Typical Riedel shear structures of the coseismic surface rupture zone produced by the 2021 Mw 7.3 Maduo earthquake, Qinghai, China, and the implications for seismic hazards in the block interior

Abstract

Large earthquakes in the Tibetan Plateau generally occur on block-boundary faults and produce coseismic surface ruptures that indicate the sense of block movement. However, seismic hazard in the block is less concerned. The Mw 7.3 Maduo earthquake on 22 May 2021 hit the internal Bayan Har block, which provides a rare opportunity to study the deformation features of the intra-block tectonics in central Tibet and related kinematics implications. We developed the high-resolution survey via the DJI drone of Phantom 4 Pro RTK and detailed field observations, to sum up the typical characteristics of the Maduo coseismic surface rupture zone. Then we classified these surface ruptures based on rupture orientation, spatial distribution, and stress state and analyzed their kinematic mechanisms. Our results indicate that (1) the typical surface ruptures of the Maduo earthquake are shear fractures, tensional cracks, and mole tracks, which follow the Riedel shear model; (2) the Riedel shear structures reveal a sinistral strike-slip movement sense for the seismogenic fault, accordant with regional tectonics; (3) seismic potential on minor faults in the interior block should be emphasized highly. This study will not provide insights into the kinematics of surface ruptures on a strike-slip fault but will strengthen the understanding of seismic hazards on an intra-block active fault.