A Statistical Model for Estimating Response Spectra of Strong Earthquake Ground Motions with Emphasis on Local Soil Conditions

Abstract

Response spectra of strong earthquake ground motions have been known to be influenced by many factors-source mechanism, propagation path of earthquake waves and local soil conditions. In order to clarify the effects of these factors on response spectra, the present paper deals with a statistical analysis of the response spectra of strong-motion earthquake records obtained in Japan. A new multiple regression technique, in which not only the earthquake factors but also the local site conditions are employed as its independent variables, is carried out and an empirical expression for scaling the response spectra is derived. In addition to scaling the response spectra on the bed rock in terms of earthquake magnitude, hypocentral depth and epicentral distance, the effects of the local site conditions on the response spectra are estimated quantitatively as amplification factors of spectra. It is shown that the amplification factors of spectra depend significantly on the local soil layer conditions, and they agree comparatively well with the theoretical amplification factors to the vertical indicence of S-wave. Also, the statistical model presented here is confirmed to be an effective tool for predicting response spectra provided that earthquake factors and site soil conditions are available.