Spectral acceleration

Short description: Unit for measuring earthquakes

Ground motion 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.[1] 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,[1][2] although there is normally a correlation between [short period] SA and PGA.[2]

Some seismic hazard maps are also produced using spectral acceleration.

## See also

* Seismic scale

## External links

* Spectral Acceleration Hazard Map of California – for 1 sec period
* 2005 National Building Code of Canada – Spectral Acceleration Hazard Maps for various periods
* Revision of Time-Independent Probabilistic Seismic Hazard Maps for Alaska
* What is a ground shaking hazard map? – Includes explanations of SA and PGA

## References

1. ↑ 1.0 1.1 Intensity Measure Type (IMT) OpenSHA, accessed 2011-04-14
2. ↑ 2.0 2.1 FAQs – What is "spectral acceleration" or SA? United States Geological Survey, accessed 2011-04-14

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