The surface vertical vibrations induced by metro do not decay monotonously.There is a region called the local amplification region (LAR) with an offset to the epicenter,In-situ vibration measurements were conducted at three representative sites passed by buried metros.The results showed that there are LARs for each vibration attenuation curve of 3 sites;the first LAR defined as the major amplification region (MAR) is the most siginificant and appears with a distance of about one burial depth from the epicenter;base on the theory of elastic wave propagation and numerical simulation of finite element,the major influence factors on the MAR are ① the superposition effect of incident and reflected waves within the near filed region ② the different attenuation rates of incidents due to different traveing distances ③ the non-uniform wave field distribution characteristics induced by metro;the factor ① and ② act on shear wave components to affect the position of the MAR;the factor ③ acts on both shear and longitudinal waves;the more the shear wave components than the longitudinal ones,the more remarkable the MAR phenomenon.%地铁运行引发的地表竖向振动并非单调递减,存在局部放大现象.对上海3处典型的埋置地铁行经场地进行了地表振动实测,实测结果表明,各场地地表振动的衰减曲线均存在局部放大区,第一局部放大区(主放大区)最为显著,位于1倍埋深的振中距(地表与振源投影点距离)附近.基于弹性波场理论,辅以有限元数值模拟,分析主放大区的主要影响因素有:①近场体波在地表入射与反射的叠加效应;②入射波在场地内的行程差导致的衰减率不同;③地铁运行引发的场地弹性波场不均匀分布特征.因素①和因素②主要作用于剪切波分量以影响主放大区的出现位置,因素③对纵波和剪切波均有较大影响,入射波场的剪切波分量较纵波分量越占优,主放大区现象就越显著.
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