Abstract
In the application of the reliability-based design, such as, load and resistance factor design, it should be necessary to predict the variance of the exected maxima of the seismic ground motion for a given return period. In this paper, we deal with the seismic model which is derived from three fundamental assumptions; (1) the occurrences of great earthquakes follow a Poisson process, (2) the cummulative distribution of magnitude is based on the Gutenberg-Richter's law, and (3) the intensity of the ground motion is determined by the attenuation curve. Using the extreme value distribution and the standard error of the i-th largest value derived from this model, the coefficient of variation, V_γ(t), of the expected maxima against return period, t, is estimated. The following conclusions are drawn from the results. (1) For smaller return period, say, 20-year, V_γ(t) is proportional to the coefficient b_2 of the attenuation-curve in equation 1. (2) V_γ(t) decreases in proportion to log(t). (3) The variance of V_γ(t) in several sites is small. (4) V_γ(t) for a 100-year return period are nearly 0.52 in displacement, 0.41 in velocity and 0.38 in acceleration, respectively.
