考虑近断层方向性效应及土层非线性影响的场地概率危险性分析

Probability Seismic Hazard Analysis Considering the Near-fault Directivity Effect and Nonlinear Site Response

摘要:

针对一典型砂土场地基于等效线性分析方法，研究了土层对输入近断层地震动脉冲特性的影响。选取两组近断层脉冲和非脉冲地震动对地表加速度反应谱放大系数进行了对比研究。结果表明：基岩非脉冲地震动经过土层的高频滤波作用传至地表后有转换成脉冲地震动的可能；基岩脉冲地震动经土层传播至地表后仍具有脉冲特性，部分含有潜在第二脉冲的地震动由于共振作用会产生附加脉冲。与非脉冲地震动相比，脉冲地震动会引起土层较强的非线性响应，导致加速度反应谱放大系数随基岩加速度值的增大衰减较快；而对于长周期加速度反应谱（3 s），脉冲地震动引起的放大系数在基岩加速度大于0.1 g时远大于非脉冲地震动引起的放大系数。最后通过回归分析得到场地放大系数方程，建立了一种考虑近断层脉冲特性及土层非线性相互影响的场地概率地震危险性分析方法。

Abstract:

This paper presents seismic response analyses，based on the equivalent linear method，of a sandy site subjected to near-fault ground motions.We investigate the effects of soil nonlinearity on the pulse characteristics of input ground motions，and explore the amplification factors for the spectral acceleration from near-fault pulse like and non-pulse-like motions. We found that input non-pulse motions can be transformed into pulse-like motions by attenuating the high-frequency component as it propagates through the soil.The input pulse motion probably remains as a pulse characteristic，and tends to have multiple pulses when the input motion includes other potential pulses.The attenuation of the amplification factor, along with the spectral acceleration of the bedrock motion，has a more significant effect on pulse-like motions than non-pulse motions.We expect that this finding is related to the strong nonlinear response of the soil caused by the pulse excitation.However，the amplification factor for a long period（e.g., 3 s），when the pulse motion is greater than 0.1 g，is larger than that of a non-pulse motion.Finally，a probabilistic seismic hazard analysis （PSHA）procedure is proposed to incorporate the coupled effects of the near-fault pulse characteristic and the nonlinearity site response.