Study On The Ground Motion Characteristics Of The Mogao Grottoes In Dunhuang

The Mogao Grottoes in Dunhuang is a precious cultural,historical,artistic,and scientific treasure left by history to mankind.It is located on the northeast edge of the Tibetan Plateau,adjacent to the Altun and Qilian Mountains,characterized by complex geological structures,intense tectonic activity,and frequent earthquakes.Throughout history,the grottoes have been affected by numerous seismic activities,causing varying degrees of damage to the cultural relics and murals within them.Given the unpredictability and destructive nature of seismic activity,carrying out preventive protection research on the Mogao Grottoes is particularly important.This paper is based on an extensive review of literature related to the Mogao Grottoes,and employs UAV photogrammetry to obtain high-precision DEM data of the Danghe Reservoir fault,located near the grottoes.The study analyzes the activity characteristics of the fault since the late Quaternary.Additionally,the paper collects data from the Mogao Grottoes Seismic Monitoring System and analyzes its strong-motion records to obtain the local seismic site effects.A simple model of the typical section of the Mogao Grottoes is established,and the ground motion load is input to carry out numerical simulation calculation,analyzing its displacement response distribution characteristics under different ground motion conditions.The following main conclusions are drawn:(1)The paper measures the vertical dislocation quantity of fault steep using MCSST and obtains the vertical dislocation quantity of different fault positions.Through comparative analysis,it is found that the maximum vertical dislocation of the fault scarp appears on the west side of the fault.Along the strike of the fault,the number of vertical dislocations is generally higher in the west and lower in the east,indicating that the activity of the west side of the fault is higher than that of the east side.(2)On June 16,2021,an M 5.8 earthquake occurred in Mangya,Qinghai Province.The seismic time-history of this earthquake was obtained by four strong ground motion stations in the Mogao Grottoes Seismic Monitoring System.The results showed that the maximum peak of the acceleration response was distributed in the short period,and the natural period was around T=0.5 s.The local site conditions of each station were the main factor causing the difference in acceleration response,with the site amplification effect of soil site>grotto site>rock site.In the east-west direction,the amplification effect of the thick soil site was obvious;in the north-south direction,the amplification effect of the grotto was relatively obvious;in the vertical direction,the amplification effect of various sites is basically consistent.Within the grotto,the greater the height,the more obvious the amplification effect of ground motion.(3)The numerical simulation results show that: in the future,the maximum displacement that the Mogao Grottoes can generate under the seismic load of basic intensity is about 0.9-1.57 cm.When the relative height of the cliff increases,the displacement also increases,and the displacement of the upper grotto is greater than that of the lower grotto.When the height is the same,the displacement of the corresponding point near the free boundary cliff surface is greater.The displacement results generated under different ground motion conditions are different.The larger the peak acceleration of ground motion,the longer the characteristic period,and the longer the earthquake duration,the greater the displacement results.Among them,the impact of the peak acceleration is the most significant,followed by the characteristic period,and the impact of ground motion duration is the smallest.The impact effect is more significant in locations with larger displacement responses.