The Earthquake Scale

The earthquake scale called the Richter magnitude scale gives a number to describe the amount of seismic energy released by an earthquake. It is a logarithmic scale meaning that an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.

Because of the logarithmic basis of the earthquake scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released.

Events with magnitudes of about 4.6 or greater on the earthquake scale are strong enough to be recorded by any of the seismographs in the world, as long as the seismograph's sensors are not located in an earthquake's shadow.

The following table describes the typical effects felt near the epicenter for earthquakes of various magnitudes on the earthquake scale. The noticed effects are determined not only be the magnitude on the earthquake scale but also on the distance to the epicenter, the depth of the earthquake and geological conditions in the area.

(Based on U.S. Geological Survey documents.)

Table of significant (not all) earthquakes since 2001. The list includes earthquakes of magnitude 7.0 or larger or that caused fatalities. Therefore, do not take the number of earthquakes listed with a magnitude below 7.0 as representative of their frequency.

From the table above, I compiled the number of worldwide earthquakes by year and by magnitude to produce the following chart. The trend is pretty obvious.

If you would like the most up-to-date information about recent earthquakes, how they measure on the earthquake scale and the number of deaths caused go to this site.