Electrical Property of Deep Structure in Songpan-Aba District

The magnetotelluric sounding (MT) surveying was recently conducted in the Songpan-Aba district in the northwest of Sichuan, a "delta" specific to the eastern part of the Tibetan plateau. The analysis of the two crossed MT inversion sections reveals a relatively stable block in the middle and deep structures of the Songpan-Aba district with conspicuous layers and few changes in electrical property. A low-resistivity layer about 10-20 km deep was found inside the crust. The electrical property of the deep layer (inside the mantle of the lithosphere) is classified as two types: the high-resistivity anomaly zone and the sub-high-resistivity anomaly zone with the low-resistivity layer inside the mantle. The corresponding lithosphere is about 120 km, so that the deep faults of the district contact their adjacent zones in all directions. The value of resistivity below the crust and upper mantle of the lithosphere is lower than that in its adjacent zones. The electrical property of the deep layer in this district is different from that in the uplifted Longmen Mountain, and also from that in the West Qinling structural zone characterized by both the high-resistivity basement and the thicker or thinner lithosphere.