16:15 〜 16:30
[MIS04-14] Seismo-tectonics of strong earthquakes based on magnetotelluric data in western Yunnan
Based on broadband magnetotelluric (MT) array data, we have obtained the three-dimensional (3-D) electrical resistivity model in western Yunnan, the southeastern Tibetan Plateau where the seismic activities occur. Our MT model reveals the seismogenic structures of earthquakes in western Yunnan. The seismogenic faults in the Gaoligong Shear Zone (GLGSZ) are characterized by subvertical conductive zones bounded by resistive upper crustal layer on both sides. Moderate earthquakes near the GLGSZ have all occurred within the conductive fault zones at the bottom of the upper resistive crust. Our model also 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, surrounded by conductors in the midcrust. Moderate earthquakes in Yingjiang also occurred in the transition zone between the resistive and conductive structures, in the context of a right-lateral accommodation zone and in the presence of the southwestern branch of the crustal flow, which provides a mechanical decoupling under the rigid high-resistive upper crust. In the Longling area, a high-resistive structure extends through the entire crust, but a zone of low resistivity is embedded. 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.