Late Quaternary Tectonic Deformation of the Xinminpu Fault and Mechanism of 1785 Huihuibao Earthquake Based on Unmanned Aerial Images

Yu Jinchao; Li Shuwu; Yuan Daoyang; Wang Youlin; Wen Yameng; Zhang Lijun; Chen Luyao

doi:10.3799/dqkx.2024.077

Abstract：The Xinminpu fault is the northernmost reverse fault-fold belt in the Jiuxi Basin which is at the western of Hexi Corridor,still active in the Late Holocene and its offset geomorphology is clear.In this paper,cumulative offset of Xinminpu fault and co-seismic surface offset of the 1785 Huihuibao Earthquake are determined from tectonic geomorphology by high-precision unmanned aerial vehicle SfM photogrammetry and fine interpretation of offset geomorphology.Based on high-resolution topographic and geomorphologic data,a total of 90 groups of fault scarp offset were measured and counted,and combined with cumulative offset probability distribution plot,seven offset clusters were obtained,and it is inferred that about seven paleoseismic events occurred in Late Quaternary of Xinminpu fault,with quasi-periodic recurrence characteristics,and that the latest two peak offset of 0.9 and 1.5 m corresponded to the earthquake in 1785 and a paleoseismic event at 3.8±0.3 ka ago,respectively.Based on average coseismic offset of 0.9 m,the magnitude of the 1785 Huihuibao earthquake is about M6.6,which is consistent with historical seismic results.Combined with the listric fault model,the vertical slip rate of Xinminpu fault since Holocene was determined as 0.1±0.02 mm/a,and the horizontal shortening rate was about 0.18±0.06 mm/a.Comprehensive analysis shows that the 1785 Huihuibao earthquake was an inverse fault-fold type earthquake on Xinminpu fault,which is similar to the seismogenic mechanism of the 2003 Ms6.1,Ms5.8 Minle-Shandan earthquake in Gansu Province and the 2002 Yumen Ms5.9 earthquake that occurred in the central of the Hexi Corridor,indicating that it has a reverse fault-folding type seismic mechanism in the basin of Hexi Corridor,and further research and seismic defense for this type of seismic tectonic belts should be strengthened in the future.