Glossary of earthquake terms
Compare the fault area of the magnitude 7.3 (top) with
that of the magnitude 5.6 (smallest one near the bottom).
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Magnitude
The magnitude
is a
number that characterizes the relative size of an earthquake.
Magnitude is based on measurement of the maximum motion
recorded by a seismograph.
Several scales have been defined, but the most commonly
used are (1) local magnitude (ML), commonly referred to
as "Richter magnitude," (2) surface-wave magnitude (Ms),
(3) body-wave magnitude (Mb), and (4) moment magnitude (Mw).
Scales 1-3 have limited range and applicability and do not
satisfactorily measure the size of the largest earthquakes.
The moment magnitude (Mw) scale, based on the concept of
seismic moment, is uniformly
applicable to all sizes of earthquakes but is more difficult
to compute than the other types. All magnitude scales should
yield approximately the same value for any given earthquake.
See also:
Earthquake
ABC's & FAQ discussion.
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