"Peak ground velocity" redirects here.
Seismologists usually define strong ground motion as the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forcing the use of accelerographs (or strong ground motion accelerometers) for recording.
As seismic instruments (and accelerometers in particular) become more common, it becomes necessary to correlate expected damage with instrument-readings. The old Modified Mercalli intensity scale (MM), a relic of the pre-instrument days, remains useful in the sense that each intensity-level provides an observable difference in seismic damage.
After many years of trying every possible manipulation of accelerometer-time histories, it turns out that the extremely simple peak ground velocity (PGV) provides the best correlation with damage. PGV merely expresses the peak of the first integration of the acceleration record. Accepted formulae now link PGV with MM Intensity. Note that the effect of soft soils gets built into the process, since one can expect that these foundation conditions will amplify the PGV significantly.
ShakeMap systems tie all of this together into a useful product. Some systems use seismometers and accelerometers to produce a near-instantaneous map of expected MM Intensities after a significant earthquake. As well, people can send in their observations of earthquake effects to help fill in the maps, which can help disaster-relief teams and other agencies.
The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, rupture velocity, etc.
Famous quotes containing the words strong, ground and/or motion:
“At present, man applies to nature but half his force. He works on the world with his understanding alone. He lives in it, and masters it by a penny-wisdom; and he that works most in it, is but a half-man, and whilst his arms are strong and his digestion good, his mind is imbruted, and he is a selfish savage.”
—Ralph Waldo Emerson (1803–1882)
“If you are looking down while you are walking it is better to walk up hill the ground is nearer.”
—Gertrude Stein (1874–1946)
“Happier of happy though I be, like them
I cannot take possession of the sky,
Mount with a thoughtless impulse, and wheel there,
One of a mighty multitude whose way
And motion is a harmony and dance
Magnificent.”
—William Wordsworth (1770–1850)