基于地震动反应谱与傅里叶谱确定场地卓越频率的差异性

Difference Analysis of Site Dominant Frequencies Obtained from Response Spectra and Fourier Spectra of Earthquake Motion

强震动记录的HVSR法常用于评估场地卓越频率,计算强震动记录HVSR时常采用加速度反应谱或加速度傅里叶谱,但两者会给出不同的评估值。为揭示反应谱比和傅里叶谱比评估场地卓越频率的差异,本文选取日本KiK-net台网中场地条件可近似为一维场地模型的16个台站,以其获取的强震动记录开展场地卓越频率研究。首先提出了评估场地卓越频率的数据处理方法,主要包括S波截取、Taper预处理、基于高斯拟合的自动寻峰。探讨并给出了阻尼比、平滑的带宽系数取值对场地卓越频率评估的影响规律;对反应谱阻尼比取10%,对傅里叶谱平滑的带宽系数取20~40之间获取的场地卓越频率较为准确。然后对比分析了利用地震动加速度反应谱比和傅里叶谱比得到的场地卓越频率与场地土层模型计算得到的基于传递函数的自振频率。研究结果表明,对大多数台站而言,采用傅里叶谱比计算场地卓越频率具有明显的优势,对于Ⅱ、Ⅲ、Ⅳ类场地上的台站均有如此结论,只有对少数特定台站,采用反应谱比方法效果更好。

The Horizontal-to-Vertical Spectral Ratio(HVSR)method for strong motion records is commonly used to evaluate a site’s predominant frequency.Both the acceleration response spectrum and the acceleration Fourier spectrum are frequently employed to calculate the HVSR of strong motion records,but these two approaches often yield different results.To investigate the differences in predominant site frequency between the response spectrum ratio and the Fourier spectrum ratio,this study analyzes 16 stations from Japan’s KiK-net network,where site conditions can be approximated using a one-dimensional site model.First,data processing methods for evaluating site predominant frequency were developed.These include S-wave interception,taper preprocessing,and automatic peak identification based on Gaussian fitting.The effects of damping ratio and smoothed bandwidth ratio on site frequency evaluation were examined.It was found that using a 10%damping ratio for the response spectrum and a smoothing bandwidth ratio of 20~40 for the Fourier spectrum yielded more accurate results.Next,the predominant site frequencies obtained from the ground motion acceleration response spectrum and Fourier spectrum were compared with the natural frequency calculated from the site soil model using the trans-fer function.The results indicate that the Fourier spectrum ratio provides a more accurate estimate of the predominant site frequency compared to the response spectrum ratio for most stations,particularly those located on Class II,III,and IV sites.However,a few specific stations showed better results when using the response spectrum method.