Arias Intensity

A ground-motion parameter derived from an accelerogram and proportional to the integral of the acceleration squared over the entire signal duration.

Introducing the function of motion intensity:

where a(t) is the acceleration at time t and g the gravity acceleration, the Arias Intensity is the maximum value of this function, i.e.:

I_A = I(T_d)

where T_d is the accelerogram total duration

Arias Intensity is dimensionally a velocity [cm/s]

A sample of calculation of the Arias Intensity is shown in the figure (see Duration)