A simple definition of the duration of strong earthquake ground motion based on the mean-square integral of motion has been presented. It is closely related to that part of the strong motion which contributes significantly to the seismic energy as recorded at a point and to the related spectral amplitudes. Correlations have been established between the duration of strong-motion acceleration, velocity, and displacement and Modified Mercalli intensity, earthquake magnitude, the type of recording site geology, and epicentral distance. Simple relations have been presented that predict the average trend of the duration and other related parameters as a function of Modified Mercalli intensity, earthquake magnitude, site geology and epicentral distance
