Magnitude (M)
Magnitude (M) : A number that represents the size of an earthquake source, as determined from seismographic observations. The original earthquake magnitude scale was the Richter or "local" scale (ML), defined by Charles Richter in 1935, but it has limited range and applicability. Modern magnitude scales are based on the area of fault rupture times the amount of slip (seismic moment).The moment magnitude (MW) is the preferred magnitude scale, as it provides the most reliable estimate of the size of the largest quakes. For smaller quakes, ML and MW values are nearly the same. An increase of one unit of moment magnitude (for example, from 4.6 to 5.6) corresponds approximately to a 31.6-fold increase in energy released [by definition, a two-unit increase in magnitude -for example, from 4.7 to 6.7-represents an increase in energy released of 1,000 times (31.6_31.6)]. Quakes below magnitude 2.5 are not generally felt by humans
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