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We have derived equations for predicting the larger horizontal and the random horizontal component of peak acceleration and of 2-, 5-, 10-, and 20-percent-damped pseudovelocity response spectra for 46 periods ranging from 0.1 to 2.0 sec. The equations were obtained by fitting a functional form to empirical data using a two-stage regression method. 271 two-component recordings from 20 earthquakes were used to develop the equations for peak acceleration, and 112 two-component recordings from 14 earthquakes were used for the response spectral equations. The data included a subset of those used in earlier studies by us (Joyner and Boore, 1981, 1982), augmented by data from three recent earthquakes with magnitudes close to 7: 1989 Loma Prieta, 1992 Petrolia, and 1992 Landers. Besides the addition of new data, this study differs from our previous work in several ways: records at distances equal to and greater than the distance to the first record triggered by the 5 wave were not included (this resulted in eliminating 56 records from our previous data set for peak horizontal acceleration and 19 records from our previous data set for response spectra; in addition, 7 records providing peak acceleration values were removed for a variety of other reasons), we used weighted regression in the second stage of the twostage regression, equations were evaluated at many more periods than previously and for four values of damping, and the smoothing of the regression coefficients over period was done by computer rather than by eye. In addition, we changed the way in which geologic conditions beneath the site are classified. Our previous studies used a binary rock/soil classification. In anticipation of future building code classifications, we now divide site geology into four classes, depending on the average shear-wave velocity in the upper 30m.
Boore et al. (1993) studied this question.