抄録
An aim of this paper is to obtain fundamental information for understanding the varied and complex shape of Fourier amplitude spectrum of the earthquake motion wave. Fourier amplitude spectrum of the earthquake motion wave can be simulated by the superposition of a class of Fourier transforms, because an earthquake motion wave can be regarded as consisting of the successively reached element waves. To achive the object of this paper, a variety of Fourier amplitude spectra were calculated analytically according to idealized patterns of superposition of a class of Fourier transforms (Tables 1〜3). Through the examination of the shape of the calculated Fourier amplitude spectra showed in Figs.1〜3, the following general properties were abstracted. ・Fourier amplitude spectrum of a time function consisting of element waves with time lag, has a fluctuating shape along the frequency band common to the element waves. The degree of fluctuation is related to the randomness of the time lag, and the case of the time lag being random has less fluctuating shape of the Fourier amplitude spectrum than the case of constant time lag. ・The shape of Fourier amplitude spectrum of a time function, which consists of element waves having the mutually identical shape of the amplitude spectrum and common frequency band, is not almost affected by the randomness with respect to weight of the amplitude value.
