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Encyclopedia > Richter magnitude scale

The Richter magnitude scale, or more correctly local magnitude ML scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a Wood-Anderson torsion seismometer output. The effective limit of measurement for local magnitude is about ML=6.8. The energy release of an earthquake scales with the 3/2 power of the shaking amplitude, and thus a difference in magnitude of 1.0 is equivalent to a factor of 31.6 in the energy released; a difference of magnitude of 2.0 is equivalent to a factor of 1000 in the energy released. This article is about the natural seismic phenomenon. ... A logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. ... It has been suggested that pulse amplitude be merged into this article or section. ... Seismometers is of Greek origin and comes from Seism - the shakes and Meteo - I measure are instruments that measure and record motions of the ground, including those of seismic waves generated by earthquakes, nuclear explosions, and other seismic sources. ...

## Contents

Developed in 1935 by Charles Richter in partnership with Beno Gutenberg, both of the California Institute of Technology, the scale was originally intended to be used only in a particular study area in California, and on seismograms recorded on a particular instrument, the Wood-Anderson torsion seismometer. (Many[attribution needed] scientists and historians feel it should be known as the Richter-Gutenberg scale.) Richter originally reported values to the nearest quarter of a unit, but decimal numbers were used later. His motivation for creating the local magnitude scale was to separate the vastly larger number of smaller earthquakes from the few larger earthquakes observed in California at the time. 1935 (MCMXXXV) was a common year starting on Tuesday (link will display full calendar). ... Charles Francis Richter (April 26, 1900 – April 20, 1985), was an American seismologist, born in Hamilton, Ohio. ... Beno Gutenberg (June 4, 1889 â€“ January 25, 1960) was a German-born seismologist who made several important contributions to the science. ... The California Institute of Technology (commonly referred to as Caltech)[1] is a private, coeducational research university located in Pasadena, California, in the United States. ... This article is about the U.S. state. ... Seismometers is of Greek origin and comes from Seism - the shakes and Meteo - I measure are instruments that measure and record motions of the ground, including those of seismic waves generated by earthquakes, nuclear explosions, and other seismic sources. ...

His inspiration was the apparent magnitude scale used in astronomy to describe the brightness of stars and other celestial objects. Richter arbitrarily chose a magnitude 0 event to be an earthquake that would show a maximum combined horizontal displacement of 1 micrometre on a seismograph recorded using a Wood-Anderson torsion seismometer 100 km from the earthquake epicenter. This choice was intended to prevent negative magnitudes from being assigned. However, the Richter scale has no upper or lower limit, and sensitive modern seismographs now routinely record quakes with negative magnitudes. The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ...

Because of the limitations of the Wood-Anderson torsion seismometer used to develop the scale, the original ML cannot be calculated for events larger than about 6.8. Investigators have proposed extensions to the local magnitude scale, the most popular being the surface wave magnitude mS and the body wave magnitude mb. These traditional magnitude scales have largely been superseded by the implementation of methods for estimating the seismic moment and its associated moment magnitude scale. Body waves and surface waves Earthquake wave paths p-wave and s-wave from seismograph A seismic wave is a wave that travels through the Earth, most often as the result of a tectonic earthquake, sometimes from an explosion. ... The moment magnitude scale was introduced in 1979 by Tom Hanks and Hiroo Kanamori as a successor to the Richter scale and is used by seismologists to compare the energy released by earthquakes. ...

## Richter magnitudes

The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs (adjustments are included to compensate for the variation in the distance between the various seismographs and the epicenter of the earthquake). Because of the logarithmic basis of the 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. Look up logarithm in Wiktionary, the free dictionary. ... It has been suggested that pulse amplitude be merged into this article or section. ...

Events with magnitudes of about 4.6 or greater are strong enough to be recorded by any of the seismographs in the world.

The following describes the typical effects of earthquakes of various magnitudes near the epicenter. This table should be taken with extreme caution, since intensity and thus ground effects depend not only on the magnitude, but also on the distance to the epicenter, the depth of the earthquake's focus beneath the epicenter, and geological conditions (certain terrains can amplify seismic signals).

Richter Magnitudes Description Earthquake Effects Frequency of Occurrence
Less than 2.0 Micro Microearthquakes, not felt. About 8,000 per day
2.0-2.9 Minor Generally not felt, but recorded. About 1,000 per day
3.0-3.9 Minor Often felt, but rarely causes damage. 49,000 per year (est.)
4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.)
5.0-5.9 Moderate Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings. 800 per year
6.0-6.9 Strong Can be destructive in areas up to about 100 miles across in populated areas. 120 per year
7.0-7.9 Major Can cause serious damage over larger areas. 18 per year
8.0-8.9 Great Can cause serious damage in areas several hundred miles across. 1 per year
9.0-9.9 Great Devastating in areas several thousand miles across. 1 per 20 years
10.0+ Great Never recorded; see below for equivalent seismic energy yield. Extremely rare (Unknown)

(Based on U.S. Geological Survey documents.)[1]

Great earthquakes occur once a year, on average. The largest recorded earthquake was the Great Chilean Earthquake of May 22, 1960 which had a magnitude (MW) of 9.5.[2] Map showing the areas affected by the tsunami The Great Chilean Earthquake or Valdivian Earthquake (Terremoto de Valdivia in Spanish) of 22 May 1960 is the most intense earthquake ever recorded, rating a 9. ... is the 142nd day of the year (143rd in leap years) in the Gregorian calendar. ... Year 1960 (MCMLX) was a leap year starting on Friday (link will display full calendar) of the Gregorian calendar. ...

The following table lists the approximate energy equivalents in terms of TNT explosive force[3] - though note that the energy here is that of the underground energy release (ie a small atomic bomb blast will not simply cause light shaking of indoor items) rather than the overground energy release; the majority of energy transmission of an earthquake is not transmitted to and through the surface, but is instead dissipated into the crust and other subsurface structures. Unit of energy commonly used to quantify laerge amounts of energy. ...

Richter
Approximate Magnitude
Approximate TNT for
Seismic Energy Yield
Joule equivalent Example
0.5 5.6 kg (12.4 lb) 23.5 MJ large Hand grenade
1.0 32 kg (70 lb) 134.4 MJ Construction site blast
1.5 178 kg (392 lb) 747.6 MJ WWII conventional bombs
2.0 1 metric ton 4.2 GJ late WWII conventional bombs
2.5 5.6 metric tons 23.5 GJ WWII blockbuster bomb
3.0 32 metric tons 134.4 GJ Massive Ordnance Air Blast bomb
3.5 178 metric tons 747.6 GJ Chernobyl nuclear disaster, 1986
4.0 1 kiloton 4.2 TJ Small atomic bomb
5.0 32 kiloton 134.4 TJ Nagasaki atomic bomb (actual seismic yield was negligible since it detonated in the atmosphere)
2008 Lincolnshire earthquake
5.5 178 kilotons 747.6 TJ Little Skull Mtn., NV earthquake, 1992, Alum Rock, San Jose CA 2007
6.0 1 megaton 4.2 PJ Double Spring Flat, NV earthquake, 1994
6.7 5.6 megatons 23.5 PJ Northridge earthquake, 1994
7.1 50 megatons 210 PJ Tsar Bomba, largest thermonuclear weapon ever tested (magnitude seen on seismographs reduced because it detonated 4 km in the atmosphere.)
7.5 178 megatons 747.6 PJ 1976 Tangshan earthquake
2005 Kashmir earthquake
2007 Antofagasta earthquake
8.0 1 gigaton 4.2 EJ Toba eruption 75,000 years ago; and the Toba catastrophe theory, according to which modern human evolution was affected by this event
San Francisco, CA earthquake, 1906
Gujarat earthquake, 2001
Earthquake near Chincha Alta, Peru, August 2007
Earthquake near Indonesia September 12th 2007
9.0 31.6 gigatons 134.4 EJ 1964 Anchorage, AK earthquake
9.3 114 ?? gigatons ?? EJ 2004 Indian Ocean earthquake
9.5 178 gigatons 747.6 EJ 1960 Chile Earthquake
10.0 1 teraton 4.2 ZJ estimate for a 2 km rocky meteorite impacting at 25 km/s
12.0 160 teratons 672 ZJ Earth’s daily receipt of solar energy[3]

## References

1. ^ USGS: FAQ- Measuring Earthquakes
2. ^ USGS: List of World's Largest Earthquakes
3. ^ a b What is Richter Magnitude?, with mathematic equations

A seismic scale is used to measure and compare the relative severity of earthquakes. ... The moment magnitude scale was introduced in 1979 by Tom Hanks and Hiroo Kanamori as a successor to the Richter scale and is used by seismologists to compare the energy released by earthquakes. ... The Japan Meteorological Agency seismic intensity scale (éœ‡åº¦ shindo) is a measure used in Japan to indicate the strength of earthquakes. ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ...

Results from FactBites:

 Richter Magnitude (1477 words) Richter showed that, the larger the intrinsic energy of the earthquake, the larger the amplitude of ground motion at a given distance. He calibrated his scale of magnitudes using measured maximum amplitudes of shear waves on seismometers particularly sensitive to shear waves with periods of about one second. Both the magnitude and the seismic moment are related to the amount of energy that is radiated by an earthquake.
 Richter magnitude scale - Wikipedia, the free encyclopedia (688 words) It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a seismometer output. Richter arbitrarily chose a magnitude 0 event to be an earthquake that would show a maximum combined horizontal displacement of 1 micrometre on a seismogram recorded using a Wood-Anderson torsion seismometer 100 km from the earthquake epicenter. By the beginning of the 21st century, most seismologists considered the traditional magnitude scales to be largely obsolete, being replaced by a more physically meaningful measurement called the seismic moment which is more directly relatable to the physical parameters, such as the dimension of the earthquake rupture, and the energy released from the earthquake.
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