复杂区域地形条件下台地地震动放大效应研究

Amplification effect of plateau ground motion under complex regional terrain conditions

针对不规则地形地震动放大效应的相关规定大多以孤立地形为对象,但山区地形常以群山形式存在,相邻地形会影响地震波传播,从而改变地表运动规律。因此研究非孤立地形的地震动放大效应对山区建筑的抗震设计及提升震后灾害评估准确性具有重要意义。首先阐述了在泸定6.8级地震中磨西台地不利地段发生的典型地形放大效应。随后利用仿真手段深入探索了复杂区域地形(山脊、峡谷)对台地地震动放大系数的影响。从放大系数空间分布、加速度傅里叶谱及幅值比的角度进行量化研究,并通过大量变参分析获得复杂区域地形对台地表面的运动规律。结果表明,在某些情况下《抗规》低估了台地地形效应,放大系数建议值难以保证结构“大震不倒”,需进行调整和细化。此外,相邻山脊和峡谷对台地表面均有明显影响,不应被忽略,因此建议相关规范增加调整系数来考虑相邻地形之间相互影响。

The relevant regulations of amplification effect of irregular terrain seismic motion are all focused on isolated terrain,but mountainous terrain often exists in the form of mountains,and adjacent terrain can affect propagation of seismic waves to thereby change motion laws of ground surface.Therefore,studying the seismic amplification effect of non-isolated terrain is of great significance for aseismic design of mountainous buildings and improving the correctness of post-earthquake disaster assessment.Here,firstly,the typical terrain amplification effect occurred in the unfavorable section of Moxi Plateau during 6.8M earthquake in Luding was elaborated.Subsequently,simulation method was used to deeply explore effects of complex regional terrain of ridges and canyons on the amplification factor of ground motion on plateaus.Quantitative study was performed from the perspectives of amplification factor spatial distribution,acceleration Fourier spectrum and amplitude value ratio,and fluence laws of complex terrain on plateau surface motion were obtained with extensive parametric analysis.The results showed that in some cases,the"Code of Resistance"underestimates the platform terrain effect,and the recommended amplification factor value is difficult to ensure structures being not to collapse during a major earthquake,and adjustment and refinement are required;in addition,adjacent ridges and canyons obviously affect plateau surface and should not be ignored;thus,it is recommended to increase adjustment factors for considering the mutual influence among adjacent terrains in relevant regulations.