Arias intensity

The Arias intensity (I_A) is a measure of the strength of a ground motion.{{cite journal|title=New predictive equations for Arias intensity from crustal earthquakes in New Zea |journal=Journal of Seismology| volume =13| issue= 1|pages=31–52 |bibcode=2009JSeis..13...31S |doi=10.1007/s10950-008-9114-2|url=https://hal.archives-ouvertes.fr/hal-00478434/file/PEER_stage2_10.1007%252Fs10950-008-9114-2.pdf}} 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.{{cite web |url=http://www.itc.nl/ilwis/applications/application07.asp |title=7. Seismic landslide hazard zonation |publisher=Faculty of Geo-Information Science and Earth Observation of the University of Twente |date=2006-09-29 |access-date=2010-12-12 |archive-url=https://web.archive.org/web/20100815092518/http://www.itc.nl/ilwis/applications/application07.asp |archive-date=2010-08-15 |url-status=dead }} It was proposed by Chilean engineer Arturo Arias in 1970.

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

: $I\_A\; =\; \backslash frac\; \{\backslash pi\}\; \{2g\}\; \backslash int\_0^\{T\_d\}\; a\; (t)^2\; dt$ (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.{{cite web|url=http://www.geologie.ac.at/filestore/download/JB1471_193_A.pdf |archive-url=https://web.archive.org/web/20110531193712/http://www.geologie.ac.at/filestore/download/JB1471_193_A.pdf |url-status=dead |archive-date=2011-05-31 |title=Earthquake-Triggered Landslides in Austria – Dobratsch Revisited |author=Wolfgang A. Lenhardt |publisher=Jahrbuch der Geologischen Bundesanstalt |date=2007 }}

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