四川珙县M_s 5.4级地震斜坡地震动响应特征

Response Characteristics of Slope Seismic to Gongxian M_s 5.4 Earthquake in Sichuan, China

四川珙县Ms5.4级地震是长宁Ms6.0级地震第三大余震,在震中区诱发了多处滑坡和崩塌,研究坡体不同部位地震动响应特征对地震地质灾害预测和防治意义重大。通过在距离震源近的斜坡不同位置布置监测点,获取地震动参数及相关变化规律,对研究区域的坡体进行稳定性分析和研究。结果表明:地震在南北向的放大效应大于东西向,覆盖层土体最大位移达到了7.42 mm,与地震时南北向晃动强烈吻合;对比分析各个监测点的峰值加速度(PGA)、阿里亚斯(Arias)强度,覆盖层土体比高位基岩的放大效应显著;基岩地震波以低频为主,卓越频率为2~5 Hz,随着高程的增加对高频的地震波有过滤作用,在山顶3#监测点的阿里亚斯强度比山脚1#监测点(参考点)放大数倍,地震动能量强;通过该区域的抗震设计反应谱与监测反应谱对比分析,可以得出覆盖层土体和高位基岩地震动强烈,前者的宏观表现为覆盖层土体上老旧房屋毁坏严重,后者为高位基岩坡体滑坡和崩塌。

Gongxian Ms5.4 earthquake is the third largest aftershock after Changning Ms6.0 earthquake,and numerous landslides and rockfalls are triggered in the earthquake area.In order to detect the influence of seismic response on slope stability,the monitoring points at different positions of the slope close to the source were arranged to obtain the seismic motion parameters and related variation rules.The results show that seismic site amplification in SN-direction is obvious larger than that in EW-direction,whose displacement is also largest,especially for the soil monitoring point(7.42 mm),it is consistent with the strong SN-direction shaking during the earthquake;the soil could produce more obvious site amplification than bedrock by comparing PGA and Arias intensity of all monitoring points,and it could produce stronger dynamic condition;the resonance frequency of bedrock mainly concentrates on 2-5 Hz,and the resonance frequency decreases with the increase of altitude,the Arias intensity of mountain top(3#monitoring point)is obviously stronger than that of mountain foot(1#monitoring point);according to the comparison of seismic design response spectrums and monitoring response spectrums,the soil and bedrock could occur geohazards easily,which threaten to building stability.