"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 and/or motion:
“Hast ever ben in Omaha
Where rolls the dark Missouri down,
Where four strong horses scarce can draw
An empty wagon through the town?
Where sand is blown from every mound
To fill your eyes and ears and throat;
Where all the steamboats are aground,
And all the houses are afloat?...
If not, take heed to what I say,
You’ll find it just as I have found it;
And if it lies upon your way
For God’s sake, reader, go around it!”
—For the State of Nebraska, U.S. public relief program (1935-1943)
“subways, rivered under streets
and rivers . . . in the car
the overtone of motion
underground, the monotone
of motion is the sound
of other faces, also underground—”
—Hart Crane (1899–1932)