| The site effects has always been a hot topic in the field of engineering seismology,and the local site conditions have a significant impact on ground motion characteristics,which had been demonstrated in a large amount of seismic damage investigation and theoretical research.However,the strong-motion records are the basis for quantitative analysis of site effects,and the macroseismic damage investigation provides the most intuitive understanding about it.Therefore,the more effective way to study site effects is to combine these two informations.In the 2008 Wenchuan earthquake,the China National Strong Motion Observation Network System captured a large number of strong-motion records in the main shock and aftershcoks.At the same time,after half a year it occurred,the strong-motion stations investigation team of the Institute of Engineering Mechanics,China Earthquake Administration who went into the earthquake region for surveyed the observation environment and the damage about the buildings which around the strong-motion stations;and laid microtremor observation points around the station according to the local topography,then conducted a series of consecutive microtremor observation,which help us obtained a wealth of investigation data.And this data provides a good opportunity for us to study the site effects of the Wenchuan earthquake.Therefore,this paper based on the above database,study the site effects of the Wenchuan earthquake,and the main work and conclusions are as follows:1.Studied the amplifying action of slope terrain by using horizontal Fourier amplitude spectrum of microtremor data.The results showed that the slope terrain will have a significant impact on the strong motion observation,and this amplification effect increases with increasing vertical distance from the observation point to the base of slope terrain,and which reaches a maximum in the platform of it.Moreover,the amplification effect of observation point which located on the edge of the platform is larger than the one which located inside of the platform.2.Analyzed the effect of valley terraces on strong motion observation by using the spectral ratio method and microtremor data.The results showed that the valley terraces can result in an amplification effect or a lessening effect in different frequency bands,which is particularly prominent in the high frequency part,and with the increase of valley terraces series the ground motion may have a lessening effect affected by the complex geological environment underground it.Studied the site characterization around the station by using the FASR curve of Wenchuan aftershocks records and the HVSR curve of microtremor data,and we found that they obtained similar results aboutthe site predominant period which help us to verify these two methods for determining the site predominant period have a good consistency.3.Studied the basic approach of strong-motion records on the results of site characterization.Discusses the necessity for P-wave and S-wave data to take Taper Preprocessing before we use it,and study the impact of the smoothing effect of Parzen windows with different bandwidths to FASR curve.The results showed that the Parzen window with a 0.5Hz bandwidth could be sufficient enough to meet our smoothness requirements for FASR curve.To study the similarities and differences between FASR curve of full-time course,P-wave,S-wave and the HVSR curve of full-time course.We found that the degree of similarity: S wave > full-time course > P wave,and the predominant period of FASR curve of full-time course and S-wave is similar to the predominant period of HVSR curve of full-time course,but the result of P-wave is poor. |
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