【摘要】 土层场地对地震动的影响较大,建(构)筑物的选址及其抗震设防必须考虑土层场地的放大作用,以避免或减轻其震害.汶川地震中,布设在渭河盆地中的数字强震动台网共有27个台站(包括2个基岩台站和25个土层台站)获得良好的主震加速度时程.利用这些加速度时程,选择汤峪台做为参考场地,基于考虑几何衰减的传统谱比法分析研究了25个土层场地的放大作用.结果表明:(1)汶川地震中渭河盆地土层场地上的加速度峰值(PGA)有随震中距增加而减小的趋势,且与土层的厚度无关.(2)根据汶川地震中渭河盆地土层场地的加速度反应谱特征及其对地震动的放大作用特征,渭河盆地的土层场地可分为3类:深厚、中厚和薄土层场地.而且,深厚、中厚和薄土层场地分别对地震动的低频、1 Hz附近和高频分量放大作用显著;值得注意的是,深厚土层对地震动的高频分量也有一定程度的放大,只不过相对于低频分量的放大作用较小.(3)汶川地震中渭河盆地的土层场地对不同方向地震动的放大作用不同,且有EW>NS>UD的关系.(4)汶川地震中从宝鸡到眉县沿着盆地边缘分布的Ⅶ度烈度异常区是盆地边缘效应和土层场地对地震动放大作用共同作用的结果.更多还原

【Abstract】 Effects of soil sites on ground motion are relatively serious,their amplification effects on ground motion must be considered in site selection and seismic fortification of buildings to prevent or mitigate seismic hazard of buildings.The mainshock’s acceleration time histories of 27 stations(including 2 bedrock stations and 25 soil stations)in the digital strong motion seismograph network installed in the Weihe basin in Wenchuan great earthquake were recorded. Utilizing the acceleration time histories,the amplification effects of 25 soil stations are studied and analyzed by traditional spectral ratio method with geometric attenuation while Tangyu station is seclected as reference site.The results are as follows.(1)Peak ground accelerations(PGAs) on the soil sites in the Weihe basin in the Wenchuan great earthquake have decreasing trends with the epicentral distances regardless of the soil thickness.(2)According to the characteristics of both acceleration response spectra of soil sites and amplification effects of soil sites on ground motions in the Weihe basin in the Wenchuan great earthquake,the soil sites in Weihe basin can be classified into 3 categories,i.e.,deep,intermediate,and shollow soil sites,which respectively amplifies the low frequency components,components in the vicinity of 1 Hz,and high frequency components of ground motions significantly.It is noteworthy that high frequency components of ground motions are also amplified to a centain extent for deep soil sites,but the amplification factors of high frequency components are smaller than those of low frequency components.(3) The amplification effects of soil sites on different direction(i.e.EW,NS and UD)ground motions in the Weihe basin in the Wenchuan great earthquake are different.Generally,EW>NS> UD.(4)Abnormal area of intensity Ⅶ along basin edge from Baoji to Meixian in the Weihe basin in the Wenchuan great earthquake resulted from combined amplification effects of both soil sites and basin edge effects on ground motions.更多还原