Strong ground motion

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.

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.

"ShakeMaps" are produced by the United States Geological Survey, provide almost-real-time information about significant earthquake events, and can assist disaster-relief teams and other agencies.