Duration

Duration is defined as the time interval of the accelerometric signal in which the seismic motion is significant.

To this aim two definitions are often used:

- duration based on the exceedance of a threshold value (bracketed duration): a threshold is fixed, typically 0.05g, above which it is deemed that the motion has relevance for engineering purposes; the duration is the time interval between the first and the last exceedance of this value;

- duration based on the motion intensity: The Arias Intensity function I(t) is calculated (see Arias Intensity), and normalized with respect to its maximum value I_max; the duration corresponds to the time interval t₂-t₁, where I(t₁) = 0.05 and I(t₂) = 0.95.

In ITACA the seismic motion duration is calculated on the base of the Arias Intensity.