Strong-motion duration and RMS amplitude of earthquake records

abstract A simple procedure is proposed for estimating the strong-motion duration s o and the rms strong-motion acceleration tσ o of earthquake ground motion records. The strong-motion duration is found to be nearly proportional to the quantity I o / a 2 max where a max is the maximum ground acceleration, and I o is the integral over time of the squared accelerations. A less important factor influencing the relationship between s o and I o / a 2 max is the predominant period T o of the strong phase of the accelerogram. The following simplified expression is also derived for the strong-motion duration: s o = 7.5 I o / a 2 max . Duration-related statistics are presented for a set of 140 horizontal components of earthquake ground motion recorded in California. The dependence of duration upon magnitude, epicentral distance, and local condition is examined. The proposed measure of duration provides an important link between the major spectral representations of earthquake ground motion: the Fourier amplitude of acceleration, the acceleration spectral density function, and the response spectrum.