覆盖层厚度对远场长周期地震动能量特性的影响

Effect of Thickness of Overburden Layer on Energy Property of Far-field Long Period Ground Motions

选取汶川8.0级地震中陕西省6个台站的东西向地震动加速度记录,通过HHT计算了各条地震动和其IMF分量的Hilbert能量和输入能量,对比分析了覆盖层厚度对远场长周期地震动能量特性的影响。结果表明:随着覆盖层厚度的增加,地震动的HE峰值、输入能量和Hilbert能量平均周期T_(mE)逐渐增加;当覆盖层厚度大于400 m时,地震动能量主要分布在低频区域,具有显著的长周期特性;当覆盖层厚度为0或很小时,地震动能量主要集中在前2~3阶IMF分量中,多个IMF分量的HE峰值较大,卓越IMF分量对结构的影响较小;随着覆盖层厚度的增加,地震动能量主要集中在高阶IMF分量中,仅1~2个IMF分量的HE峰值较大,其余分量均很小,卓越IMF分量的平均周期T_(mE)和原始地震动十分接近,对结构的破坏起主导作用,应重点研究。

EW acceleration time histories recorded by 6 stations of Shanxi province in Wenchuan MS8. 0 earthquake are selected, Hilbert energy and input energy of both ground motions and each IMFcomponents are calculated through HHT, the effects of thickness of overburden layer on energy properties of far-field long periodground motions are analyzed comparatively. The results show that peak, input energy and Hilbert period #8 increase gradually with the increase of thickness of overburden layer; when the thickne400 m, ground motion energy mainly distributes in the low frequency region, and is of significant long period property. As the thickness of overburden layer is 0 or so little, ground motion energy mainly distributes in the first 2 ？3 IMF components, multiple IMF components are of large peak, and predominant IMF component has littleinfluence on structure; Accompanying the increase of thickness of overburden layer, ground motion energy mainlydistributes in the high-order IMF components, only 1- 2 IMF components are of large peak, other componentsare very small, the average period #mE of predominant IMF component is close to original ground motion. Predominant IMF component has leading role in the destruction of structure, and should be the focus of research.