Abstract
In order to discuss the relationship between the lower and higher frequency components of source spectra, we deal with impulse train model as source time function, because spectral characteristics of source time function depend on occurrence times of impulse function which corresponds to small extent on the fault. Considering the successive rupture of small extent on a fault plane, we represent the source time function by time series which consist of random sequence of impulses. Under this assumption, the spectral characteristics of source time function are obtained analytically and numerically from the stochastic viewpoints: namely, on one hand, the trend of impulse train determines the frequency characteristics of phase spectrum in lower frequency range, and on the other hand, the fluctuation from the trend settles higher frequency range. Furthermore, it is shown that the spectral properties of source time function can be determined using only two parameters which are number of impulses N and probability density function (PDF) of occurrence time of impulse fT(t).
