Electrical structure of the Kunlun–Qinling fault system, northeastern Tibetan Plateau, inferred from 3-D inversion of magnetotelluric data

Abstract

Located in the northeastern Tibetan Plateau, the East Kunlun fault is a west–east left-lateral strike-slip fault that branches out into a horsetail-shaped structure known as the Kunlun–Qinling Fault system (KQFS) at its eastern terminus. The 2017 Jiuzhaigou Ms 7.0 earthquake occurred in this horsetail-shaped structure. The electrical structures of four profiles that cross different sections of the KQFS and Jiuzhaigou earthquake region are obtained in this study. Our results reveal key differences among these sections. The East Kunlun fault is the only electrical boundary in the Maqu section, whereas the Tazang, Bailongjiang, and Guanggaishan–Dieshan faults in the Tazang section form an imbricate fan structure that extends from south to north and merges into a high conductivity layer (HCL) in the mid–lower crust. Alternating high and low resistivity bodies below the KQFS revealed by the magnetotelluric method (MT) may be related to the cause of slip rate segmentation from the East Kunlun fault into the KQFS. The hypocenter of the 2017 Ms 7.0 Jiuzhaigou earthquake lies between the high and low resistivity bodies at the northeastern, shallowing edge of the HCL. The northern section of the Huya fault corresponds to a deep crustal electrical boundary. The Huya and Tazang faults form a one-sided imbricate fan structure that merges at depth into the HCL. The HCL is deep in the southwestern part of our study area but shallows to the northeast. This observation suggests that northeast movement of the Tibetan Plateau causes tectonic uplift and the frequent occurrence of strong earthquakes in this region.