汶川地震远场地震动场地相关性与分析方法评价

Evaluation of site dependence and methods for site analysis based on far-field ground motions from the Wenchuan earthquake

为考查远场地震动的场地相关性并评价一些场地特性分析方法的适用性,采用不同方法对汶川地震山东省12个远场台站的强震记录进行了分析.选取台站分别位于按建筑抗震设计规范(CBC)场地划分中的Ⅰ—Ⅲ类场地上.地震动记录的分析方法包括傅里叶幅值谱法,地震反应谱法,水平与竖向谱比率法,参考点谱比率法,以及尾波分析等.结果表明,按傅里叶幅值谱法,地震反应谱法,水平与竖向谱比法计算得到的卓越周期均远大于台站场地的卓越周期,不同方法得到的结果之间也有较大差别,且主要反映长周期地震动的卓越频率;参考点谱比率法的结果未反映地震动的卓越周期,也与场地的卓越周期差别较大;对完整记录尾波分析所得的结果比较接近场地的卓越周期.希望本文能为考虑远场地震作用时设计谱的建立,以及场地特性估计时地震动分析方法的选取提供参考依据.

To examine site dependence and evaluate the applicability of methods for site analysis of far-field ground motions,we present an analysis of the frequency content estimated with different methods using strong ground motions recorded at twelve far-field stations in Shandong Province during the Wenchuan earthquake.The stations are located in sites with soil profiles ranging from class Ⅰ to Ⅲ according to China Building Code for Seismic Design（CBC）.Approaches used include Fourier amplitude spectrum,earthquake response spectrum,spectral ratio between horizontal and vertical components（H/V）,spectral ratio based on reference site,and coda wave analysis.Results show that：predominant periods obtained by Fourier amplitude spectra,response spectra and H/V ratio methods are all evidently larger than site dominant periods,and different methods yield different periods,which mainly reflect the frequency content of long period components;predominant periods obtained by the spectral ratio based on reference site approach can neither illuminate predominant periods of ground motions nor efficiently present site features of the motions;coda wave analysis results in a period colse to the site predominant period for stations with good quality recordings.It is expected that this study will be useful for evaluating far-field effect in constructing seismic design spectra and in selecting methods for ground motion site analysis.