Improvement Of Traditional Spectral Ratio Method Based On Strong Earthquake Records

At present,the most commonly used method to calculate the site response is the traditional spectral ratio method.This method has certain shortcomings,which requires the research site and reference site with relatively close distance.When the distance difference between the two sites and the source is too large or the medium characteristics are too different,the traditional spectral ratio method will produce large errors in the calculation process.Considering the absorption and attenuation effect of medium on seismic wave,two improved spectral ratio methods are proposed in this paper,and the calculation formula and calculation process are given in view of the shortcomings of traditional spectral ratio methods.The seismic records collected by several stations in Weihe Basin during the Wenchuan earthquake are used to verify the first improved spectral ratio method.The key of this method is to calculate the absorption attenuation coefficient.Then,the site response of 25 soil layer stations in Weihe Basin is calculated by the traditional method and the improved method.The site magnification times calculated by the improved spectral ratio method all have a peak value below2 Hz,and these peaks are mostly the maximum value.The frequency of the site magnification peaks calculated by the traditional spectral ratio method is mostly higher than 2Hz.Combined with the analysis of the soil layer thickness in Weihe Basin,the existing problems of the traditional spectral ratio method are confirmed,and the reliability of the improved spectral ratio method can be confirmed.The seismic records collected by several stations in Chengdu Plain during the Wenchuan earthquake are used to verify the second improved spectral ratio method.The key of this method is to calculate the quality factor Q value of the medium in Chengdu plain through the seismic data of bedrock stations.The traditional spectral ratio method and the second improved spectral ratio method are used to calculate the horizontal site response of soil stations respectively.The site response of seismic stations in the soil layer near Chengdu calculated by the improved spectral ratio method is very small,which proves that the overburden in Chengdu area has damping effect.The Chengdu area is very close to the epicenter of Wenchuan earthquake,but the earthquake damage is small,which corresponds to the low site response calculated by the improved spectral ratio method,which proves the effectiveness of the improved method.This paper has 17 figures,4 tables and 89 references.