観測地震波形を利用した模擬地震動の作成

Abstract

In probabilistic seismic hazard analysis, severer earthquake motions than those used in usual design is very important to estimate a damage frequency of structures and components. An artificial earthquake 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 convenient non-parametric method to generate an artificial earthquake motion which conforms to a target response spectrum. In this method, the artificial earthquake motion is generated in the form of the orthonormal wavelet transform, 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 band. The weights for observed earthquake motions 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 several observed earthquake motions in a given band of magnitude and epicentral distance. Each of these several observed earthquake motions is found to contribute appreciably to the generated motion in all frequency bands. The average and standard deviation of group delay time of the generated motions are, respectively, nearly at the central values of those for these observed earthquake motions. These results show that the artificial earthquake motions have average time-frequency characteristics of those for the observed earthquake motions.