2009 Volume 65 Issue 1 Pages 38-51
The purpose of this paper is to compare spectral characteristics of strong ground motions and microtremors using records obtained at 20 sites of an array observation system. The array observation system is situated in Sendai City, Japan. Using the motion records observed by the system, the authors estimated statistically spectral amplification factors at each observation site. These spectral amplification factors of strong ground motions are quite different depending on the local soil condition of each site. Microtremors were also observed at all the observation sites. The so-called H/V spectra, which are the spectral ratio of the horizontal component to the vertical one, were obtained from the microtremors. Comparisons between the statistical amplification factors of strong motions and H/V spectra of microtremors showed that they have strong similarity in spectral shape. Although such highly similar shape of spectra was found between the strong motions and microtremors, the absolute spectral amplitudes in both indicated a difference in level, revealing some remarkable offsets of spectral amplitude that are independent of period. Based on the comparisons, fitting analyses between the spectral amplification factors and H/V spectra of microtremors were made to obtain an optimal parameter of offset for the H/V spectra of microtremors. This paper finally concludes that microtremors are useful to obtain amplification factors due to local soil conditions with aid of an offset method of their H/V spectra.
Proceedings of the JSCE Earthquake Engineering Symposium
Environmental systems research
