# Arias Intensity

The Arias Intensity (IA) 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 Td 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]

## References

1. ^ "New predictive equations for Arias intensity from crustal earthquakes in New Zea" (PDF). Journal of Seismology. 13 (1): 31–52. Bibcode:2009JSeis..13...31S. doi:10.1007/s10950-008-9114-2.
2. ^ a b "7. Seismic landslide hazard zonation". Faculty of Geo-Information Science and Earth Observation of the University of Twente. 2006-09-29. Archived from the original on 2010-08-15. Retrieved 2010-12-12.
3. ^ Wolfgang A. Lenhardt (2007). "Earthquake-Triggered Landslides in Austria – Dobratsch Revisited" (PDF). Jahrbuch der Geologischen Bundesanstalt. Archived from the original (PDF) on 2011-05-31.