In probabilistic seismic hazard analysis, severer ground motions than those used in usual design is very important to estimate a damage frequency of structures and components. An artificial ground motion of such a severer earthquake is required to have nonlinear response spectral properties similar to those of real motions. In this paper we propose a new simple non-parametric method to generate an artificial earthquake motion which has a target response spectrum. In this method, the artificial earthquake motion is generated in the form of the orthogonal wavelet expansion, in which the wavelet coefficients of the artificial earthquake motion are given by weighted sums of wavelet coefficients of observed earthquake motions in each frequency range. The weights of observed earthquakes are adjusted to reduce the difference between the response spectrum of the artificial earthquake motion and the target response spectrum, to a tolerance level. We apply this method to generate an artificial earthquake motion subject to the Ohsaki spectrum, from randomly selected 20 observed motions in a given range of hypocentral distance. Each of these 20 observed motions is found to contribute appreciably to the generated motion in all frequency ranges. The average and standard deviation of group delay time of the generated motion are, respectively, nearly at the central values of those for the observed motions. These results show that the artificial earthquake motions have average time-frequency characteristics of those for the observed motions.
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