The 1999 Chi-Chi

Taiwan

China earthquake （Mw = 7. 6） supplied us unprecedented recordings of near fault round motions and made it possible to study the randomness of near fault ground motions. In this paper

the acceleration history of every component is regarded as a random process. The recordings of 30 near-fault stations with certain qualification are used as assembly of the three random processes respectively. The autocorrelation and cross-correlation matrixes of assembly and correlation function of sample functions are studied. We find that the correlation matrixes of acceleration random process comprise a random component. Such kind of correlation could not be simulated by deterministic mathematical expression. Then the correlation function of the stationarized sample functions of acceleration random process is studied. We found that its autocorrelation function is still a random process

which could be divided into two parts

a deterministic process and a random process. A mathematic model of the autocorrelation function is constructed in this article. Considering the high randomness of the correlation-functions of near fault accelerations

the strong earthquake near fault ground motion is named as the super random process in this article. To study the random characteristics of acceleration time history

the autocorrelation function of cross-correlation function of three components are studied at the end of this paper.