Attenuation Relationship Of Small And Medium Ground Motion In Sichuan Province Considering Different Site Types

Since 2008,China Digital Seismograph Network center has been running,there have been many strong earthquakes in Sichuan Province not only provides a lot of high quality fixed stations record,also contributed a lot of near field temporary stations record,that provides a good data base for our country to study the earthquake attenuation relation of Sichuan region.In the past research,a large number of near field temporary stations record can't be applied to the attenuation relationship,because the site type of temporary stations can't be classified by conventional method.This paper will take record of fixed station and Wenchuan aftershock temporary stations as the data base,and apply the horizontal-to-vertical(H/V)spectral ratio method to classify the site type of temporary stations,and analyze the difference of the fixed stations data and temporary station.Then apply the data of temporary stations to the attenuation relationship regression in Sichuan area.The specific work is as follows:We collect drilling data and Vs30 data of fixed stations in Sichuan area,and classify the site types of fixed stations according to the code for seismic design of buildings and the correspond Vs30 range in different types of code.Based on the predominant period and different sites characteristics of the response spectrum,the Wenchuan aftershock temporary stations site types classified by H/V spectral ratio method.We collect the strong motion records of 125 stations located in the Sichuan area within 200 km from the epicenter of Ms3.5-6 in 2008-2015 years.The data distribution characteristics of different site types and magnitudes are analyzed.The type?sites are concentrated in the near field region,while the type?sites are more evenly distributed in each epicentral interval.We analyze distribution characteristics of acceleration peak(PGA)and response spectrum.Then we compare average response spectrum of fixed station after removed geometric diffusion with temporary station.The response spectrum of temporary station is higher than that of fixed station in long period.The data were divided into two groups: a set containing only stationary station records;a group containing both stationary and temporary station records.According to the characteristics of data,the model was adjusted and the regression analysis between two groups of data was carried out by using random effect method.By comparing the regression parameters and results of the two bins of data,it was found that the within-residual of the attenuation get bigger after temporary station data added.By analyzing the residuals of PGA and reaction spectrum in each magnitude,it is shown that the attenuation relation can well estimate the ground motion PGA and response spectrum of fixed stations at different magnitudes,but underestimate slightly ground motion parameters of the temporary station.By comparing the results with others researchers of attenuation relationship in Sichuan province,we found the results of PGA are similar,but underestimate slightly response spectrum,generally speaking the attenuation of this research can better reflect the characteristics in Sichuan region.