Abstract
The amplitude characteristics as the fundamental natures of microtremors was discussed at the present paper. The experimental field is Hakodate City in Hokkaido.
The random physical phenomena of microtremors were treated as the stationary random process. In order to express the amplitude characteristics of microtremors, power spectral density functions were therefore computed. The statistical check of the amplitudes microtremors was used by means of χ2-test.
Theoretical amplitude characteristics from the underground structure is the frequency of the minimum group velocity of L0- and M11-wave and the amplitude ratio by the theory of multiple reflection. They were compared with the predominant frequencies of power spectral density functions of microtremors.
From the point of view to remark only the predominant frequency at the amplitude characteristics of microtremor, we may conclude from these comparisons that the horizontal component of microtremors can be treated as the amplitude characteristics of the amplitude ratio from S-wave structure or the fundamental mode of Love wave at the places where the boundary of the subsoil and basement is district. However, the amplitude characteristics of the vertical component of microtermor never agrees with the amplitude ratio from P-wave structure, and it agrees or not with the amplitude characteristics of the fundamental mode of Rayleigh wave.
Furthermore, the spectra of waveform by explosion seismic observation was compared with the amplitude characteristics from the theory of multiple reflection, the minimum group velocity of surface wave and the power spectra of microtremor.
