美国加州Ridgecrest地震的地震动特性分析

Analysis on Seismic Motion Characteristics of the Ridgecrest Earthquakes in California USA

为研究同一地震序列中两场震源相近,发震时间间隔较短的主要地震活动中获取的地震动时频特性的异同,选取了2019年7月美国加州Ridgecrest地震序列中震级分别为MW 6.4和MW7.1的两场地震,对比研究了两次地震中地震动参数随着震中距的衰减趋势,并与俞言祥模型进行了对比;讨论了这两个相近事件中地震动三要素(峰值加速度、反应谱和持时)的异同,重点分析了两条不利地震动的反应谱;通过希尔伯特-黄变换(HHT)获得地震动的HHT谱,分析了地震动能量在时间和频率成分上的分布特征.结果表明:大部分地震动参数的衰减趋势与俞言祥模型吻合较好;两场地震的反应谱基本相似;地震动HHT谱最大能量所对应的瞬时频率和地震动时程峰值加速度所在循环的峰-谷频率很接近;两次大地震相继发生可能会对结构造成更大的损坏.

In order to figure out the different temporal and spectral characteristics between two earthquakes with close hypocenter and short time interval in the same seismic sequence,two main shocks,MW 6.4 and MW 7.1 among the 2019 Ridgecrest earthquakes at California USA in July are selected.The attenuation trend of ground motions parameters with the change of epicentral distance for these two earthquakes is compared with Yu's model.The difference of three key elements of ground motions between these two earthquakes,including peak ground acceleration,response spectrum and duration,are analyzed.The potential seismic damage to structures is discussed by the response spectrum analysis of the selected two severest ground motions.The Hilbert-Huang transform(HHT)is adopted to obtain the HHT spectrum of ground motions for identifying the energy distribution in temporal and spectral domains.It shows that the attenuation trend of most of data agrees with Yu’s model.The response spectra of the two earthquake events are similar.The instantaneous frequency corresponding to the largest energy of HHT spectrum is close to peak-trough frequency corresponding to the time series cycle with peak ground acceleration.Structures may be severely damaged subjected to two earthquakes occurred successively.