Study On The Correlation Between Ground Motion Characteristics And Earthquake Damage In The Loess Area Of Min-Zhang Earthquake

The Minxian-Zhangxian Ms6.6 earthquake on July 22,2013,the epicenter of which was located in the Loess area,caused 95 deaths,2414 injuries,78,530 households,and 314,120 people lost their homes,and direct economic losses amounted to 17.588billion RMB,the most powerful earthquake in China in this century.The earthquake was the strongest in China in this century.The epicenter intensity of the earthquake wasⅧdegrees,of which the total area of the VI degree zone and above was 16,432km~2,which was heavily compared to an earthquake of the same magnitude.After the earthquake,a total of 64 strong shaking stations located in four provinces(regions)of Gansu,Shaanxi,Sichuan,and Ningxia were triggered,48 digital strong shaking stations recorded the strong shaking records of the mains motion,and 144 records of the3-component free field mains motion were obtained.This is the second time for China to obtain more comprehensive and high-quality digital strong-motion records after the Wenchuan earthquake on May 12,2008,and the Lushan earthquake on April 20,2013,and it is also the second time for China to obtain more abundant and comprehensive strong-motion records in the loess area.The strong vibration records contain a large amount of information related to earthquake damage,which is an important basis and information for analyzing the seismic effects and the damage characteristics of building structures in earthquakes.Especially in the absence of relevant seismic damage information in the pre-earthquake period,ground shaking parameters such as peak acceleration and peak velocity of free site earthquakes can be used as reference indicators for seismic intensity assessment and damage estimation.Therefore,the correlation analysis of ground shaking parameters and earthquake damage can quickly estimate the spatial distribution of earthquake intensity and damage loss,which is of reference value for improving the seismic protection capability in the area.Based on the strong motion records and seismic damage data obtained from the Minxian-Zhangxian 6.6 magnitude earthquake,this dissertation carries out research on the characteristics of the intensity distribution,housing damage,and local site damage amplification effects of the Minxian-Zhangxian earthquake by means of seismic damage analysis and strong shock record analysis;and explores the attenuation law of ground shaking parameters in loess and non-loess areas based on the main motion acceleration records of the Minxian-Zhangxian earthquake,focusing on the change of peak The study also explores the decay of ground motion parameters in loess and non-loess areas based on the main motion acceleration records,focusing on the changes of peak ground acceleration in loess areas with propagation distance and site conditions.(1)Based on the actual damage and earthquake intensity distribution of the Minxian-Zhangxian 6.6 magnitude earthquake,comparing the housing damage characteristics,damage levels,and casualties in loess and non-loess areas,it is found that the housing damage in loess areas is heavier than that in non-loess areas,generally one damage level higher,and the number of fatalities much higher than that in non-loess areas.Among them,the number of deaths due to house collapse in the loess area was 79,accounting for 83%of the total number of deaths,and the death due to house collapse and burial was one of the main causes of serious deaths in this earthquake.Meanwhile,the combined effects of the fault effect,loess site amplification effect,house earthquake vulnerability,rainfall,and continuous aftershocks were the main reasons for the severe earthquake damage.(2)The influence of propagation distance and site conditions on ground motion is discussed based on the 48 sets of strong motion records of the Minxian-Zhangxian 6.6magnitude earthquake;the distribution characteristics of peak ground acceleration between bedrock and soil sites are compared;the attenuation law of peak ground acceleration in loess and non-loess areas is initially analyzed.The results show that the ground motion of this earthquake is mainly in the east-west direction,and its attenuation law obeys the power function law.The mean horizontal peak ground acceleration function is(R is the epicenter distance),and the vertical peak ground acceleration function is(R is the epicenter distance),meanwhile,the peak ground acceleration in the loess area decays slowly compared with that in the non-loess area.(3)Based on the peak ground acceleration and peak ground velocity of free field horizontal ground motion obtained from the Minxian-Zhangxian 6.6 magnitude earthquake,contour clouds of peak ground acceleration and peak ground velocity were drawn and compared with the macroscopic intensity distribution map of the Minxian-Zhangxian earthquake for analysis;intensity assessment based on the horizontal peak ground acceleration and peak ground velocity of the earthquake area was conducted and compared with the macroscopic intensity for analysis to explore the correlation between the peak ground parameters of ground motion and macroscopic intensity.The results show that the V and VI degree zones of the contour cloud map based on peak ground acceleration and peak ground velocity do not exactly match the actual macroscopic intensity;the percentage of stations with an error of fewer than 2degrees when using peak ground acceleration to assess intensity is 70.00%.The percentage of stations with errors less than 2 degrees is 40.00%,indicating that the peak ground acceleration has a better agreement and correlation with the actual macroscopic intensity than the peak ground velocity.(4)The instrumental seismic intensities of each station were obtained according to the instrumental intensity calculation method of the China Seismic Intensity Scale(GB/T1772-2020),focusing on the differences between the macroscopic seismic intensities and the instrumental seismic intensities of the 10 stations triggered in the V and VI degree zones;the differences between the intensities of the seismic damage survey points and the instrumental seismic intensities in the VI degree zone were analyzed.The results showed that the stations with±1 degree difference between instrumental and macroscopic intensities accounted for 80.00%;the coincidence between instrumental intensities and the intensities of the surrounding survey points was66.67%.