Abstract:
At 01:45 on January 8, 2022, a
MS6.9 earthquake occurred in Menyuan County, Haibei Tibetan Autonomous Prefecture, Qinghai Province. The epicenter was located at (37.77°N, 101.26°E) in Lenglongling area of the central Qilian mountains, with a focal depth of 10 km. According to the comprehensive results of field investigation and aerial image interpretation by unmanned aerial vehicle (UAV), the seismogenic fault of this earthquake undertakes a sinistral strike-slip motion, with a slight thrust component, the surface rupture zone of this earthquake is composed of the north main rupture zone located at the west end of Lenglongling fault and the southwest secondary traction rupture zone located at the east end of Tuolaishan fault. A series of tension step-overs, sinistral displacements, tensile fractures, compression bulges, and compression ridges were formed along the earthquake rupture zone, resulting in damage to the Lanzhou-Xinjiang high-speed Railway tunnels and bridges and the suspension of train services. In order to comprehensively analyze the different types of surface fracture features and seismic damage caused by this earthquake, field investigations and aerial interpretation using UAV were conducted along the rupture zone. As a result, typical co-seismic surface fracture features along the rupture zone were categorized as follows: ① Various typical geometric structures, including echelon secondary rupture, sinistral pull-apart step-overs, sinistral compression step-overs, dendritic and netlike forked rupture,
etc; ② Horizontal displacement observed in various geomorphic markers, such as left-handed fences in pastoral areas, truck trace, animal footprints, and gullies and gully ice; ③ Various types of vertical rupture, such as thrust seismic scarps and normal seismic scarps; ④ Various types of compression rupture, such as compression ridges and compression bulges; ⑤ Different types of tensile fracture zones, including pure tensile fractures and tensile-shear fractures. The geological and engineering seismic damage caused by the earthquake can be summarized as follows: ① Slope instability across the earthquake fault zone; ② Damage to highways, bridges, and tunnels across the earthquake fault zone; ③ Seismic deformation such as ice bulges and highway cracks in the areas near the earthquake fault zone. In addition, with the analysis and discussion on the distribution characteristics and formation mechanisms of the aforementioned phenomena, it should be emphasized the importance of strengthening engineering anti-rupture fortification when crossing active faults and nearby seismic fortification of strong ground motion zones.