Complex structural fault system and distributed deformation across the Big Bend of the Red River fault, Yunnan, China

• Published in: Physics of the earth and planetary interiors Vol. 333; p. 106942
• Main Authors: Wen, Xueze, Ma, Shengli, Fang, Lihua, Liang, Mingjian, Du, Fang, Long, Feng, Zhao, Xiaoyan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2022
• Subjects: Distributed deformation partitioning; Fault zone architecture; Prehistoric rupture; Red River fault; Restraining bend segment (Big Bend); Seismogenic capability; Prehistoric rupture; Distributed deformation partitioning; Restraining bend segment (Big Bend); Fault zone architecture; Red River fault; Seismogenic capability
• ISSN: 0031-9201; 1872-7395
• DOI: 10.1016/j.pepi.2022.106942

To understand why the 130 km-long restraining bend segment (Big Bend) of the Red River fault (RRF) in Yunnan lacks historical ruptures and has a low geologic slip-rate, deep seismic profiles, relocated earthquakes and GPS-measured velocities are integrated to investigate the fault zone architecture and deformation associated with this segment. The Middle to Late Cenozoic southward extrusion of the Chuan-Dian Fragment, along with the northeastward blocking of the Yunxian Convex, have curved the RRF and its sub-parallel faults towards the southwest, forming the Big Bend. Branch faults split off the Big Bend RRF at depths between the upper lithosphere-mantle and the lower middle crust; splaying upward and sideward, they either connect/reactivate preexisting faults or become blind faults in the middle to upper crust, resulting in seismically active Lancang, Blind Wuliangshan, Qujiang and similar faults on both sides of the Big Bend. Together these faults form a complex fault system that shows a trans-crustal flower structure with a ∼ 350 km width at the surface. Across this fault system GPS-measured dextral-shearing at ∼8 mm/a and horizontal-shortening at ∼3.5 mm/a represent the deep deformation rate of the Big Bend RRF under the flower structure. 85% ± of the deep shearing and almost all of the deep shortening are partitioned onto branch and subsidiary faults bounding and within the flower structure, and only 15% ± of the deep shearing to the Big Bend RRF in the brittle crust, due to the complex fault system architecture and the existence of a large-scale asperity on the main RRF in the brittle crust. Across this fault system the deformation partitioning mode is nearly distributed. Active faulting and prehistoric surface rupture suggest that the Big Bend RRF has the capability to produce large earthquakes at recurrence intervals of millenniums, much longer than the local written earthquake history of 300–500 years. [Display omitted] •The Red River fault (RRF) Big Bend and its sub-parallel faults form a late-Cenozoic reactivated fault system.•This fault system is an ∼350 km-wide trans-crustal flower structure with distributed deformation.•With 85% ± of the deep RRF deformation, branch faults of the flower structure are the main seismogenic structures.•With 15% ± of the deep shearing, the main Big Bend RRF in the brittle crust has the capacity to produce large earthquakes.•Large earthquakes on the Big Bend RRF likely recur at the interval of millennial, much longer than local history.