Strong ground motion
"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.
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- Wu, Yih-Min; Hsiao, Nai-Chi; Teng, Ta-Liang (July 2004). "Relationships between Strong Ground Motion Peak Values and Seismic Loss during the 1999 Chi-Chi, Taiwan Earthquake". Natural Hazards (Kluwer Academic Publishers). Volume 32 (Issue 3): pp 357–373. doi:10.1023/B:NHAZ.0000035550.36929.d0.
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- Mahalia Miller, Lynne Burks, and Reza Bosagh Zadeh Rapid Estimate of Ground Shaking Intensity by Combining Simple Earthquake Characteristics with Tweets, Tenth U.S. National Conference on Earthquake Engineering
- Reza Bosagh Zadeh Using Twitter to measure earthquake impact in almost real time, Twitter Engineering