Based on analysis of the shear wave velocity data of 823 boles from the northern,eastern,southern,northeastern and northwestern areas of China,we studied the difference of the equivalent shear wave velocities calculated with the soil-and-rock depths of 20m and 30m,respectively.We also discussed the features and differences among the Chinese,American and European seismic regulations in site classification using the parameter of equivalent shear wave velocities of boles.Our results indicated that:① The equivalent shear wave velocity will increase about 10 to 60m/s when we increase the calculation depth of soil-and-rock from 20m to 30m.The average increase is about 24m/s.② Comparing with the American and European seismic regulations,the current Chinese seismic regulation(GB 50011-2001)requires the information of the equivalent shear wave velocities calculated with the soil-and-rock depths of 20m,as well as the depth of the overburden in the site when classifying the site.However,it is usually difficult to obtain the usable overburden depth in many engineering sites to serve the site classification.Therefore,it is necessary for us to use for reference of American and European seismic regulations to increase the depth of soil-and-rock when calculating the equivalent shear wave velocity so as to get a more reliable parameter to serve for the site classification.

Two kinds of site classification methods commonly used in earthquake engineering are analyzed in this paper.One is standard methods stipulated in seismic codes,and used to determine the site effects on seismic parameters for the seismic resistance of structures,the site classification methods and site indexes in seismic codes of China,United States,Europe and Japan are presented,and the problems about site index are discussed,such as the calculation method and depth of shear wave velocity,the choice of initial layer,the grade of overburden thickness,etc.Then some suggestions are put forward for the new generation of seismic code in China.The other kind of site classification methods is used to predict site effects on a large scale for a regional seismic hazard prediction.The popularly studied methods based on geology,topography and geomorphology are described in detail.The common character of this kind of methods is to find an easily obtained macro index,and to summarize the rules between the macro index and the site index in seismic codes(shear wave velocity in most cases),and then the regional site category zonation can be delineated.The response spectrum methods of ground motion are also presented here,such as RSS(Response Spectral Shape)and HVSR(Horizontal-Vertical Spectral Ratio),they can be used in areas with abundant ground motion records.Finally the advantage,limitation and applicable scope of these methods are discussed.