An inversion method to separate effects of source, propagation path, and local site from S-wave spectra is applied to earthquake observation data obtained in the southwestern Kanto plain, Japan. First, effects of building in which seismometer is installed are evaluated from spectral ratio of microtremor records that were simultaneously obtained in the building and at the free surface in its vicinity for correcting the S-wave spectra. Theoretically calculated amplification factor due to shallow weathered layers and the spectral ratio of microtremors at a rock site are used as a constraint condition in our inversion. Estimated source spectra show a ω^-2 decay with increasing frequency. Q_s-value along the propagation path in the Earth's crust is in an agreement with results of previous studies. Strong site-dependency was found in the separated site amplification factors. In particular, soft soil site has an amplitude decrease in frequencies higher than 2Hz. The amplification factors were well explained by theoretical amplifications of reverberating S-waves in subsurface structural models from geophysical surveys. These results suggest the appropriateness of the constraint condition used in our inversion.

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