Study On Estimation Of Site V_S30 For Ground Motion Stations And Site Amplification Model

Site condition has a significant impact on ground motion,and is an important factor while determining seismic design ground motion parameter.Therefore it is useful to investigate the nature of influence by site condition on ground motion.It is generally known that the ground motion is result from comprehensive function of multiple factors including feature of source,propagation path and site condition.The site amplification of ground motion can reflect site condition so well that the ground motion recordings can provide foundation of data to study the nature of influence by site condition on ground motion.Despite the rapid increasing of strong motion recordings around the world,the usage of them were severely restricted due to the lack of site condition data of some strong motion stations.In order to change the situation,a new method by using strong motion recordings combined with shear wave velocity data of some stations to estimate V_S30 of strong motion stations with bottom depth less than 30 m or without any shear wave velocity is proposed.The reliability of the developed method is validated through comparison of the estimated value with the measured value from boreholes of the stations in Japan,California and Western China,respectively.Applying the approach to Western China to estimate the V_S30 values of parts of stations.Based on the V_S30 determined by the method proposed,the empirical site amplification models is built.The main content of thesis are as follows:（1）Based on the site amplification factors of strong motion stations obtained by generalized inversion technique（GIT）,the relationship of quarter-wavelength average velocity of the two stations is built using square root impedance（SRI）approach.In the light of the relationship of quarter-wavelength velocity of two stations and shear wave profile of one station,the V_S30 value of the target station without any shear wave velocity can be obtained.The reliability of the developed method is validated through comparison of the estimated value with the measured value from boreholes of the stations in Japan,California and Western China,respectively.Applying the method proposed to Western China,V_S30 values of stations are evaluated.（2）Based on the shear wave profile of superficial layer（<30 m）and site amplification curve obtained by generalized inversion technique（GIT）for strong motion stations,the V_S30 value of the station whose bottom depth does not reach 30 m can be obtained.The reliability of the developed method is validated through comparison of the estimated value with the measured value from boreholes of the stations in Japan,California and Western China,respectively.This method can avoid the dependence of empirical model to estimate V_S30.Applying the method proposed to Western China,V_S30 values of soft stations whose bottom depth do not reach 30 m are evaluated.（3）In order to develop a relationship between V_S30 and the site period T0,the data of T0 and V_S30 of stations from Western China were used in this study.For the strong motion stations from Western China,which do not meet the requirement in the GIT method and have no shear wave velocity data,the empirical model proposed by this paper is used to estimate V_S30 value of them.Through comparison with the other methods,results indicated that,compared with the V_S30 values predicted from topographic slope,the V_S30 values obtained by the method in this paper shows stronger correlations with the site amplification;the effect of evaluated V_S30 on the site amplification reflects the nature of influence by site condition on ground motion.（4）To investigate the effect of site amplification on ground motion for Western China,site shear wave velocity profiles from this area are used.Through equivalent-linear site response analysis method the influence of nonlinear soil effects on site amplification factor is studied.Combined with comprehensive analyses of strong motion data from this region,the site amplification model is developed.It is shown that this model can reflect well the influence of site condition on ground motion in Western China.By use of ground motion prediction equation（GMPE）including the model in this paper,the spectral acceleration is evaluated.It is clear that the outcome obtained by the GMPE can reflect the influence of soil nonlinearity on the spectral acceleration.