The Research On The Relation Between Electrical Structure And Earthquake In West Qinling Mountains And Its Adjacent Areas

The West Qinling belt is located in intersection area between the North-South seismic belt and the northeastern margin of the Qinghai-Tibet Plateau.The historical earthquakes are frequent in the area.The research for the deep structure of the area is of great significance for the dynamic evolution of the correlative block.Meanwhile,it helps to understand and solve regional geological problems,basic geological science problems and the correlative earthquake problems.In this paper,we use the magnetotelluric data based on the "Sinprobe" and the "magnetotellurics array observation of the intersection area of central orogenic belt and the North-South seismic belt Intersection" to explore the relationship between deep electrical structure and earthquake in the West Qinling belt and adjacent areas.Firstly,we got the high Signal-Noise ratio MT data by using data processing methods such as reference and power spectrum selection.Data analysis adopt methods such as phase tensor analysis,impedance tensor decomposition,and magnetic induction vector analysis.The results show that the crust and the deep part are mainly two-dimensional structure,and there is three-dimensional effect.The polarization phenomenon is strong and there is not polarization direction in the West Qinling block and Songpan-Ganzi block.The deep geological structure are complex.The tectonic trend direction of the middle-lower crust of the West Qinling block and the Qilian block is the obvious northwest direction,and the construction direction of the Songpan-Ganzi block and the Sichuan basin is northeast direction.Secondly,we got a relatively reliable electrical structure model by the 2D/3D inversion.The results show that the electrical structure has certain differences in different blocks,and the block and layer features are obvious.The electrical structure of the Qilian block is dominated by high resistance,and high conductors is found in the crust,so the block is relatively stable.The electrical vertical delamination of the West Qinling block is obvious,and the electrical structure is characterized by high-low-high resistance stratification,and large-scale high-conductivity layer exists in the upper-middle crust.The electrical structure of the Songpan-Ganzi block is more complicated,but the deep electrical structure of the Sichuan Basin is simple,with a low-high-low resistance three-layer layered structure.It is inferred that the high conductors of the crust in the West Qinling block and the Songpan-Ganzi block are the result of the combined effects of partial melting and salt-bearing fluids,which may be the channel for the eastward movement of the Qinghai-Tibet Plateau.Finally,combining with earthquake data,we discusse the relationship between deep electrical structure and crustal deformation,earthquake,and analyse the seismogenic environment of middle-strong earthquakes and stability of the block in the West Qinling belt and its adjacent areas.The results believe that strong crustal deformation occurred in the West Qinling and Songpanganzi blocks due to the compression-blocking effect,and there are closely relationship between the earthquake and the electrical structure.The areas where the medium-strong earthquakes occur usually have the same electrical features: located in areas with strong crustal deformation;electrical structures are complex,and high resistivity bodies have a certain large scale,and the high and low resistance are juxtaposed,and there is clear obvious boundary lines;and there are corresponding faults or energy release channels.Based on these,it is believed that there are instability and the earthquake is frequent in the Longmenshan fault,west Qinling and the Songpan-Ganzi block,while the Qilian block is relatively stable.