Exploring the characteristics of strong earthquake ground motions is a very important research topic to both the seismological and engineering communities for a long period [1-2].Since 1947 when the white noise model of earthquake ground motions was firstly established by Housner [1].the earthquake motions have been generally viewed as stochastic processes in the earthquake engineering community.Furthermore, the random vibration analysis of seismic responses of structures has been widely implemented.Undoubtedly, it is reasonable to certain degree that the aggregation of ground motion samples is regarded as a random process for the convenience of probabilistic analysis of structural seismic responses.