地下地震动工程特性分析

为考察地下地震动的工程特性,选取美国加州强震观测计划(CSMIP)6个土工台阵的120条三分量地表和地下地震动为数据基础,分别对水平向和竖直向地震动的加速度幅值,规准反应谱,双规准反应谱,傅立叶谱,持时等工程特征进行了研究。结果表明,地震动加速度幅值随深度的增加而减小,在浅层的变化速度较快。规准反应谱明显受到场地条件和深度的影响。而不同场地不同深度不同分量方向的双规准反应谱之间差别甚小,双规准反应谱比规准反应谱表现出良好的一致性。最后,讨论了土层/基岩场地上台阵地震动的傅立叶幅值谱和地震动持时沿深度变化的特点。本研究揭示了地下地震动的一些工程特性,可以为地下工程结构的抗震设计提供参考依据。

Analysis on engineering characteristics of sub-ground motions

To study the engineering characteristics of sub-ground motions,three components of 120 ground motions on surface and in subsoil recorded by six CSMIP geotechnical arrays of the United States from 28 earthquakes were analyzed.The variations of amplitude of earthquake acceleration,normalized response spectrum(NRS) and bi-normalized response spectrum(BNRS) with depth were evaluated.It was concluded that,the amplitude of acceleration of ground motions decreased with depth and the attenuation rate was higher in the shallow strata than that in deeper ones.NRS was strongly related to site conditions and depth,while the BNRS had better consistency among all strong motion records than the conventional NRS under the influence of site condition,depth and motion component.Additionally,features of Fourier amplitude spectrum and variation of duration of ground motions with depth in Treasure Island were discussed.This study not only revealed the engineering characteristics of sub-ground motions,but also provided criterion in determining the seismic design for embedded structures and pipelines.