New V_S30 Estimation Model And Its Application On China Seismic Site Classification And V_S30 Map For China’s Mainland

Site amplification is an vitality research field in earthquake engineering.The shear-wave velocity acts as the most common parameter representing site condition for the engineering characterization of site amplification.At the international level,the time-averaged shear-wave velocity to 30 m(VS30)is widely used as the representative parameter of the site condition.While in the practices,especially for the applications like seismic zonation,earthquake insurance,etc.that needs to be applied in the large scale,measuring the VS30 value site by site is impractical.And when a ground motion prediction equation is fitted,it is a common case that a number of strong ground motion stations are lacking of VS30 values.So there are requirements of using models to estimate VS30 at any points in the earthquake affected or potentially affected area.These kinds of models can be categorized into two classes,one is using shallow borehole profiles to estimate VS30 at the same site.In this research,they are named as VS30 extrapolation model;another is to estimate VS30 through correlations with geological,geomorphologic or topographic proxies.In this research,they are named as VS30 proxy model.From 2000,plenty of works were carry out in developing these two classes of models.But previous researches are all have following limitations: 1.Past VS30 extrapolation model studies are relied only on shallow borehole shear-wave velocity(VS)profiles to estimate VS30.Other useful information like geological profile and location slope are omitted;2.Most previous VS30 proxy models do not consider the effect of data spatial structure,and the resulting maps effectively ignore the known VS30 value at the measurement locations;3.When developing the models,the bias of the data and spatial clustering effect of the data are ignored.In this study,over 10 thousand of boreholes in the China’s mainland are compiled to build a new borehole profile database(BPDB).In this study,a new parametrical VS30 extrapolation model is developed.The new model accounts for the additional parameters including location slope,geologic age,and geotechnical class to enhance the model performance.In this study,a new VS30 proxy model using topographic slope as the proxy are developed.The new model is based on Co-Kriging theory and effectively maintains the consistence of estimation results and the measurement data.The new model shows better performance comparing to other previous topographic slope based models.In this study,a data transformation method is proposed to quantify the sample bias comparing to the sample population.In this study,a new data spatial declustering method is also proposed to applied on semi-variogram fitting in the kriging method.Moreover,this study systematically analyzes the effect of the parameters of location slope,geologic age,and geotechnical class on the borehole VS profile.The performance of five existence VS30 extrapolation models are compared and analyzed in this study.This study also scrupulously reviews the China building seismic design code provisions especially provisions for site class II based on real data.In this study,the statement of using exogenous data to develop local VS30 proxy model will lead to large bias is proposed.A new BPDB data structure is introduced.In the perspective of application,using upper mentioned new models and theories,the quantitative transformation relations of Sino-US site classification systems in building seismic design code provisions is built,a VS30 map for China’s mainland is developed.