渭河盆地中土层场地对地震动的放大作用

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...

Amplification effects of soil sites on ground motion in the Weihe basin

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.