Richter Scale - Earthquake Magnitude
How are Earthquakes measured to determine their Magnitude?
Developed in California by Charles Richter with the help of Beno Gutenberg in 1935, the Richter Scale originally only reported values to the nearest quarter of a unit,but was later changed to report in 10 (decimal) increments. The Richter scale uses mathematical formulas to calculate and quantify the seismic energy released by an earthquake. While the magnitudes range from 0 to unlimited and whereas 0 is close to unmeasurable by technical instruments and magnitude 10 constitutes an earthquake never recorded by humans so far, the change in magnitude is not linear to the values assigned, but an increase of 0.2 in magnitude value corresponds to a doubling of seismic energy released.
In essence this means that a magnitude jump by one full number constitutes an increase of 31.6 times. A magnitude 4 earthquake therefore releases 31.6 times the energy of a magnitude 3 earthquake.
Richter Scale Values and average number of occurrences:
0.1 to 2.0 = Microearthquakes, not felt. / About 8,000 per day
2.0 to 2.9 = Generally not felt, but recorded. / About 1,000 per day
3.0 to 3.9 = Often felt, but rarely causes damage. / 49,000 per year (est.)
4.0 to 4.9 = Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. / 6,200 per year (est.)
5.0 to 5.9 = Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings. / 800 per year
6.0 to 6.9 = Can be destructive in areas up to about 160 kilometers (100 mi) across in populated areas. 120 per year
7.0 to 7.9 = Can cause serious damage over larger areas. / 18 per year
8.0 to 8.9 = Can cause serious damage in areas several hundred miles across. / 1 per year
9.0 to 9.9 = Devastating in areas several thousand miles across. / 1 per 20 years
10.0+ = Never recorded; see below for equivalent seismic energy yield.
For information on how to determine and measure Earthquake Intensity, please click: Mercalli Scale