黄土塬地震动响应特征分析

2008年汶川Ms8.0级强烈地震对远离震中的黄土塬地区造成了较为严重的破坏，局部场地的震害和地震动放大效应显著。以典型黄土塬场地为对象，应用地形台阵流动观测和有限元计算方法，系统开展强震动作用下黄土塬边坡场地动力响应特征研究；应用大型振动台模拟试验和数值计算方法，重点探讨黄土塬平台场地在汶川地震作用下地表加速度响应随覆盖层厚度、地震动强度的变化规律以及对建筑结构的潜在影响。结果表明：黄土塬边坡顶部存在低频但较高放大系数的现象，可能与斜坡高差与入射波波长之比密切相关；大角度（60°～70°）黄土塬边坡对地震动的放大效应十分显著，坡顶加速度峰值（PGA）放大可达2倍，反应谱卓越周期放大可达5倍；较厚黄土塬平台场地加速度放大可达2倍以上，地震烈度增加1度，对于场地上固有周期0.7～2.0 s和周期大于3.0 s的建筑物地震反应将显著增加。

Earthquake response characteristics of loess tableland

The 2008 Ms8.0 Wenchuan earthquake had caused serious damage to structures in loess tableland region far away from the epicentre, the earthquake damage and the amplification effects of ground motion on local sites were significant. Using the typical loess tableland as the object of investigation, the dynamic response characteristics of loess tableland slope under the action of strong vibration were systematically studied by applying mobile ground motion observation arrays and numerical analysis. Based on large-scale shaking table test and numerical simulation, the change rules of surface acceleration responses of loess tableland with different thicknesses under different actions of Wenchuan earthquake were analyzed, and the potential effects on the earthquake damage were studied. The results show that: 1) The phenomenon of low predominant frequency corresponding to high peak ground acceleration (PGA) amplification at the top of loess tableland slope may be related to the ratio of slope height difference to incident wave length. 2) The loess tableland with a slope gradient ranging from 60o-70o has the most significant amplification effects on ground motion. The PGA on top of slope can be amplified by 2 times, the predominant period can be increased by 5 times. 3) The amplification effects on ground motion are predominant for thick loess tableland, PGA horizontal amplification coefficient potentially subject to an increase by 2 times and seismic intensity by 1 degree. 4) Along with the increase of loess thickness, the predominant period of response spectrum increases, so that buildings with natural period ranging from 0.7 to 2.0 seconds or greater than 3 seconds will undergo obvious horizontal amplification effects.