Simplified frequency content estimates of earthquake ground motions

It is often useful in earthquake engineering practice to characterize the frequency content of an earthquake ground motion with a single parameter. Three simplified frequency content parameters are examined: mean period (T-m), predominant period (T-p), and the smoothed spectral predominant period (T-o). These frequency content parameters are calculated for 306 strong motion recordings from 20 earthquakes in active plate-margin regions. These data are used to develop a model that describes the magnitude, distance, and site dependence of these frequency content parameters, Nonlinear regression analyses are performed to evaluate model coefficients and standard error terms. The results indicate that the traditional T-p parameter has the largest uncertainty in its prediction, and that previous relationships proposed to predict T-p are inconsistent with the current data set. Moreover, T-m is judged to be the best simplified frequency content characterization parameter, and it can be reliably estimated.