depth weighting function,directional smoothing factor,Lagrange multiplier,and penalty factor in the theory are debugged and analyzed.The model basis of gravity and magnetic inversion carried out in the region.The Badong-Zigui Basin is located in the west of the Three Gorges region,with the Xuefeng Mountain thick-skinned structure belt on the south,the Qinling orogenic belt on the north,the Huangling anticline in the east,and the eastward extension of the Sichuan basin in the west.In the syncline structure,the sediments in the basin are mainly Late Triassic-Late Jurassic sandy muddy rocks,and the special tectonic environment has caused strong tectonic activities in the basin.Since the impoundment of the Three Gorges,earthquake events have occurred frequently,and most of them have appeared as small earthquake swarms;according to records,two destructive earthquakes occurred in the front line of Zigui,Badong,with a 5.1 earthquake in Zigui,Yichang in 1979 and Badong in 2013 An earthquake of magnitude 5.1 occurred in the county;on the southeastern side of the epicenter of the magnitude 5.1 earthquake in Badong,earthquakes of magnitude 4.3 and 4.1 occurred successively on June 16 and 18,2017.Seismic activity occurred frequently with the special geological structure background of the region and the Three Gorges reservoir Penetration is closely related.Using the three-dimensional gravity inversion,the underground three-dimensional density structure of the Badong-Zigui line and its adjacent area is obtained.The results show that the Zigui Basin is a low-density area from the periphery,the sediment thickness in the east is deeper than in the west,and the sediment density is smaller than in the west.The small and medium earthquakes in the area are basically concentrated 4-12 km underground,and the sedimentary activity is strong;At the same time,it is squeezed by the eastward extension of the Sichuan Basin,and it is speculated that there is a tendency of east-west movement and squeeze in the basin.