Study On The Electrical Structure Of Crust-mantle In The Western Sichuan Plateau And Sichuan Basin

The western Sichuan Plateau is located on the eastern edge of the Qinghai-Tibet Plateau,where seismic activity and tectonic movement are active.In order to study the seismogenic mechanism of earthquakes in the region and the dynamic mechanism of the crustal uplift and thickening in the western Sichuan Plateau,the lithospheric electrical structure model should be determined first.This paper relies on 52 broadband high-frequency magnetotelluric sounding points obtained from the "Tibet-Western Sichuan 3D lithospheric electrical structure survey project",systematically comprehensive analysis of its data,refined data processing,and impedance tensor GB decomposition technology.Phase tensor analysis The dimensional and electrical principal axis analysis of the magnetotelluric sounding impedance tensor data in the study area shows that the main electrical structure of the middle and upper crust in the study area is a good two-dimensional characteristic,relatively deep Three-dimensionality.The best two-dimensional inversion model is obtained by comparing the two-dimensional inversion models with different parameters and modes.The three-dimensional electrical model of the middle and south sections of the Longmenshan tectonic belt is obtained by using the ModEM three-dimensional inversion technique based on the NLCG inversion algorithm.The geological problems such as the lithospheric structure and dynamic mechanism of the Longmenshan area provide electrical basic data.Combined with the electrical structural model and other geological and geophysical data,the cause of the earthquake in the Longmenshan fault zone is the “T”-shaped structure formed by the high-conductivity layer in the Songpan-Ganzi shell and the high-resistance body in the Longmenshan,which makes the seismic stress accumulation easy.Triggered an earthquake.The Hersau flow model can be used to explain the crustal uplift and thickening of the western Sichuan Plateau.The crustal flow controls the distribution of earthquakes and affects the focal mechanism of the earthquake.Most of the seismic depths in the western Sichuan Plateau are in the upper crust,on the side of the electrical gradient zone close to the high-resistance body.Conducive to the earthquake.