The West Qinling orogenic belt is an important portion of the east-west trending orogenic system in mainland China. In order to study the east-west differences and tectonic setting of major earthquakes in this area, a magnetotelluric (MT) sounding (WQL-L1) has been carried out across the central part of this orogenic belt,named the Aba-Zoige-Lintan-Lanzhou profile. MT data were collected and two-dimensional inversion and interpretation were made to these data. Combining the MT results of WQL-L6 across the Minxian-Zhangxian earthquake zone in 2013 and geological and geophysical data available, we study the deep electrical structure, the major faults and their contact relationship with the north and south sides. The results show that the East Kunlun fault system is composed of the Diebu-Bailongjiang fault and Guanggaishan-Dieshan. This fault system is the boundary between the Songpan-Garze block and West Qinling orogenic belt. The West Qinling fault is a significant electrical boundary zone that extends through the Moho. The Lintan-Dangchang fault is also an electrical boundary, extending toward east and west in different manners. Along the central West Qinling orogenic belt the overall electrical structure presents a high-resistivity characteristic from the earth' s surface to a depth of about 20 km. It is shallow in northeast and southwest while deep in the middle, like a inverted "trapezoid". Under the high-resistivity layer of the West Qinling orogenic belt is low-resistivity layer. They coupled each other, showing a compression and accumulation style. The low-resistivity layer in the north of the Songpan-Garz'e block is deep in southwest and shallow in northeast, implying northeastward movement of the Tibetan plateau. The Longxi basin has a stable layered structure. The central West Qinling orogenic belt now is under the extrusion and squeezing from the Songpan-Garz'e block and Longxi basin. The seismic source of the Minxian-Zhangxian Ms6.6 earthquake is located in the core of inverted "trapezoid" of the low-resistivity layer of the central West Qinling orogenic belt, which is the contact between the upper crust high-resistivity layer and lower crust low-resistivity layer. It is also located near the Lintan-Dangchang fault that shows a low-resistivity zone cutting the crust. The Songpan-Garze block pushes from southwest to northeast and the Longxi basin block resists from northeast to southwest, which is the external dynamic mechanism of the Minxian-Zhangxian Ms6.6 earthquake, as well as the internal factor of material property. Such an environment of compression and its internal special structure might have caused the crust of the central West Qinling to be shortened in the horizontal direction and to rotate clockwise as well as to uplift strongly. The inverted "trapezoid" body of the central West Qinling orogenic is buried shallow in the west and deep in the east, which may be related with less and more historical seismicity in western and eastern sections of the Lintan-Dangchang fault, respectively. This system accommodates the slip rates of the east-trending Kunlun fault, which may be the deep reason why the strike slip rate along the East Kunlun fault reduces from west to east.
