"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:
“You mustn’t give your heart to a wild thing. The more you do, the stronger they get. Until they’re strong enough to run into the woods or fly into a tree. And then to a higher tree. And then to the sky.”
—George Axelrod (b. 1922)
“The ground for taking ignorance to be restrictive of freedom is that it causes people to make choices which they would not have made if they had seen what the realization of their choices involved.”
—A.J. (Alfred Jules)
“All the phenomena which surround him are simple and grand, and there is something impressive, even majestic, in the very motion he causes, which will naturally be communicated to his own character, and he feels the slow, irresistible movement under him with pride, as if it were his own energy.”
—Henry David Thoreau (1817–1862)