中文摘要：

采用汶川地震强余震26个强震动台站记录，基于H/V谱比法，计算台站场地的强、弱震作用下场地卓越频率之比Rfp和体现强、弱震作用下场地H/V谱比曲线差异程度的DNL，进而识别并分析场地非线性反应特征。结果显示，Rfp、DNL与PGA之间存在显著相关性；其中10个台站出现明显的场地非线性反应特征；大部分台站发生场地非线性反应的PGA阈值为100cm/s2，部分为50cm/s2；实例证明，因某些台站不易通过H/V谱比法识别场地卓越频率，因此采用Rfp识别场地非线性反应具有一定局限性。

英文摘要：

There are so far not any studies systematically focusing on the nonlinear site response for the strong aftershocks of Wenchuan earthquake.The site responses of the26strong-motion stations were estimated using their1539recordings collected in the Wenchuan earthquake sequence based on the horizontal-to-vertical spectral ratio(HVSR)method.The nonlinear site response was identified by the two indicators,Rfp(the ratio of the predominant frequency of the site response between the strong and weak ground motion),and DNL(the difference degree of HVSR curves which are calculated with strong and weak ground motion data).The both indicators have significant correlations to the peak ground acceleration(PGA).Obvious evidences were found for10strong-motion station to show nonlinear site response.It shows that PGA>100cm/s2may be a threshold for ground motions generating a shift of the site response from linearity to nonlinearity.The indicator,Rfp,has some limitations to indentify the nonlinear site response in some cases that the site predominant frequency is difficult to be clearly identified.