Estimation Of Site Effects Based On KIK-net Strong-motion Seismograph Network

Site amplification has an important influence on the seismic design of building structure.In the fifth generation of Chinese seismic zoning map(GB18306-2015),the acceleration coefficient of the ground motion peak acceleration is considered.The code for seismic design of buildings(GB50011-2010)has been partially revised,and the code for seismic design of buildings GB50011-2010(2016 Edition)also reflects this result.Generally,the standard spectral ratio method(SSR)is the most common method to study the site amplification factor,which is obtained by using the spectral ratio of the strong earthquake records in the soil layer and the nearby reference bedrock site.The problem with this method is that it is difficult to find the real bedrock site,because the weathering layer on the bedrock surface is ubiquitous,and the reference bedrock site is very close to the soil layer.Due to the great influence of site conditions on ground motion records,as well as representative and extensive station data is limited,which makes the traditional SSR can not be directly applied to the KiK array in the coverage area and also can not obtain the amplification factor.At the same time,each station must consider the source,transmission,each site and other factors.There are also differences in each drilling depth of bedrock,soil layers medium velocity and other parameters,but also did not consider the seismic reflection wave in soil medium between the impact.These will have an impact on the results of the traditional SSR.In this paper,the above problems are studied.The main contents are as follows:Frist,the data in this paper according to the Japanese KiK-net strong motion observation network from January 2000 to December 2015.The magnitude is higher than 4.5,the focus depth is less than 50 km,the epicentral distance is less than 100 km.At the same time,the signal to noise ratio of each data is limited,and the data can be processed without filtering.In the end,1233 groups of records are selected to provide a solid foundation for the research work in this paper.Second,this paper selects the Japanese KiK-net vertical drilling records(GIFH09)and a simple site information.The seismic response of the soil layer is simulated by using the linearization method.The ground motion at different depths are calculated.Also the acceleration response spectrum of different sites are obtained.So the general law of depth correction factor is obtained.Then,the acceleration response spectrum ratio method and the Nakamura method(single spectral ratio method)are adopted by selected 8 pairs of KiK-net stations.Through the qualitative analysis of the two methods of spectral ratio BSR_F(underground bedrock surface and underground Fourier spectrum ratio of Fourier spectrum)is greater than the standard spectral ratio SSR.Then,considering all the Ki K-net site surface transfer function TF and the borehole transfer function BTF,compare them with the BSR_F.Based on the above results,a simple and effective depth correction factor is proposed.Finally,comparing the results of SSR,BSR_F and depth correction,it is found that the results of the depth correction BSRc_F are very close to the SSR,which can be used to replace the standard spectral ratio SSR to calculate the site amplification factor.Finally,by summarizing the research status and development trend of domestic and foreign site adjustment coefficient and using Japanese KiK-net actual seismic observation statistics the ground rules.Then by the above depth correction factor,Chinese site classification standards and the method of foreign research are adopted.And,the site adjustment coefficient of the site classification standard of our country is obtained.So the value of the adjustment coefficient is given.