基于小波变换的地震动时-频特性研究

对美国NGA,采用一维连续小波变换得到每条记录的小波功率谱。研究了任意时间处小波功率谱最大值所对应的主频率。结果表明:地震动主频率随时间的增大逐渐减小;竖向地震动分量的主频比水平向分量随时间减小更快。分别采用线性函数模型、指数函数模型和指数三角函数模型,分析了场地、震级和震中距对主频变化曲线的影响,拟合了主频率在不同场地条件、震级、震中距等情况下随时间的变化曲线,水平向和竖向的频率时变曲线整体上都是随时间递减的,且竖向衰减得更快些,大多数情况下竖向记录的高频成分比水平向记录的相应成分要多。

Time-Frequency Characteristics of Ground Motions Based on a Wavelet Transform

3 551 sets of earthquake records from the NGA database of America were grouped according to site conditions, moment magnitude, and epicentral distance.The wavelet power spectrum of each record was calculated using a one-dimensional continuous wavelet transform.The predominant frequency corresponding to the maximum value of the wavelet power spectrum at every time was investigated.Results showed that the predominant frequency of ground motion gradually decreased with time, and the time-variation of the predominant frequency of the vertical component seemed more remarkable than that of the horizontal component.Furthermore, a linear function model, together with an exponential model and an exponential trigonometric model, were used to fit the time-varying curves of predominant frequency under varying magnitudes.Epicentral distance, effects of site conditions, moment magnitude, and epicentral distance on the time-varying curves of predominant frequency were analyzed.Time-varying curves of horizontal and vertical frequencies decreased with time and decayed more quickly in the vertical direction.In most cases, the high-frequency components were higher in the vertical records than those in the horizontal records.