随机模型上的地震动模拟研究

Simulation of Seismic Ground Motion on Random Models

介绍了一项随机模拟实验,该实验通过模拟一个具体场址模型的地震动响应了解模型参数不确定性对模拟结果的影响。首先给定一个典型的第四纪沉积层场址模型的参数(包括地层厚度、介质密度、横波速度和品质因子等)的统计特征,并据此在计算机上按截尾的正态分布随机抽样形成了16384个随机模型,然后分别在各个模型上进行SH波地震动响应模拟,最后对所有的模拟结果进行统计分析,了解模型参数的不确定程度与模拟结果变化范围之间的关系。实验结果表明,模型参数不确定性对模拟结果的影响程度是随频率增大的。随机模型地震动响应的第一个放大峰发生在353±031Hz的频率上,其幅值为438±076;第二放大峰发生在885±108Hz的频率上,幅值为422±090。两放大峰值的均方差与均值之比分别为18%和25%。与模型参数20%的相对变化程度大致相当。但更高频率上振幅响应的均方差与均值之比则高达30%～40%。

In this paper we introduce an experiment which was performed to study the effects of uncertainties of model parameters on seismic ground motion modeling results. First, the statistic characteristics of the parameters, including layer thickness, density, shear wave velocity and quality factor Q, were given to an indicative Quaternary site model for the study. Then ~16?384 random models were generated according to the given parameter characteristics. On each of these random models SH wave propagation was simulated to determine the seismic ground motion on the surface of the model. Finally the statistics was performed on the modeling results to reveal the correlation between the variation of the modeling results and the uncertainties of the model parameters. It was found that the effect of the model parameter uncertainties on the modeling results was getting more significant as frequencies increase. The fundamental ground motion peaks of the models are found at 3.53±~0.31?Hz , with amplitudes of 4.38±~0.76?Hz . The secondary peaks are found at 8.85±~1.08?Hz , with amplitudes of 4.22±0.90. The relative variation of the peak amplitude, defined as the ratio of the standard deviation to the mean, are about 18% and 25% for the fundamental and secondary peak amplitudes, respectively. The variation is in the same extent of the variation for the model parameters (20%). However, the standard deviations of amplitude responses at frequencies higher than the secondary peaks are found to be as much as 30% to 40% of the means.