A magnetotelluric study of 3D electrical resistivity structure underneath the southern segment of the Red River fault zone, South China

Abstract

• Imaged 3D resistivity structure beneath the southern Red River (RRF) and Xiaojiang Faults (XJF). • The southern RRF was shown electrically resistive and proposed mechanically strong. • The XJF shows a subvertical fault conductor zone under its eastern branch fault. • The southern RRF may have no large earthquakes in the future based on our results. The Red River Fault (RRF) is a continental-scale strike-slip fault forming the southwestern boundary of the Chuan-Dian block in the southeastern Tibetan Plateau. The kinematics and seismicity along the RRF are under debate over the years. Here, based on broadband magnetotelluric array data, we present a fine 3D electrical resistivity model in the southern segment of the RRF and its adjacent Xiaojiang fault zone (XJFZ). Our MT model shows a prominent electrical resistor extending to a depth of ∼20 km beneath the RRF and Ailao Shan shear zone. The southern RRF is imaged as a resistive fault zone, indicating no crustal fluids within this fault. The XJFZ represents a sub-vertical fault conductor zone bounded by bilateral crustal resistive blocks but a sharp contrast of resistivity across its western branch. The fault conductor zone along the eastern branch of the XJFZ ends at the resistive RRF, indicating the XJFZ may not develop beyond the RRF southward. Our MT model indicates that the resistive southern RRF is possibly not capable of occurring large seismicity in the future, but the southern end of the XJFZ is with seismic risk potential.