| The shallow overburden soil layer has an important influence on the amplitude,spectral characteristics and duration of strong ground motion,which is mainly manifested as the amplification of ground motion by the site.The results of previous earthquake damage investigations show that local site conditions have an important influence on the characteristics of ground motion and the severity of earthquake damage.Even in two regions with similar epicentral distances,the differences in earthquake damage caused by different site conditions are often very large.Therefore,effectively considering the influence of site conditions on seismic damage is an important research topic in the field of seismic design.In the field of earthquake engineering,the site PGA amplification factor can reflect the influence of the site soil layer on the ground motion intensity,and plays an important role in the study of ground motion attenuation relationship,earthquake early warning of major engineering projects and structural seismic design.In order to reflect the influence of site conditions as much as possible in the work of earthquake prevention and disaster reduction,it is an important task to find reasonable characteristic parameters to more reliably characterize the amplification effect of site on ground motion.The basic period of the site,the average shear wave velocity near the surface,the average change rate of the shear wave velocity with depth and the inter-layer impedance ratio are the representative characteristic parameters of the site soil layer,and also the important basis for evaluating the site conditions.The general variation law between these parameters and the site PGA amplification factor is explored,and the optimal model of the site amplification factor is established to provide a more reasonable design theory for the seismic design of the engineering structure.In this paper,158 stations conforming to the one-dimensional layered site model and the corresponding 7978 sets of ground motion records are selected from the KiK-net network,and the PGA amplification coefficient of the selected stations is given.Secondly,the site characteristic parameters used in this study are introduced in detail,and its basic definition and calculation method are given.Next,the single parameter model analysis is carried out according to the selected site characteristic parameters and the site PGA amplification coefficient.Finally,based on the basic period of the site and the average shear wave velocity of the near surface,the two-parameter analysis is carried out with other site characteristic parameters.The main research work and research results of this paper are summarized as follows:(1)According to the research content,the selection principle of site and ground motion records of KiK-net station in Japan is given,and the data characteristics of the selected stations are analyzed.The ground motion records are processed,and the PGA amplification coefficient of each group of ground motion is calculated.After eliminating the abnormal values,the PGA amplification coefficient of the selected station is given by taking the average value.(2)The site characteristic parameters used in this study are introduced,and the basic definitions and calculation methods of these site characteristic parameters are given.The generalized impedance ratio which can reflect the inhomogeneity of the wave velocity structure of the whole site is constructed,and the factors such as soil thickness,depth and sequence structure are considered,and the corresponding calculation formula is established.(3)According to the selected calculation method,the data characteristics of the results of the characteristic parameters of each site are analyzed.Through correlation analysis,the general variation law between the site PGA amplification coefficient and the site characteristic parameters is grasped.The results show that only Vs30 has weak characterization ability for site amplification.The generalized impedance ratio constructed in this paper has the highest correlation with the site PGA amplification coefficient under the condition of considering the depth range of 50 m.(4)The correlation between the fitting residuals of the single-parameter model of the basic period of the site and the near-surface average shear wave velocity and the characteristic parameters of other selected sites is analyzed.Based on these two parameters,the two-parameter model analysis is carried out with other site characteristic parameters.The results show that the two-parameter model of T0 with α5,50m and Vs30 with α3,30m has the highest correlation with the site PGA amplification coefficient,and the correlation is higher than that of the single-parameter model. |
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