The strength of an earthquake can also be measured and expressed in terms of the magnitude of energy released by the earthquake.
Seismologist Charles Richter devised his system based on the amplitude of the seismic waves recorded by seismographs. When the data from several seismometers are compared a measure of magnitude can be realized within minutes of the earthquake activity.
The Richter scale is logarithmic. An increase in magnitude of one unit corresponds to a tenfold increase in the size of an earthquake. Thus an earthquake of magnitude 6 is ten times larger than one of magnitude 5, and a hundred times larger than one of magnitude 4.
globally per year
|Typical Intensity at center|
(see Mercalli Scale)
% of gravity (g)
|8.0 +||0.1 – 0.2||XII||–|
|7.4 – 8.0||4||XI||–|
|7.0 – 7.3||15||X||70|
|6.2 – 6.9||100||VIII – IX||15 – 32|
|5.5 – 6.1||500||VII||7|
|4.9 – 5.4||1,400||VI||3|
|4.3 – 4.8||4,800||IV-V||0.7-1.5|
|3.5 – 4.2||30,000||II – III||0.2 – 0.3|
|2.0 – 3.4||800,000||I – II||0.1 – 0.2|