Abstract
We often face the large scattering of peak accelerations in the statistical analyses of strong ground motion. The ratios of source spectra were evaluated from the acceleration records observed at the same stations for some earthquake pairs whose epicenters were very close so as to cancel the effects of a path and a site. The stress drops of these events were estimated by comparing the observed source spectral ratios and theoretical ones. The stress-drop affects the short period spectral levels. It is effective for reducing the variance of estimated peak accelerations of ground motions to consider the difference of stress drop in the attenuation relations.
