Magnetotelluric Profiles The Electrical Conductivity Structure Of Minjiang-Huya Fault Zone

This paper is based on the "Deep Seismic Reflection Profiling Experiment and crustal structure research" projects under the thematic "Minjiang fault sectional magnetotelluric survey and lithospheric electrical structure research". In the whole process,I participated in the field data acquisition and date editing and processing. I eventually got the study area of magnetotelluric sounding data of impedance. In the study area we established three electromagnetism profiles. By the impedance tensor decomposition method, we speculated electrical axis direction of the measuring point. By combining with geophusical research and geological speculated, we got the electrical spindle direction of each profile. The results of calculation of skewness show that the most of the study of the area is 2‐D characteristic, deep partial area showing the 3‐D characteristics. Nonlinear conjugate gradient method(NLCG) is adopted in this paper. 2‐D inversion calculation of the data in the study area was carried out. Through different modes, different parameter settings inversion, the best inversion model is obtained by comparing the different inversion results. According to the geophysical anomaly and fault mainly in the geoelectric model, we inferred from the study area eleven major fault: Longriba fault zone, Minjiang fault zone, Huya fault as well as many secondary faults. And fault location is consistent with geological data location.From the inversion results we can see that, the Minjiang fault zone crustal substantially are resistive bodies and hickness of between 20km‐30km. Low resistivity and high conductivity layer is in the middle and lower crust and communicates with the district Minshan, Minjiang River and longriba deep fault zone. The east side of the Minjiang fault, 40 km depth is a large block of high block. Huya fault along the profile of upper crust is of high resistivity,between 20 km and 30 km. Low resistivity and high conductivity layer in the middle lower crust, communicates with the district eye teeth deep faults and secondary faults. On the east side of The Huya fault, the depth of 30 km under the large‐scale is high resistance block.The side shallow resistive bodies of Minjiang fault and the east side of the deep resistive bodies of Huya fault, is likely Yangtze craton, We can get the contact relationship between the Yangtze block and the crust of the Qinghai Tibet. Through inversion model and geological data we can be drawn that the western boundary of the Yangtze plate has crossed the Longmen mountain fault zone and extended to the nearby Longriba fault. So Minjiang fault is likely to be the eastern boundary of the Tibetan Plateau. In the inversion results, in the lower crust appears high conductivity low layer, in addition, the low speed and high permeability layer seems to have a tendency to expand outward. It is likely to be the result of the interaction between the subsurface fluid and partial melting.