spectral acceleration

{{Short description|Unit for measuring earthquakes}}

File:Hawaii 1998 0p2s 2p50.png hazard map for Hawaii, based on a 2% probability of exceeding 0.2 second spectral acceleration at 5 Hz in 50 years]]

Spectral acceleration (SA) is a unit measured in g (the acceleration due to Earth's gravity, equivalent to g-force) that describes the maximum acceleration in an earthquake on an object – specifically a damped, harmonic oscillator moving in one physical dimension. This can be measured at (or specified for) different oscillation frequencies and with different degrees of damping, although 5% damping is commonly applied.[http://www.opensha.org/glossary-intensityMeasureType#SA Intensity Measure Type (IMT)] {{Webarchive|url=https://web.archive.org/web/20151004034153/http://www.opensha.org/glossary-intensityMeasureType#SA |date=2015-10-04 }} OpenSHA, accessed 2011-04-14 The SA at different frequencies may be plotted to form a response spectrum.

Spectral acceleration, with a value related to the natural frequency of vibration of the building, is used in earthquake engineering and gives a closer approximation to the motion of a building or other structure in an earthquake than the peak ground acceleration value,[https://earthquake.usgs.gov/learn/faq/?faqID=221 FAQs – What is "spectral acceleration" or SA?] United States Geological Survey, accessed 2011-04-14 although there is normally a correlation between [short period] SA and PGA.

Some seismic hazard maps are also produced using spectral acceleration.