The Arias Intensity is a measure of the strength of a ground motion

Strong ground motion

"Peak ground velocity" redirects here.Seismologists usually define strong ground motion as the strong earthquake shaking that occurs close to a causative fault...

. It determines the intensity of shaking by measuring the acceleration of transient seismic wave

Seismic wave

Seismic waves are waves of energy that travel through the earth, and are a result of an earthquake, explosion, or a volcano that imparts low-frequency acoustic energy. Many other natural and anthropogenic sources create low amplitude waves commonly referred to as ambient vibrations. Seismic waves...

s. It has been found to be a fairly reliable parameter to describe earthquake shaking necessary to trigger landslides. It was proposed by Chilean engineer Arturo Arias in 1970.

It is defined as the time-integral

Integral

Integration is an important concept in mathematics and, together with its inverse, differentiation, is one of the two main operations in calculus...

 of the square of the ground acceleration:

(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.

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