A Research On Three-Dimensional Electrical Structure And Geodynamics In Northeast Yunnan

Northeast Yunnan is located in the southeastern margin of the Qinghai-Tibet Plateau,at the boundary of different structural divisions.A variety of faults have developed in northeastern Yunnan,among which some sections of Zhaotong-Ludian fault and Xiaojiang fault can accumulate high stress and have strong seismogenic potential.Based on the regional magnetotelluric array observation data collected in Qiaojia,Dongchuan,Ludian and other regions,this paper obtained horizontal and vertical slices of three-dimensional electrical structures using three-dimensional magnetotelluric inversion,which completely reveals the deep electrical structure in northeastern Yunnan.The distribution characteristics of high resistance layer and low resistance layer basically correspond to the tectonic background of this area.The inversion result shows that Zhaotong-Ludian fault has developed several local high resistance bodies within10 km depth.The southwest side of the Qiaojia-Dongchuan section and the intersection of the east section of Xiaojiang fault all show high resistance in upper crust.These regions all show stronger seismogenic ability.This paper discusses the seismogenic mechanism of the northern segment of Xiaojiang He fault zone in Ludian earthquake area.It is speculated that the frequent seismic activity in Ludian source area may be related to the development of active faults,the lithologic differences of rocks at different depths,and the flow of low-resistivity thermal substances in the deep.The earthquake induced by Xiaojiang fault zone is related to its own shear movement and high resistance rock shielding.This paper combines surface heat flow,effective elastic thickness of the lithosphere,earthquakes and the electrical structure for analysis.It is speculated that the deep low-resistivity layer in northeastern Yunnan may be the lower crust channel flow whose plastic flow provides the deep power source for earthquakes in Ludian.