"Peak ground velocity" redirects here.

Seismologist

Seismology

Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...

s usually define strong ground motion as the strong earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

 shaking that occurs close to (less than about 50 km from) a causative fault

Geologic fault

In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of tectonic forces...

. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer

Seismometer

Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources...

, forcing the use of accelerograph

Accelerograph

An accelerograph can be referred to as a strong motion seismograph, or simply as an earthquake accelerometer. They are usually constructed as a self-contained box, more commonly now being connected directly to the Internet....

s (or strong ground motion accelerometer

Accelerometer

An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...

s) 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

Mercalli intensity scale

The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude M_w usually reported for an earthquake , which is a measure of the energy released...

 (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

Integral

Integration is an important concept in mathematics and, together with its inverse, differentiation, is one of the two main operations in calculus...

 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

Emergency management

Emergency management is the generic name of an interdisciplinary field dealing with the strategic organizational management processes used to protect critical assets of an organization from hazard risks that can cause events like disasters or catastrophes and to ensure the continuance of the...

 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.

External links

• A paper describing how the Alaska Pipeline dealt with the toughest engineering challenge of all: straddling an active fault
  Active fault
  An active fault is a fault that is likely to have another earthquake sometime in the future. Faults are commonly considered to be active if there has been movement observed or evidence of seismic activity during the last 10,000 years....