Study On Site Effect Based On Strong Motion Data From KiK-net In Japan

Site effect is one of the important research topics of engineering seismology,geotechnical seismic engineering and seismology.For near-fault ground motion simulation,ground motion prediction equation establishment,seismic damage assessment of earthquake disaster areas,seismic subdivision,and location selection of buildings,its seismic fortification has important theoretical significance and engineering application value.This paper uses the strong motion observation data of KiK-net network in Japan to carry out the research on site effect.The main research work and the results obtained are as follows:1.The 646 stations with complete borehole test data in the KiK-net seismic network in Japan are respectively in accordance with Chinese "Code for Seismic Design of Buildings"(GB50011-2010),the United States National Earthquake Hazards Reduction Program(NEHRP)and Zhao et al.(2015)which based on the classification method of the basic period of the site,the site type is divided.The results show: the venue types of the stations in KiK-net are mainly type II in China,type C in the United States,and SC I,SC II and SC IV in Zhao et al.(2015).Other types of venues are relatively few.2.Using the ground motion data recorded by 180 stations in KiK-net from 2000 to2019 and using the uphole/downhole spectral ratio method: first estimate the amplification effect and basic period of the site based on the weak motion data,and give the site magnification effect models of different site types;then study the basic period of the site and its corresponding magnification coefficient with the intensity of ground motion.The results show: as the site becomes softer,the basic period moves in the direction of the long period,and the softer the site,the more significant the amplification effect on low-frequency components;as the intensity of ground motion increases,the basic period of the site also moves in the direction of the long period.The amplification factor of the corresponding frequency is smaller than that of weak vibration.3.Based on the method of Anderson and Hough(1984),a new method for determining kappa parameters is proposed.That is,first use the 0.4Hz Parzen window to smooth the acceleration fourier spectrum,and then you can accurately select the starting point of the fast falling section of the fourier spectrum.Third,the kappa value can be obtained by regression analysis of the data between the starting points.The reliability of this method is verified by the ground motion data of 14 stations.Using this new method,this study estimated the kappa parameters and their k₀ values of 646 stations in KiKnet,gave the k₀ values of different site types;and studied the k₀ changes with the thickness of the soil layer and the change with V_S30.The results showed that k₀ increased logarithmically with the increase of soil thickness,and decreased logarithmically with the increase of V_S30.