Abstract
Microseisms observed on soil deposite in the Nohbi plain, are likely to contain both source properties of sea waves and natural vibration of soil layers. Therefore, it is indispensable to distinct these two characteristics for applying the microseisms to engineering use. The propagation of microseismic waves is observed by a tripartite method in four sites with quite different layer thickness of deposits on a base rock. A wave analysis of observed record is carried out by a cross correlation method, and spectral structure, dispersion properties and wave types are discussed from the wave propagation view point. Important results obtained are as follows. 1. Typical spectral pattern is of two-peaked form under the frequency of 1.0 Hz. 2. Predominant frequency peak in lower range is different in each site and has not any considerable propagating characteristics. 3. Peak of higher frequency shows the remarkable properties of the propagation in three sites on soil deposits. 4. It is concluded that the lower one corresponds the thickness of deeper deposits in the plain and the higher one seems to be dependent on the source properties of sea waves.
