A. Fallahi - PhD student, Graduate School of Natural Science and Technology, Kanazawa
M. Kitaura - Professor, Department of Civil Engineering, Kanazawa University,
M. Miyajima - Professor, Department of Civil Engineering, Kanazawa University,

Using records of the 1995 Kobe-Japan and the 1978 Tabas-Iran earthquakes, both with peak ground accelerations (PGA) of more than 800 cm/s2, hereinafter referred to as target records, the aim of this study is to make critical earthquakes by a probabilistic method that show similar amplitude and frequency characteristics as targets but cause greater structural response than that of them. The critical earthquake is smooth assembling of artificial waves generated from modified power spectral density (PSD) graphs of target at consecutive time intervals. The PSD graph is modified by amplifying the PSD graph of target at each time interval in a specified width and reducing it in the other parts in which the areas under the PSD-frequency diagrams in original and modified ones to be same. Because of using probabilistic method, we have to check whether or not each made critical earthquake induces larger response than that of the target.By applying the method to two SDOF nonlinear structures, for each Kobe and Tabas records at each structure 20 and totally 80 critical earthquakes are made, and the most critical ones showing much larger structural response than that of the targets while having similar characteristics to them are introduced