Bifurcated Crustal Channel Flow and Seismogenic Structures of Intraplate Earthquakes in Western Yunnan, China as Revealed by Three‐Dimensional Magnetotelluric Imaging

Abstract

AbstractBased on broadband magnetotelluric data collected in western Yunnan, we obtain a three‐dimensional crustal resistivity model, which reveals seismogenic structures of Yingjiang and Longling earthquakes. Our model suggests a bifurcation of the crustal flow in western Yunnan, with a southwestern branch running into the Tengchong Block north of the Dayingjiang Fault and a southeastern branch flowing into the Baoshan Block. The Yingjiang region features an upper and midcrustal resistive body above 20‐km depth, surrounded by conductors in the midcrust. Six moderate earthquakes in Yingjiang occurred in the transition zone between the resistive and conductive structures. These earthquakes occurred in the context of a right‐lateral accommodation zone between the Nabang and Binglangjiang Faults and in the presence of the southwestern branch of the crustal flow, which provides a mechanical decoupling under the rigid high‐resistive upper crust. Beneath the Longling area, a high‐resistive structure extends through the entire crust, but a zone of low resistivity is embedded in the depth range of 10–25 km where the 1976 M7.3 earthquake occurred. The high‐resistive body provides a blockage to the previously proposed crustal channel flow along the Gaoligong shear zone and may accumulate sufficient stress. The Longling strong earthquakes may result from the sinistral strike‐slip motion of the Ruili‐Luxi Fault in the framework of the north to northeast trending compressive stress. The blockage to the crustal channel flow along the Gaoligong shear zone by the high‐resistivity zone in Longling could be an important factor to produce the north to northeast trending compressive stress field in Longling area.