Analysis On Microtremor Characteristics Of Engineering Site In Yantai City

The study of site dynamic characteristics is of great significance for the scientific development of urban earthquake disaster prevention measures and seismic design of building structures.The microtremor contains the dynamic characteristics of site soil,so the microtremor test can provide site predominant period and spectrum for the classification of site category and the seismic damage research.As one of the latest ideas of current study on the site dynamic characteristics,the microtremor test has been widely used in the work of urban earthquake zoning.Yantai City is located in the northeast of Shandong Peninsula,the North China earthquake,Tancheng-Yingkou earthquake belt on the central edge and the seismic fortification intensity is 7 degrees.Over the years the crustal movement is active,small earthquake constantly.In this paper,a large range of microtremor data acquisition is carried out in Yantai urban area,and the characteristics of ground motions such as the site predominant period are studied.The following results are obtained:1.The predominant period is one of the most important parameters reflecting the seismic dynamic characteristics of the site,there are many ways to get the data.The definitions of site predominant period in different codes are concluded in this paper,as well as its applications,calculation methods,advantages and disadvantages in seismic engineering are described,and that the microtremor tests is the most direct,the most convenient and the most economic way is concluded.2.In this paper,the test data of microtremor in many engineering sites in Yantai city are collected,and the distribution and general characteristics of the microtremor time course and spectrum of different sites in Yantai are obtained.The results show that: the time history curves obtained by microtremor tests are related to soil thickness,stiffness and other factors;the fluctuation spectrum structure of Yantai can be divided into three types: low frequency with multi peaks,double peaks or multi peaks and high frequency with sole peak;through the comparison of the three-component spectral structure of the same site,it is found that the spectral structure of the two horizontal components is substantially uniform.3.Based on the geotechnical investigation report of the site,the relationship between the microtremor characteristics and the soil structure is studied.The microtremor is dependent on the nature of the soil,and there are significant differences in site predominant period and spectrum structure of the site in different geomorphic units.The hard site has a lower frequency of microtremor than the soft site,and the presence of a weak interlayer is more complex than the single site.In the study area,the contours of site predominant period distribution of Yantai urban area are drawn through interpolation.The research results can provide reference for urban earthquake fortification and earthquake disaster reduction.