Arias intensity

The Arias intensity (I_A) is a measure of the strength of a ground motion.¹ It determines the intensity of shaking by measuring the acceleration of transient seismic waves. It has been found to be a fairly reliable parameter to describe earthquake shaking necessary to trigger landslides.² It was proposed by Chilean engineer Arturo Arias in 1970.

It is defined as the time-integral of the square of the ground acceleration:

${\displaystyle I_{A}={\frac {\pi }{2g}}\int _{0}^{T_{d}}a(t)^{2}dt}$ (m/s)

where g is the acceleration due to gravity and T_d is the duration of signal above threshold. Theoretically the integral should be infinite.³

The Arias Intensity could also alternatively be defined as the sum of all the squared acceleration values from seismic strong motion records.²