Abstract
　The feature of ground shaking owing to the Loma Prieta, l989 Earthquake is summarized. Attenuation of maximum accelerations observed on the ground was classified into four groups based on the geological conditions of observation points. A ground motion amplification factor for each classification of geological condition is derived by comparing observed acceleration and theoretically calculated maximum acceleration at bed rock level. This supports the opinion of seismologists studying aftershokcs that soil conditions and resulting ground motion amplification were main reasons in the failure of structures.
　A simplified analytical procedure that takes into account the fault extent and rupture process was used to estimate the attenuation of peak ground motion. The estimated distribution of ground motion intensity was compared with observed data. Estimated peak acceleration near the fault region exceeds 400 gals and its distribution shows good agreement with the observed one.

【キーワード】：ロマプリエタ地震，地盤震動，アテニュエーション，最大加速度

*京都大学防災研究所
Disaster Prevention Research Institute, Kyoto University