An orthogonal set of principal axes is defined for earthquake ground motions along which the component variances have maximum, minimum and intermediate values and the covariances equal zero. Corresponding axes are defined which yield maximum values for the covariances. The orthogonal transformations involved are identical in form to those used in the transformation of stress. Examination of real accelerograms reveals that the major principal axis points in the general direction of the epicentre and the minor principal axis is nearly vertical. It is concluded that artificially generated components of ground motion need not be correlated statistically provided they are directed along a set of principal axes.

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Yutaka YAMAZAKI*, Members of A.I.J. SYNOPSIS This paper is an app]ication of the random vibration theory in earthquake engineering, frem which a general analytical method is developed for the response of a multi-story building with a linear stable system subjected to earthquake excitation. This analytical method is applied to evaluate the response of a three story building subjectecl to an accelerometer recording of the Tokachi-Oki earthquake. Expected maximum story displacements ancl expected number ef cyc!es with varying lntensities of the repeated story shearing forces due to the strong ground motion are computed and compared with the corresponding values obtained by a deterministic analysis method. Hence, a dynamic response prediction method for the expected intensity of future earthquakes is here by discussed.

TwQ typical methods ， so − called ' static design ' and ' dynamic design ' ， are conventionally used for estimating seismic load of structures in civil eng 三 neering 、 In this paper a new method for earthquake resistant design is proposed ． The method is an approach to estimate a structural res − ． ponse due to a ground motion by using of a simple formu 且 a derlved from a multiple regression analysis ． To confirm validity of the method ， seismic loads working on basements of an embedded structure are examined