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PGA records the acceleration (rate of change of speed) of these movements, while peak ground velocity is the greatest speed (rate of movement) reached by the ground, and peak displacement is the distance moved. [7] [8] These values vary in different earthquakes, and in differing sites within one earthquake event, depending on a number of ...
This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or strength of an earthquake – an event occurring at greater or lesser depth. (The "M w" scale is widely used.) The MM scale measures intensity of shaking, at any particular location, on the surface.
An earthquake's seismic moment can be estimated in various ways, which are the bases of the M wb, M wr, M wc, M ww, M wp, M i, and M wpd scales, all subtypes of the generic M w scale. See Moment magnitude scale § Subtypes for details. Seismic moment is considered the most objective measure of an earthquake's "size" in regard of total energy. [50]
The 1983 Borah Peak earthquake occurred on October 28, at 8:06:09 a.m. MDT in the western United States, in the Lost River Range at Borah Peak in central Idaho. [5] [6] [7]The shock measured 6.9 on the moment magnitude scale and had a maximum Mercalli intensity of IX (Violent).
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.
Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake. They are distinguished from seismic magnitude scales , which measure the magnitude or overall strength of an earthquake, which may, or perhaps may not, cause perceptible shaking.
By analysing seismic waves generated by earthquakes, the velocity structure can be studied which can reflect the subsurface condition where the seismic wave propagated. Receiver Function Analysis Receiver function analysis is a seismic method that interprets waveform data to study the conversions and reflections of seismic waves at subsurface ...
Some maps released by the USGS are shown with peak ground acceleration with a 10% probability of exceedance in 50 years, measured in Metre per second squared.For parts of the US, the National Seismic Hazard Mapping Project in 2008 resulted in seismic hazard maps showing peak acceleration (as a percentage of gravity) with a 2% probability of exceedance in 50 years.