近断层地震动的频谱周期参数和非平稳特征分析

Analysis of frequency content parameters and non-stationary characteristic of near-fault ground motions

分析地震动的频谱周期参数和频率非平稳特征,是地震危险性分析和结构抗震设计的重要内容。本文对近断层地震动记录按照不同的运动特征分组,进行了Hilbert-Huang变换分析。结合相关的定义得到了表征地震动频谱特性的7个周期参数,包括:Fourier幅值谱平均周期Tm、Hilbert边际谱平均周期Tmh、特征周期Tc、卓越周期等,并计算了地震动的Hilbert谱瞬时频率时程变异系数。计算结果表明,从整体上把握地震动频谱特性的三个周期参数Tm、Tmh和Tc适合于表征近断层地震动的频谱成份。近断层地震动的频率非平稳特征显著,Hilbert谱瞬时频率变异系数良好地反映了地震动的频率非平稳性质和程度。而且,考察了近断层地震动运动特征对地震动频谱周期参数和频率非平稳性的影响。

Analyzing the frequency content parameters and non-stationary property of earthquake ground motions is an important topic of seismic hazard assessment and structural seismic design. The near-fault ground motion recordings are divided into several groups according to their motion characteristics. Hilbert-Huang transform is implemented for these ground motions. Then, seven frequency content parameters of ground motions are obtained including the mean period of Fourier amplitude spectra Tm, mean period of Hilbert marginal spectra Tmh, characteristic period Tc and predominant periods and so on according to the related definitions. Furthermore, the variance coefficients of instantaneous frequency time histories of Hilbert spectra are calculated. Numerical results indicate that three period parameters Tm, Tmh and T are suitable for characterizing the frequency content of near-fault ground motions. The non-stationary characteristic of frequency content of near - fault ground motions is remarkable, and the variance coefficients of instantaneous frequency of Hilbert spectra can reflect well the non-stationary property and degree of ground motions. Moreover, the influence of motion characteristics of near-fauh ground motions on their frequency content parameters and nonstationarity is examined.