Empirical Expression Of Basin Effects Coefficient And Their Application

Studies have shown that the Sichuan Basin is one of the important population agglomeration areas and economic centers in China,and studies have shown that the basin has high seismic risk,soft basin structure,fragile buildings,and dense population and wealth,which makes it face a greater risk of earthquake disasters,and its seismic safety needs urgent attention.Based on basin effect studies at home and abroad,the paper analyzes the applicability of the four sets of basin effect term models used in the 2018 edition of the US National Seismic Hazard Model in the Sichuan Basin in China,and the applicability of four sets of attenuation models with basin effect terms of NGA-West2 in the Wenchuan earthquake area and Lushan earthquake area in China was analyzed.At the same time,using the Wenchuan earthquake records of NGA-West2 database,the paper establishes a simple ground motion prediction model with basin effect terms in the Wenchuan earthquake area,and then obtains the relationship between amplification effect and depth in the Sichuan Basin.The magnification coefficient results obtained in this paper provide a reference for strengthening earthquake resistance and disaster reduction in this region and improving its disaster prevention and mitigation capabilities.It mainly includes the following and conclusions:1.The empirical expression method of basin effect coefficient and the definition method of basin depth are expounded.In this paper,the relationship between the amplification coefficient and depth of the Sichuan Basin is studied by using the ratio of the internal ground acceleration response spectrum of the basin caused by the basin structure to the acceleration response spectrum of the bedrock field point of the basin as the basin amplification coefficient.2.The latest progress on basin effects in the 2018 edition of the US National Seismic Hazard Model,and the applicability of the four models of NGA-West2 in the Wenchuan seismic zone and the Lushan seismic zone was studied.It was found that in the Wenchuan earthquake zone,the NGA-West2 models overestimated the longperiod ground motion(T≥1s)and underestimated the short-period ground motion(T≤0.5s),which was similar to the results of Wang et al(2010)and Zhang(2019).In the Lushan earthquake area,the NGA-West2 model overestimated the medium-and longperiod ground motion(T≥0.5s)and underestimated the short-period ground motion(T≤0.1s).That is,the NGA model overestimated the long-period ground motion(T≥1s)in this seismic area,which was similar to the results of Bai et al(2016),Ji et al(2016)and Zhang(2019).3.Using two sets of parameter data from different sources(finite fault model,distance parameters and other data corresponding to the same station),the applicability of four sets of attenuation relationship models of the 2018 edition of the US zoning map to the basin effect consideration in the Sichuan Basin was analyzed.In the same NGA-West2 prediction model,the parameter sources of the attenuation relationship are different,and the basin amplification effect and depth of the four sets of attenuation relationships in the Wenchuan and Lushan earthquake zones in the Sichuan Basin are still applicable to the same relationship.This shows that only one seismic area(within the Sichuan Basin)can be selected to study the amplification effect of the structure of the Sichuan Basin on the long-period ground motion.4.Taking Z2.5 as the basin depth,the basin effect terms Model1,Model2 and Model3 were added to the YW06 attenuation model and XY21 attenuation model by residual analysis method.Taking the prediction value of Model3 on the attenuation model as the reference value,it is found that the predicted value of Model2 and the residual distribution of Model3 considering the two sets of attenuation models are almost consistent.However,using Z2.5 as the basin depth parameter can only represent the shallow structure of the Sichuan Basin,and cannot reflect the actual basin basement shape.5.Taking the interface between Mesozoic and Paleozoic strata in the Sichuan Basin as the basin base,the relationship between the amplification effect of the Sichuan Basin structure on long-period ground motion and the depth of the basin was established.The maximum amplification coefficient of the Sichuan Basin is about 10,and the maximum value of the acceleration response spectrum of each period occurs near Deyang at the edge of the Sichuan Basin.Based on the regression results of the amplification coefficient of the Sichuan Basin,the zoning map of ground motion parameters considering the amplification benefits of the basin in Sichuan is obtained,which provides a basis for the future planning and earthquake resistance and disaster prevention of the Sichuan Basin,the consistent with the conclusion of Yu Yanyan(2016).6.Comparing the results of the Sichuan Basin amplification effect and depth with the results of Fu Changhua(2012)and Day et al(2005),due to our different definitions of basin depth,the magnitude of the basin magnification coefficient is not strictly comparable in the strict sense.However,from the trend of basin amplification effect,the conclusion of this paper is similar to that of Fu Changhua(2012)and Day et al(2005).7.Using the data on the thickness of the Quaternary and Neoproterozoic(N+Q)sedimentary layers in the Beijing-Tianjin-Hebei region established by the Sixth Generation Earthquake Parameter Zoning Map Preliminary Study Project,the results of the existing basin amplification effect study were used to obtain a ground vibration parameter zoning map for the Beijing-Tianjin-Hebei region,providing a reference for the Sixth Generation map to consider the effect of thick sedimentary layers.The...