基于二维数值模拟的盆地地震动放大系数

Basin amplification effect of seismic ground motion based on seismic wave numerical simulation in two-dimensional model

盆地地震效应的研究已取得长足进展,但是地震动盆地放大效应与盆地特征参数之间的定量分析还尚不充分。文中利用盆地宽度、沉积层厚度、盆地边缘倾角和阻尼比等特征参数的不同组合建立的84个精细化二维盆地有限元模型,基于波动有限元数值模拟方法结合强震动观测记录定量评估了地震动盆地放大效应。结果表明:(1)地震动盆地放大效应明显依赖于周期和盆地内的位置;(2)地震动盆地放大效应主要集中于不超过1.4 T_(0)(场地自振周期T_(0))的周期范围内;(3)盆地边缘局部区域的地震动放大系数小于1.0,这可能与盆地边缘入射地震波(SV波)的折射导致部分体波向盆地内传播以及部分SV波转化为沿垂直分量传播的P波等有关;(4)T_(0)<3.0 s时盆地边缘放大效应最明显,放大系数为1.10-1.40,T_(0)≥3.0 s时盆地中部放大效应最明显,放大系数为1.30-1.79;(5)不考虑盆地内位置对地震动放大效应的影响时,盆地全局放大系数可取1.38-1.86,该放大系数高于我国现行《建筑抗震设计规范》中规定的不利地段地震影响系数的增大系数1.1-1.6。

Great progresses in researches on basin seismic effect are still not enough to shield the deficiencies in revealing the quantitative relation between basin amplification effect of seismic ground motion and basin characteristic parameters.In this study,84 two-dimensional fine finite-element basin models are first established according to various combinations among the basin width,basin sedimentary thickness,sloping angle of basin edge,damping ratio of basin deposit sediment.The finite-element simulations of seismic wave in these basin models are further performed to quantitatively evaluate the basin amplification effect of seismic ground motion.Results indicate the following findings.(1)Basin amplification effect is significant dependent on the period and location in basin.(2)The basin amplification effect is mainly limited in the period ranges not greater than 1.4 T_(0)(T_(0),site fundamental period).(3)The amplification is generally lower than 1.0 at some regions of basin edge,which may be ascribed to the propagation of the body wave to the basin interior and the conversion of SV to P wave due to the refraction of the incident seismic wave on the basin edge.(4)The strongest amplification(1.10-1.40)occurs at the basin edge for basin with T_(0)<3.0 s,while the strongest amplification(1.38-1.86)occurs at the basin center for basin with T_(0)≥3.0 s.(5)The basin amplifications are mainly in the range of 1.38-1.86 without considering the influence of location in basin,which is larger than the coefficient 1.1-1.6 for amplifying the seismic effect coefficient at unfavorable site in the code for seismic design of buildings in China.