Coseismic surface rupture and seismogenic structure of the 2022 Ms6. 9Menyuan earthquake, Qinghai Province, China
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    Abstract:

    At 01:45 Am on January 8, 2022, a relatively strong Ms 6.9 earthquake occurred in Menyuan County, Haibei Prefecture, Qinghai Province, China. The epicenter was located near the Lenglongling fault, which is the central western segment of the Haiyuan fault zone, northeastern Qinghai- Tibet Plateau. Field investigation from the day after the earthquake showed that it produced a series of co- seismic surface ruptures in the plateaus mountainous area at an altitude of 3500~4100 m, with tension cracks, tensional- shear cracks, shear cracks, mole tracks and sags. The main rupture strikes NWW—SEE and is characterized by left- lateral strike- slip motion over a total length of ~27 km. The rupture zone is divided into two main branches: the northern and the southern branches. The northern branch follows the Lenglongling fault segment of the central and western Haiyuan fault, while the southern branch is located 3 km southwest of the northern branchs western terminus, following the Tuolaishan fault, thus forming a left- step with the northern branch. Such trending variation and step characteristics suggest that the rupture zone can be divided into three segments: western, central, and eastern segments, consistent with the distribution of surface co- seismic displacements. The N93°E- striking, ~4.5 km- long western segment, i.e., the southern branch of the rupture zone, displays a maximum horizontal offset of ~85±10 cm. The N102°E- striking, ~7.5 km- long central segment, i.e., the western part of the northern branch, has a maximum horizontal offset of 3.7±0.1 m. The N110°~120° E- striking, ~15 km- long, eastern segment, i.e., the eastern part of the northern branch, exhibits a maximum horizontal offset of ~3.0±0.3 m. The fact that such rather small earthquake magnitude produced such long surface rupture and impressive surface deformation implies that the focal depth of 2022 Menyuan earthquake may be much shallower than 10 km. Seismogenic fault of the 2022 seismic event is the Lenglongling fault, forming a compression bend with flower structure along the Haiyuan fault system. The southeastward spreading direction of the aftershocks related to the 2022 Menyuan earthquake suggest an eastward stress migration. Therefore, seismic hazard along the Jinqianghe, Maomaoshan, and Laohushan faults in east of the Lenglongling fault, has dramatically increased because they are lying in the seismic gap between the 1920 Haiyuan earthquake and the 2022 Menyuan earthquake.

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Pan Jiawei, Li Haibing, Marie- Luce Chevalier, Liu Dongliang, Li Chao, Liu Fucai, Wu Qiong, Lu Haijian, Jiao Liqing.2022. Coseismic surface rupture and seismogenic structure of the 2022 Ms6. 9Menyuan earthquake, Qinghai Province, China[J]. Acta Geologica Sinica,96(1):215-231

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History
  • Received:February 17,2022
  • Revised:February 20,2022
  • Adopted:
  • Online: February 21,2022
  • Published: