Richter scale: Difference between revisions
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{{Short description|Measure of an earthquake's strength}} |
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{{about||the American seismologist|Charles Richter|a review of different magnitude scales|seismic magnitude scales}} |
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{{about|the earthquake magnitude scale introduced by Charles Richter in 1935|a review of earthquake magnitude scales|seismic magnitude scales|the musical scale used for tuning harmonicas|Richter tuning|the single by EPMD|Richter Scale (song)}} |
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{{use mdy dates|date=February 2013}} |
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{{Use mdy dates|date=August 2024}} |
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{{Earthquakes}} |
{{Earthquakes}} |
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The '''Richter scale'''<ref>{{Harvnb|Kanamori|1978|p=411}}. {{Harvtxt|Hough|2007|pp=122–126}} discusses the name at some length.</ref> ({{IPAc-en|ˈ|r|ɪ|k|t|ər}}), also called the '''Richter magnitude scale''', '''Richter's magnitude scale''', and the '''Gutenberg–Richter scale''',<ref>{{cite book |last1=McPhee |first1=John |title=Annals of the Former World |date=1998 |publisher=Farrar, Straus and Giroux |page=608}}</ref> is a measure of the strength of [[earthquake]]s, developed by [[Charles Richter]] in collaboration with [[Beno Gutenberg]], and presented in Richter's landmark 1935 paper, where he called it the "magnitude scale".<ref>{{Harvnb|Kanamori|1978|p=411}}; {{Harvnb|Richter|1935}}.</ref> This was later revised and renamed the '''local magnitude scale''', denoted as ML or {{M|L}}.<ref name="ReferenceA">{{Harvnb|Gutenberg|Richter|1956b|p=30}}.</ref> |
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The so-called '''Richter magnitude scale''' – more accurately, ''Richter's magnitude scale'', or just ''Richter magnitude'' – for measuring the strength ("size") of earthquake refers to the original "magnitude scale" developed by [[Charles F. Richter]] and presented in his landmark 1935 paper, and later revised and renamed the '''Local magnitude scale''', denoted as "ML" or "M<sub>L</sub>". Because of various shortcomings of the ML scale most seismological authorities now use other scales, such as the [[moment magnitude scale]] ({{M|w}}), to report earthquake magnitudes, but much of the news media still refers to these as "Richter" magnitudes. All magnitude scales retain the [[logarithm]]ic character of the original, and are scaled to have roughly comparable numeric values. |
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Because of various shortcomings of the original {{M|L}} scale, most seismological authorities now use other similar scales such as the [[moment magnitude scale]] ({{M|w}}) to report earthquake magnitudes, but much of the news media still erroneously refers to these as "Richter" magnitudes. All magnitude scales retain the [[logarithm]]ic character of the original and are scaled to have roughly comparable numeric values (typically in the middle of the scale). Due to the variance in earthquakes, it is essential to understand the Richter scale uses [[common logarithm]]s simply to make the measurements manageable (i.e., a magnitude 3 quake factors 10³ while a magnitude 5 quake factors 10<sup>5</sup> and has seismometer readings 100 times larger).<ref>{{Cite web|title=Discovery Project 17: Orders of Magnitude|url=https://www.stewartmath.com/precalc_7e_dp/precalc_7e_dp17.html|access-date=February 24, 2022|website=stewartmath.com}}</ref> |
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== Development == |
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[[File:CharlesRichter.jpg|thumb|upright|[[Charles Francis Richter]] (circa 1970)]] |
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Prior to the development of the magnitude scale the only measure of an earthquake's strength or "size" was a subjective assessment of the intensity of shaking observed near the [[epicenter]] of the earthquake, categorized by various [[seismic intensity scales]] such as the [[Rossi-Forel scale]]. In 1883 [[John Milne]] surmised that the shaking of large earthquakes might generate waves detectable around the globe, and in 1899 E. Von Rehbur Paschvitz observed in Germany seismic waves attributable to an earthquake in Tokyo.<ref>{{Harvnb|Bolt|1993|p=47}}.</ref> In the 1920s [[Harry O. Wood]] and [[John August Anderson|John A. Anderson]] developed the [[Wood–Anderson seismograph]], one of the first practical instruments for recording seismic waves.<ref>{{Harvnb|Hough|2007|p=}};</ref> Wood then built, under the auspices of the [[California Institute of Technology]] and the [[Carnegie Institution for Science|Carnegie Institute]], a network of seismographs stretching across [[Southern California]].<ref>{{Harvnb|Hough|2007|p=57}}.</ref> He also recruited the young and unknown Charles Richter to measure the seismograms and locate the earthquakes generating the seismic waves.<ref>{{Harvnb|Hough|2007|pp=57, 116}}.</ref> |
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In 1931 [[Kiyoo Wadati]] showed how he had measured, for several strong earthquakes in Japan, the amplitude of the shaking observed at various distances from the epicenter. He then plotted the logarithm of the amplitude against the distance, and found a series of curves that showed a rough correlation with the estimated magnitudes of the earthquakes.<ref>{{Harvnb|Richter|1935|p=2}}.</ref> Richter resolved some difficulties with this method,<ref>{{Harvnb|Richter|1935|pp=1–5}}.</ref> then, using data collected by his colleague [[Beno Gutenberg]], produced similar curves, confirming that they could be used to compare the relative magnitudes of different earthquakes.<ref>{{Harvnb|Richter|1935|pp=2–3}}.</ref> |
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To produce a practical method of assigning an absolute measure of magnitude required additional developments. First, to span the wide range of possible values Richter adopted Gutenberg's suggestion of a [[logarithm]]ic scale, where each step represents a tenfold increase of magnitude, similar to the magnitude scale used by astronomers for star brightness.<ref>[pending]</ref> Second, he wanted a magnitude of zero to be around the limit of human perceptibility.<ref>{{Harvnb|Richter|1935|p=14}}: {{Harvnb|Gutenberg|Richter|1936|p=183}}.</ref> Third, he specified the Wood–Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in [[microns]]", measured at a distance of 100 km. The scale was calibrated by defining a magnitude 3 shock as one that produces (at a distance of 100 km) a maximum amplitude of 1 micron (1 µm, or 0.001 millimeters) on a seismogram recorded by a Wood–Anderson torsion seismograph.<ref>{{Harvnb|Richter|1935|p=5}}. See also {{Harvnb|Hutton|Boore|1987|p=1}}; {{Harvnb|Chung|Bernreuter|1980|p=10}}.</ref> Finally, Richter calculated a table of distance corrections,<ref>{{Harvnb|Richter|1935|p=6}}, Table I.</ref> in that for distances less than 200 kilometers<ref>{{Harvnb|Richter|1935|p=32}}.</ref> the attenuation is strongly affected by the structure and properties of the regional geology.<ref>{{Harvnb|Chung|Bernreuter|1980|p=5}}.</ref> |
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When Richter presented the resulting scale in 1935 he called it (at the suggestion of Harry Wood) simply a "magnitude" scale.<ref>{{Harvnb|Richter|1935|p=1}}. His article is titled: "An Instrumental Earthquake Magnitude Scale".</ref> "Richter magnitude" appears to have originated when Perry Byerly told the press that the scale was Richter's, and "should be referred to as such."<ref>{{Harvnb|Hough|2007|pp=123–124}}.</ref> In 1956 Gutenberg and Richter, while still referring to "magnitude scale", labelled it "local magnitude", with the symbol {{M|L}}, to distinguish it from two other scales they had developed, the [[surface wave magnitude]] (M<sub>S</sub>) and [[body wave magnitude]] (M<sub>B</sub>)<!-- These are non-standard: do not use the "M" template here. --> scales.<ref>{{Harvnb|Gutenberg|Richter|1956b|p=30}}.</ref> |
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==Details== |
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The Richter scale was defined in 1935 for particular circumstances and instruments; the particular circumstances refer to it being defined for Southern California and "implicitly incorporates the [[attenuation|attenuative]] properties of Southern California crust and mantle."<ref>{{cite web |url=https://earthquake.usgs.gov/earthquakes/eqarchives/mineblast/definitions.php |title=Explanation of Bulletin Listings, USGS}}</ref> The particular instrument used would become saturated by strong earthquakes and unable to record high values. The scale was replaced in the 1970s by the [[moment magnitude scale]] (MMS, symbol {{M|w}}); for earthquakes adequately measured by the Richter scale, numerical values are approximately the same. Although values measured for earthquakes now are <math>M_w</math> (MMS), they are frequently reported by the press as Richter values, even for earthquakes of magnitude over 8, when the Richter scale becomes meaningless. |
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Anything above 5 is classified as a risk by the USGS.{{citation needed|date=April 2013}} |
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The Richter and MMS scales measure the energy released by an earthquake; another scale, the [[Mercalli intensity scale]], classifies earthquakes by their ''effects'', from detectable by instruments but not noticeable, to catastrophic. The energy and effects are not necessarily strongly correlated; a shallow earthquake in a populated area with soil of certain types can be far more intense in effects than a much more energetic deep earthquake in an isolated area. |
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Several scales have historically been described as the "Richter scale", especially the ''local magnitude'' <math>M_\text{L}</math> and the surface wave <math>M_\text{s}</math> scale. In addition, the ''body wave magnitude'', <math>m_\text{b}</math>, and the ''moment magnitude'', <math>M_\text{w}</math>, abbreviated MMS, have been widely used for decades. A couple of new techniques to measure magnitude are in the development stage by seismologists. |
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All magnitude scales have been designed to give numerically similar results. This goal has been achieved well for <math>M_\text{L}</math>, <math>M_\text{s}</math>, and <math>M_\text{w}</math>.<ref>{{Harvnb|Richter|1935}}.</ref><ref>Richter, C.F., "Elementary Seismology", ed, Vol., W. H. Freeman and Co., San Francisco, 1956.</ref> The <math>m_\text{b}</math> scale gives somewhat different values than the other scales. The reason for so many different ways to measure the same thing is that at different distances, for different [[hypocenter|hypocentral]] depths, and for different earthquake sizes, the amplitudes of different types of elastic waves must be measured. |
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<math>M_\text{L}</math> is the scale used for the majority of earthquakes reported (tens of thousands) by local and regional seismological observatories. For large earthquakes worldwide, the moment magnitude scale (MMS) is most common, although <math>M_\text{s}</math> is also reported frequently. |
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The [[seismic moment]], '''''<math>M_o</math>''''', is proportional to the area of the rupture times the average slip that took place in the earthquake, thus it measures the physical size of the event. <math>M_\text{w}</math> is derived from it empirically as a quantity without units, just a number designed to conform to the <math>M_\text{s}</math> scale.<ref>Hanks, T. C. and H. Kanamori, 1979, "Moment magnitude scale", ''Journal of Geophysical Research,'' 84, B5, 2348.</ref> A spectral analysis is required to obtain <math>M_o</math>, whereas the other magnitudes are derived from a simple measurement of the amplitude of a specifically defined wave. |
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All scales, except <math>M_\text{w}</math>, saturate for large earthquakes, meaning they are based on the amplitudes of waves which have a wavelength shorter than the rupture length of the earthquakes. These short waves (high frequency waves) are too short a yardstick to measure the extent of the event. The resulting effective upper limit of measurement for <math>M_L</math> is about 7 and about 8.5<ref>{{cite web |url=http://www.weather.gov.hk/education/edu02rga/article/ele-EarthquakeMagnetude_e.htm |title=On Earthquake Magnitudes |first=Wang-chun |last=Woo |date=September 2012 |publisher=Hong Kong Observatory |accessdate=18 December 2013}}</ref> for <math>M_\text{s}</math>.<ref name="Local magnitude">{{cite web |url=https://earthquake.usgs.gov/hazards/qfaults/glossary.php |title=Richter scale |work=Glossary |publisher=[[United States Geological Survey|USGS]] |date=March 31, 2010 }}</ref> |
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New techniques to avoid the saturation problem and to measure magnitudes rapidly for very large earthquakes are being developed. One of these is based on the long period P-wave;<ref>Di Giacomo, D., Parolai, S., Saul, J., Grosser, H., Bormann, P., Wang, R. & Zschau, J., 2008. "Rapid determination of the energy magnitude Me," in ''European Seismological Commission 31st General Assembly,'' Hersonissos.</ref> the other is based on a recently discovered channel wave.<ref>Rivera, L. & Kanamori, H., 2008. "Rapid source inversion of W phase for tsunami warning," in ''European Geophysical Union General Assembly,'' pp. A-06228, Vienna.</ref> |
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The [[energy]] release of an earthquake,<ref>Marius Vassiliou and Hiroo Kanamori (1982): "The Energy Release in Earthquakes," ''Bull. Seismol. Soc. Am.'' 72, 371–387.</ref> which closely correlates to its destructive power, scales with the {{frac|3|2}} power of the shaking amplitude. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 (<math>=({10^{1.0}})^{(3/2)}</math>) in the energy released; a difference in magnitude of 2.0 is equivalent to a factor of 1000 (<math>=({10^{2.0}})^{(3/2)}</math>) in the energy released.<ref>{{cite journal|authors=William Spence, Stuart A. Sipkin, and George L. Choy |url=https://earthquake.usgs.gov/learn/topics/measure.php |title=Measuring the Size of an Earthquake |journal=Earthquakes and Volcanoes |volume=21 |number=1 |year=1989}}</ref> The elastic energy radiated is best derived from an integration of the radiated spectrum, but an estimate can be based on <math>m_\text{b}</math> because most energy is carried by the high frequency waves. |
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==Richter magnitudes== |
==Richter magnitudes== |
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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. The original formula is:<ref name="Ellsworth">{{cite book |
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[[Image:Earthquake_severity.jpg|thumb| ]] |
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|publisher=United States Geological Survey |
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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). The original formula is:<ref>{{cite journal |
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|last=Ellsworth |
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| publisher=USGS |
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|first=William L. |
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| last=Ellsworth |
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|chapter-url=http://www.johnmartin.com/earthquakes/eqsafs/safs_693.htm |
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| first=William L. |
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|chapter=The Richter Scale ML |
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| url=http://www.johnmartin.com/earthquakes/eqsafs/safs_693.htm |
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|title=The San Andreas Fault System, California |
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|editor-first=Robert E. |
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| pages=c6, p177 |
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|editor-last=Wallace |
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| year=1991 |
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|id=Professional Paper 1515 |
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| accessdate=2008-09-14 |
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|page=177 |
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}} |
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|year=1991 |
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</ref> |
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|access-date=September 14, 2008 |
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|archive-date=April 25, 2016 |
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|archive-url=https://web.archive.org/web/20160425121745/http://www.johnmartin.com/earthquakes/eqsafs/safs_693.htm |
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|url-status=dead |
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}}</ref> |
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:<math>M_\mathrm{L} = \log_{10} A - \log_{10} A_\mathrm{0}(\delta) = \log_{10} [A / A_\mathrm{0}(\delta)],\ </math> |
:<math display="block">M_\mathrm{L} = \log_{10} A - \log_{10} A_\mathrm{0}(\delta) = \log_{10} [A / A_\mathrm{0}(\delta)],\ </math> |
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where A is the maximum excursion of the |
where {{mvar|A}} is the maximum excursion of the [[Wood-Anderson seismograph]], the empirical function {{mvar|A<sub>0</sub>}} depends only on the [[epicentral distance]] of the station, <math>\delta</math>. In practice, readings from all observing stations are averaged after adjustment with station-specific corrections to obtain the {{M|L}} value.<ref name="Ellsworth" /> |
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Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude |
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, and each increase of 0.2 corresponds to approximately a doubling of the energy released. |
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Events with magnitudes greater than 4.5 are strong enough to be recorded by a seismograph anywhere in the world, so long as its sensors are not located in the earthquake's [[Shadow zone|shadow]].<ref>{{Cite journal|last=Brush|first=Stephen G.|date=September 1980|title=Discovery of the Earth's core|url=http://aapt.scitation.org/doi/10.1119/1.12026|journal=American Journal of Physics|language=en|volume=48|issue=9|pages=705–724|doi=10.1119/1.12026|issn=0002-9505}}</ref><ref>{{Cite book |title=A dictionary of earth sciences.|date=2008|author=Michael Allaby|isbn=978-0-19-921194-4|edition=3rd |location=Oxford|oclc=177509121}}</ref><ref>{{Cite journal|last=Einarsson|first=P.|date=September 1978|title=S-wave shadows in the Krafla Caldera in NE-Iceland, evidence for a magma chamber in the crust|url=http://dx.doi.org/10.1007/bf02597222|journal=Bulletin Volcanologique|volume=41|issue=3|pages=187–195|doi=10.1007/bf02597222|issn=0258-8900|hdl=20.500.11815/4200|hdl-access=free}}</ref> |
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Events with magnitudes greater than 4.5 are strong enough to be recorded by a seismograph anywhere in the world, so long as its sensors are not located in the earthquake's [[Seismic shadowing|shadow]].{{cn|date=November 2018}} |
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The following describes the typical effects of earthquakes of various magnitudes near the epicenter. The values are typical |
The following describes the typical effects of earthquakes of various magnitudes near the epicenter.<ref name="GNSScience1">{{cite web | url=https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-Richter-Magnitude-Scale | title=What is the Richter Magnitude Scale? | publisher=[[GNS Science]] | access-date=August 3, 2021 | url-status=dead | archive-url=https://web.archive.org/web/20210803200647/https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-Richter-Magnitude-Scale |archive-date=August 3, 2021}}</ref> The values are typical and may not be exact in a future event because intensity and ground effects depend not only on the magnitude but also on (1) the distance to the epicenter, (2) the depth of the earthquake's focus beneath the epicenter, (3) the location of the epicenter, and (4) [[Seismic site effects|geological conditions]]. |
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{| class="wikitable" |
{| class="wikitable" |
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!Magnitude |
!Magnitude |
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!Description |
!Description |
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!Typical maximum [[Modified Mercalli intensity scale|modified Mercalli intensity]]<ref>{{cite web|title=Magnitude / Intensity Comparison|url=http://earthquake.usgs.gov/learn/topics/mag_vs_int.php|url-status=dead|archive-url=https://web.archive.org/web/20110623113247/http://earthquake.usgs.gov/learn/topics/mag_vs_int.php|archive-date=June 23, 2011}}</ref> |
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![[Mercalli intensity scale|Mercalli intensity]] |
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!Average earthquake effects |
!Average earthquake effects |
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!Average frequency of occurrence (estimated) |
!Average frequency of occurrence globally (estimated) |
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|1.0–1.9 |
|style="background:lightskyblue;"|1.0–1.9 |
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|[[Microearthquake|Micro]] |
|[[Microearthquake|Micro]] |
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|I |
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|<span style="color:silver">I</span> |
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|Microearthquakes, not felt |
|Microearthquakes, not felt. Recorded by seismographs.<ref>This is what Richter wrote in his ''Elementary Seismology'' (1958), an opinion copiously reproduced afterward in Earth's science primers. Recent evidence shows that earthquakes with negative magnitudes (down to −0.7) can also be felt in exceptional cases, especially when the focus is very shallow (a few hundred meters). See: Thouvenot, F.; Bouchon, M. (2008). "What is the lowest magnitude threshold at which an earthquake can be felt or heard, or objects thrown into the air?," in Fréchet, J., Meghraoui, M. & Stucchi, M. (eds), ''Modern Approaches in Solid Earth Sciences'' (vol. 2), ''Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes,'' Springer, Dordrecht, 313–326.</ref> |
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|Continual/several million per year |
|Continual/several million per year |
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|- |
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|2.0–2.9 |
|style="background:paleturquoise;"|2.0–2.9 |
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|rowspan=" |
|rowspan="1"|Minor |
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|I |
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|<span style="color:silver">I</span> to <span style="color:#bfccff">II</span> |
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|Felt slightly by some people. No damage to buildings. |
|Felt slightly by some people. No damage to buildings. |
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|Over one million per year |
|Over one million per year |
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|- |
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|3.0–3.9 |
|style="background:palegreen;"|3.0–3.9 |
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|rowspawn "1"|Slight |
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|<span style="color:#99f">III</span> to <span style="color:#8ff">IV</span> |
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|II to III |
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|Often felt by people, but very rarely causes damage. Shaking of indoor objects can be noticeable. |
|Often felt by people, but very rarely causes damage. Shaking of indoor objects can be noticeable. |
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|Over 100,000 per year |
|Over 100,000 per year |
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|- |
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|4.0–4.9 |
|style="background:greenyellow;"|4.0–4.9 |
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|Light |
|Light |
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|IV to V |
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|<span style="color:#8ff">IV</span> to <span style="color:#ff0">VI</span> |
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|Noticeable shaking of indoor objects and rattling noises. Felt by most people in the affected area. Slightly felt outside. Generally causes |
|Noticeable shaking of indoor objects and rattling noises. Felt by most people in the affected area. Slightly felt outside. Generally causes zero to minimal damage. Moderate to significant damage is very unlikely. Some objects may fall off shelves or be knocked over. |
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|10,000 to 15,000 per year |
|10,000 to 15,000 per year |
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|- |
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|5.0–5.9 |
|style="background:yellow;"|5.0–5.9 |
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|Moderate |
|Moderate |
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|VI to VII |
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|<span style="color:#ff0">VI</span> to <span style="color:#fd0">VII</span> |
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|Can cause damage of varying severity to poorly constructed buildings. |
|Can cause damage of varying severity to poorly constructed buildings. Zero to slight damage to all other buildings. Felt by everyone. |
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|1,000 to 1,500 per year |
|1,000 to 1,500 per year |
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|- |
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|6.0–6.9 |
|style="background:gold;"|6.0–6.9 |
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|Strong |
|Strong |
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|VII to IX |
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|<span style="color:#ff9100">VIII</span> to <span style="color:#d00">X</span> |
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|Damage to a moderate number of well-built structures in populated areas. [[Earthquake-resistant structures]] survive with slight to moderate damage. Poorly designed structures receive moderate to severe damage. Felt in wider areas; up to hundreds of |
|Damage to a moderate number of well-built structures in populated areas. [[Earthquake-resistant structures]] survive with slight to moderate damage. Poorly designed structures receive moderate to severe damage. Felt in wider areas; up to hundreds of kilometers from the epicenter. Strong to violent shaking in the epicentral area. |
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|100 to 150 per year |
|100 to 150 per year |
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|- |
|- |
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|style="color:white; background:darkorange;"|7.0–7.9 |
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|7.0–7.9 |
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|Major |
|Major |
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|rowspan="3"| VIII or higher |
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|rowspan="3"| <span style="color:#d00">X</span> or greater<ref>{{cite web |url=http://www.city-data.com/city/Anchorage-Alaska.html|title=Anchorage, Alaska (AK) profile: population, maps, real estate, averages, homes, statistics, relocation, travel, jobs, hospitals, schools, crime, moving, houses, news |publisher=City-Data.com |accessdate=2012-10-12 }}</ref> |
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|Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Felt across great distances with major damage mostly limited to 250 km from epicenter. |
|Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Felt across great distances with major damage mostly limited to 250 km from the epicenter. |
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|10 to 20 per year |
|10 to 20 per year |
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|- |
|- |
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|8.0–8.9 |
|style="color:white; background:red;"|8.0–8.9 |
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|rowspan=" |
|rowspan="1"|Great |
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|Major damage to buildings, structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake-resistant buildings. Damaging in large areas. Felt in extremely large regions. |
|Major damage to buildings, and structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake-resistant buildings. Damaging in large areas. Felt in extremely large regions. |
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|One per year |
|One per year |
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|- |
|- |
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|style="color:white; background:maroon;"|9.0–9.9 |
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|9.0 and greater |
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|rowspawn"1"|Extreme |
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|At or near total destruction – severe damage or collapse to all buildings. Heavy damage and shaking extends to distant locations. Permanent changes in ground topography. |
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|Near total destruction – severe damage or collapse to all buildings. Heavy damage and shaking extend to distant locations. Permanent changes in ground topography. |
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|One per 10 to 50 years |
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|One to three per century<ref name="McCaffrey2008">{{cite journal | title=Global frequency of magnitude 9 earthquakes | first=R. | last=McCaffrey | journal=Geology | date=2008 | volume=36 | issue=3 | pages=263–266 | doi=10.1130/G24402A.1}}</ref> |
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|} |
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(''Based on U.S. Geological Survey documents.'')<ref>{{cite web |url=https://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php |title=Earthquake Facts and Statistics |publisher=United States Geological Survey |date= |
(''Based on U.S. Geological Survey documents.'')<ref>{{cite web |url=https://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php |title=Earthquake Facts and Statistics |publisher=United States Geological Survey |date=November 29, 2012 |access-date=December 18, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20100524161817/http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php |archive-date=May 24, 2010 }}</ref> |
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The intensity and death toll depend on several factors (earthquake depth, epicenter location, population density, to name a few) and can vary widely. |
The intensity and death toll depend on several factors (earthquake depth, epicenter location, and population density, to name a few) and can vary widely. |
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Millions of minor earthquakes occur every year worldwide, equating to hundreds every hour every day.<ref name="IRIS">{{cite web|title=How Often Do Earthquakes Occur|url=http://www.mgs.md.gov/seismic/education/no3.pdf|url-status=dead|archive-url=https://web.archive.org/web/20161221093605/http://www.mgs.md.gov/seismic/education/no3.pdf|archive-date=December 21, 2016}}</ref> On the other hand, earthquakes of magnitude ≥8.0 occur about once a year, on average.<ref name="IRIS" /> The largest recorded earthquake was the [[1960 Valdivia earthquake|Great Chilean earthquake]] of May 22, 1960, which had a magnitude of 9.5 on the [[moment magnitude scale]].<ref>{{cite web |url=https://earthquake.usgs.gov/regional/world/10_largest_world.php |title=Largest Earthquakes in the World Since 1900 |date=November 30, 2012 |access-date=December 18, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20091007163455/http://earthquake.usgs.gov/regional/world/10_largest_world.php |archive-date=October 7, 2009 }}</ref> |
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Seismologist Susan Hough has suggested that 10 may represent a very approximate upper limit, |
Seismologist Susan Hough has suggested that a magnitude 10 quake may represent a very approximate upper limit for what the Earth's tectonic zones are capable of, which would be the result of the largest known continuous belt of faults rupturing together (along the Pacific coast of the Americas).<ref>{{cite book|last1=Silver|first1=Nate|title=The signal and the noise : the art and science of prediction|date=2013|publisher=Penguin|location=London|isbn=9780141975658}}</ref> A research at the [[Tohoku University]] in Japan found that a magnitude 10 earthquake was theoretically possible if a combined {{convert|3000|km|mi}} of faults from the [[Japan Trench]] to the [[Kuril–Kamchatka Trench]] ruptured together and moved by {{convert|60|m|ft}} (or if a similar large-scale rupture occurred elsewhere). Such an earthquake would cause ground motions for up to an hour, with tsunamis hitting shores while the ground is still shaking, and if this kind of earthquake occurred, it would probably be a 1-in-10,000-year event.<ref name="Magnitude 10 tremblor">{{cite web|url=https://www.japantimes.co.jp/news/2012/12/15/national/magnitude-10-temblor-could-happen-study/|title=Magnitude 10 temblor could happen: study|author=Kyodo|work=The Japan Times|date=December 15, 2012|access-date=September 15, 2020}}</ref> |
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== Development == |
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[[File:CharlesRichter.jpg|thumb|upright|[[Charles Francis Richter]] (circa 1970)]] |
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Prior to the development of the magnitude scale, the only measure of an earthquake's strength or "size" was a subjective assessment of the intensity of shaking observed near the [[epicenter]] of the earthquake, categorized by various [[seismic intensity scales]] such as the [[Rossi–Forel scale]]. ("Size" is used in the sense of the quantity of energy released, not the size of the area affected by shaking, though higher-energy earthquakes do tend to affect a wider area, depending on the local geology.) In 1883, [[John Milne]] surmised that the shaking of large earthquakes might generate waves detectable around the globe, and in 1899 E. Von Rehbur Paschvitz observed in Germany seismic waves attributable to an earthquake in [[Tokyo]].<ref>{{Harvnb|Bolt|1993|p=47}}.</ref> In the 1920s, [[Harry O. Wood]] and [[John August Anderson|John A. Anderson]] developed the [[Wood–Anderson seismograph]], one of the first practical instruments for recording seismic waves.<ref>{{Harvnb|Hough|2007|p=}};</ref> Wood then built, under the auspices of the [[California Institute of Technology]] and the [[Carnegie Institution for Science|Carnegie Institute]], a network of seismographs stretching across [[Southern California]].<ref>{{Harvnb|Hough|2007|p=57}}.</ref> He also recruited the young and unknown Charles Richter to measure the seismograms and locate the earthquakes generating the seismic waves.<ref>{{Harvnb|Hough|2007|pp=57, 116}}.</ref> |
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In 1931, [[Kiyoo Wadati]] showed how he had measured, for several strong earthquakes in Japan, the amplitude of the shaking observed at various distances from the epicenter. He then plotted the logarithm of the amplitude against the distance and found a series of curves that showed a rough correlation with the estimated magnitudes of the earthquakes.<ref>{{Harvnb|Richter|1935|p=2}}.</ref> Richter resolved some difficulties with this method<ref>{{Harvnb|Richter|1935|pp=1–5}}.</ref> and then, using data collected by his colleague [[Beno Gutenberg]], he produced similar curves, confirming that they could be used to compare the relative magnitudes of different earthquakes.<ref>{{Harvnb|Richter|1935|pp=2–3}}.</ref> |
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Additional developments were required to produce a practical method of assigning an absolute measure of magnitude. First, to span the wide range of possible values, Richter adopted Gutenberg's suggestion of a [[logarithm]]ic scale, where each step represents a tenfold increase of magnitude, similar to the magnitude scale used by astronomers [[Apparent magnitude|for star brightness]].<ref>[pending]</ref> Second, he wanted a magnitude of zero to be around the limit of human perceptibility.<ref>{{Harvnb|Richter|1935|p=14}}: {{Harvnb|Gutenberg|Richter|1936|p=183}}.</ref> Third, he specified the Wood–Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in [[microns]]", measured at a distance of {{Convert|100|km|mi|abbr=on}}. The scale was calibrated by defining a magnitude 0 shock as one that produces (at a distance of {{Convert|100|km|mi|abbr=on}}) a maximum amplitude of 1 micron (1 μm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismometer.<ref>{{Harvnb|Richter|1935|p=5}}. See also {{Harvnb|Hutton|Boore|1987|p=1}}; {{Harvnb|Chung|Bernreuter|1980|p=10}}.</ref> Finally, Richter calculated a table of distance corrections,<ref>{{Harvnb|Richter|1935|p=6}}, Table I.</ref> in that for distances less than 200 kilometers<ref>{{Harvnb|Richter|1935|p=32}}.</ref> the attenuation is strongly affected by the structure and properties of the regional geology.<ref>{{Harvnb|Chung|Bernreuter|1980|p=5}}.</ref> |
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When Richter presented the resulting scale in 1935, he called it (at the suggestion of Harry Wood) simply a "magnitude" scale.<ref>{{Harvnb|Richter|1935|p=1}}. His article is titled: "An Instrumental Earthquake Magnitude Scale".</ref> "Richter magnitude" appears to have originated when [[Perry Byerly]] told the press that the scale was Richter's and "should be referred to as such."<ref>{{Harvnb|Hough|2007|pp=123–124}}.</ref> In 1956, Gutenberg and Richter, while still referring to "magnitude scale", labelled it "local magnitude", with the symbol {{M|L}}, to distinguish it from two other scales they had developed, the [[surface-wave magnitude]] (M<sub>S</sub>) and [[body wave magnitude]] (M<sub>B</sub>)<!-- These are non-standard: do not use the "M" template here. --> scales.<ref name="ReferenceA"/> |
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==Details== |
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[[File:How-the-Richter-Magnitude-Scale-is-determined.jpg|thumb|How Richter magnitude is determined – the larger the value on the log graph, the higher the damage caused.]] |
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The Richter scale was defined in 1935 for particular circumstances and instruments; the particular circumstances refer to it being defined for Southern California and "implicitly incorporates the [[attenuation|attenuative]] properties of Southern California crust and mantle."<ref>{{cite web |url=https://earthquake.usgs.gov/earthquakes/eqarchives/mineblast/definitions.php |title=Explanation of Bulletin Listings, USGS}}</ref> The particular instrument used would become saturated by strong earthquakes and unable to record high values. The scale was replaced in the 1970s by the [[moment magnitude scale]] (MMS, symbol {{M|w}}); for earthquakes adequately measured by the Richter scale, numerical values are approximately the same. Although values measured for earthquakes now are {{M|w}}, they are frequently reported by the press as Richter values, even for earthquakes of magnitude over 8, when the Richter scale becomes meaningless. |
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The Richter and MMS scales measure the energy released by an earthquake; another scale, the [[Mercalli intensity scale]], classifies earthquakes by their ''effects'', from detectable by instruments but not noticeable, to catastrophic. The energy and effects are not necessarily strongly correlated; a shallow earthquake in a populated area with soil of certain types can be far more intense in impact than a much more energetic deep earthquake in an isolated area. |
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Several scales have been historically described as the "Richter scale",{{citation needed|date=January 2020}}, especially the ''local magnitude'' {{M|L}} and the surface wave {{M|s}} scale. In addition, the ''body wave magnitude'', {{M|b}}, and the ''moment magnitude'', {{M|w}}, abbreviated MMS, have been widely used for decades. A couple of new techniques to measure magnitude are in the development stage by seismologists. |
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All magnitude scales have been designed to give numerically similar results. This goal has been achieved well for {{M|L}}, {{M|s}}, and {{M|w}}.<ref>{{Harvnb|Richter|1935}}.</ref><ref>Richter, C.F., "Elementary Seismology", ed, Vol., W. H. Freeman and Co., San Francisco, 1956.</ref> The {{M|b}} scale gives somewhat different values than the other scales. The reason for so many different ways to measure the same thing is that at different distances, for different [[hypocenter|hypocentral]] depths, and for different earthquake sizes, the amplitudes of different types of elastic waves must be measured. |
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{{M|L}} is the scale used for the majority of earthquakes reported (tens of thousands) by local and regional seismological observatories. For large earthquakes worldwide, the moment magnitude scale (MMS) is most common, although {{M|s}} is also reported frequently. |
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The [[seismic moment]], '''''{{M|0}}''''', is proportional to the area of the rupture times the average slip that took place in the earthquake, thus it measures the physical size of the event. {{M|w}} is derived from it empirically as a quantity without units, just a number designed to conform to the {{M|s}} scale.<ref>{{cite journal | last1 = Hanks | first1 = T. C. | last2 = Kanamori | first2 = H. | year = 1979 | title = Moment magnitude scale | journal = Journal of Geophysical Research | volume = 84 | issue = B5| page = 2348 | doi=10.1029/jb084ib05p02348 | bibcode = 1979JGR....84.2348H}}</ref> A spectral analysis is required to obtain {{M|0}}. In contrast, the other magnitudes are derived from a simple measurement of the amplitude of a precisely defined wave. |
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All scales, except {{M|w}}, saturate for large earthquakes, meaning they are based on the amplitudes of waves that have a wavelength shorter than the rupture length of the earthquakes. These short waves (high-frequency waves) are too short a yardstick to measure the extent of the event. The resulting effective upper limit of measurement for {{M|L}} is about 7 and about 8.5<ref>{{cite web |url=http://www.weather.gov.hk/education/edu02rga/article/ele-EarthquakeMagnetude_e.htm |title=On Earthquake Magnitudes |first=Wang-chun |last=Woo |date=September 2012 |publisher=Hong Kong Observatory |access-date=December 18, 2013 |archive-date=May 24, 2017 |archive-url=https://web.archive.org/web/20170524163729/http://www.weather.gov.hk/education/edu02rga/article/ele-EarthquakeMagnetude_e.htm |url-status=dead }}</ref> for {{M|s}}.<ref name="Local magnitude">{{cite web |url=https://earthquake.usgs.gov/hazards/qfaults/glossary.php |title=Richter scale |work=Glossary |publisher=United States Geological Survey |date=March 31, 2010 }}</ref> |
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New techniques to avoid the saturation problem and to measure magnitudes rapidly for very large earthquakes are being developed. One of these is based on the long-period P-wave;<ref>Di Giacomo, D., Parolai, S., Saul, J., Grosser, H., Bormann, P., Wang, R. & Zschau, J., 2008. "Rapid determination of the energy magnitude Me," in ''European Seismological Commission 31st General Assembly,'' Hersonissos.</ref> The other is based on a recently discovered channel wave.<ref>Rivera, L. & Kanamori, H., 2008. "Rapid source inversion of W phase for tsunami warning," in ''European Geophysical Union General Assembly,'' pp. A-06228, Vienna.</ref> |
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The [[energy]] release of an earthquake,<ref>{{cite journal | last1 = Vassiliou | first1 = Marius | last2 = Kanamori | first2 = Hiroo | year = 1982 | title = The Energy Release in Earthquakes | journal = Bull. Seismol. Soc. Am. | volume = 72 | pages = 371–387 }}</ref> which closely correlates to its destructive power, scales with the {{frac|3|2}} power of the shaking amplitude (see [[Moment magnitude scale]] for an explanation). Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 (<math>=({10^{1.0}})^{(3/2)}</math>) in the energy released; a difference in magnitude of 2.0 is equivalent to a factor of 1000 (<math>=({10^{2.0}})^{(3/2)}</math>) in the energy released.<ref>{{cite journal |first=William |last=Spence |first2=Stuart A. |last2=Sipkin |first3=George L. |last3=Choy |url=https://earthquake.usgs.gov/learn/topics/measure.php |title=Measuring the Size of an Earthquake |journal=Earthquakes and Volcanoes |volume=21 |number=1 |year=1989}}</ref> The elastic energy radiated is best derived from an integration of the radiated spectrum, but an estimate can be based on {{M|b}} because most energy is carried by the high-frequency waves. |
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==Magnitude empirical formulae== |
==Magnitude empirical formulae== |
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These formulae for Richter magnitude <math>\ |
These formulae for Richter magnitude <math>\ M_\mathsf{L}\ </math> are alternatives to using Richter correlation tables based on Richter standard seismic event <math>\big(\ M_\mathsf{L} = 0\ ,</math> <math>\ A = 0.001\ \mathsf{mm}\ ,</math> <math>\ D=100\ \mathsf{km}\ \big) ~.</math> In the formulas below, <math>\ \Delta\ </math> is the epicentral distance in [[kilometer]]s, and <math>\ \Delta^{\circ}\ </math> is the same distance represented as sea level [[great circle]] degrees. |
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The Lillie empirical formula: |
The '''Lillie empirical formula''' is: |
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:<math>M_\ |
:<math>\ M_\mathsf{L} = \log_{10} A - 2.48 + 2.76\ \log_{10} \Delta\ </math> |
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: where <math>\ A\ </math> is the amplitude (maximum ground displacement) of the [[P wave]], in [[micrometre|micrometers (μm)]], measured at 0.8 Hz. |
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'''Lahr's empirical formula'''<ref name=Lahr>{{cite report |last=Lahr |first=J.C. |year=1980 |title=HYPOELLIPSE: A computer program for determining local earthquake hypocentral parameters, magnitude, and first-motion pattern |journal=US Geological Survey open-file report |volume=80-59 }}</ref> proposal is: |
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For distances <math>D</math> less than 200 km, |
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:<math>M_\ |
:<math>\ M_\mathsf{L} = \log_{10} A + 1.6\ \log_{10} D - 0.15\ ,</math> |
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: where |
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and for distances between 200 km and 600 km, |
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:: <math>\ A\ </math> is [[seismograph]] signal amplitude in [[millimetre|mm]] and |
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:<math>M_\mathrm{L} = \log_{10} A + 3.0\log_{10} D - 3.38,</math> |
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:: <math>\ D\ </math> is in [[kilometre|km]], for distances under 200 km . |
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and |
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: <math>\ M_\mathsf{L} = \log_{10} A + 3.0\ \log_{10} D - 3.38\ ;</math> |
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: where <math>\ D\ </math> is in [[kilometre|km]], for distances between 200 km and 600 km . |
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The Bisztricsany |
The '''Bisztricsany empirical formula''' (1958) for epicentre distances between 4° and 160° is:<ref name=al-Arifi>{{cite journal |last1=al-Arifi |first1=Nassir S. |last2=al-Humidan |first2=Saad |date=July 2012 |title=Local and regional earthquake magnitude calibration of Tabuk analog sub-network, Northwest of Saudi Arabia |journal=Journal of King Saud University – Science |volume=24 |issue=3 |pages=257–263 |doi=10.1016/j.jksus.2011.04.001 |doi-access=free}}</ref> |
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:<math>M_\ |
: <math>\ M_\mathsf{L} = 2.92 + 2.25\ \log_{10} \left( \tau \right) - 0.001\ \Delta^{\circ}\ ,</math> |
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: where |
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Where <math>\tau</math> is the duration of the surface wave in seconds, and <math>\Delta</math> is in degrees. <math>M_\mathrm{L}</math> is mainly between 5 and 8. |
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:: <math>\ \tau\ </math> is the duration of the surface wave in seconds, and |
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:: <math>\ \Delta^{\circ}\ </math> is in degrees. |
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:: <math>\ M_\mathsf{L}\ </math> is mainly between 5 and 8. |
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The '''Tsumura empirical formula''' is:<ref name="Al-Arifi">{{cite journal|last1=Al-Arifi|first1=Nassir S.|last2=Al-Humidan|first2=Saad|title=Local and regional earthquake magnitude calibration of Tabuk analog sub-network, Northwest of Saudi Arabia|journal=Journal of King Saud University – Science|date=July 2012|volume=24|issue=3|pages=257–263|doi=10.1016/j.jksus.2011.04.001|doi-access=free}}</ref> |
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The Tsumura empirical formula:<ref name="Al-Arifi"/> |
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:<math>M_\ |
: <math>\ M_\mathsf{L} = -2.53 + 2.85 \log_{10} \left(F - P\right) + 0.0014\ \Delta^{\circ}\ ,</math> |
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: where |
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Where <math>F-P</math> is the total duration of oscillation in seconds. <math>M_\mathrm{L}</math> is mainly between 3 and 5. |
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:: <math>\ F - P\ </math> is the total duration of oscillation in seconds. |
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:: <math>\ M_\mathsf{L}\ </math> mainly takes on values between 3 and 5. |
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The Tsuboi |
The '''Tsuboi''' (University of Tokyo) '''empirical formula''' is: |
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:<math>M_\ |
:<math>\ M_\mathsf{L} = \log_{10} A + 1.73\ \log_{10} \Delta - 0.83\ ,</math> |
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: where <math>\ A\ </math> is the amplitude in [[micrometre|μm]]. |
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==See also== |
==See also== |
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{{Portal|Earth sciences}} |
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{{portal|Earthquakes}} |
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{{div col|colwidth=30em}} |
{{div col|colwidth=30em}} |
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* [[1935 in science]] |
* [[1935 in science]] |
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* [[Moment magnitude scale]] |
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* [[Rohn Emergency Scale]] for measuring the magnitude (intensity) of any emergency |
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* [[Seismic intensity scales]] |
* [[Seismic intensity scales]] |
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* [[Seismic magnitude scales]] |
* [[Seismic magnitude scales]] |
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* [[Timeline of United States inventions (1890–1945)#Great Depression and World War II (1929–1945)]] |
* [[Timeline of United States inventions (1890–1945)#Great Depression and World War II (1929–1945)|Timeline of United States inventions (1890–1945)]] |
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{{div col end}} |
{{div col end}} |
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==Notes== |
==Notes== |
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{{Reflist |
{{Reflist}} |
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==Sources== |
==Sources== |
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{{bots|deny=Citation bot, BattyBot, BG19bot}} |
{{bots|deny=Citation bot, BattyBot, BG19bot}} |
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*{{Citation |
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|last1= Bolt |first1= B. A. |
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|year= 1993 |
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|title= Earthquakes and geological discovery |
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*{{Citation |last=Hough |first=S. E. |year=2007 |title=Richter's scale: measure of an earthquake, measure of a man |publisher=Princeton University Press |isbn=978-0-691-12807-8 |url=https://books.google.com/books?id=rvmDeAxEiO8C}}. |
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|isbn= 0-7167-5040-6 |
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*{{Citation |first1=Hiroo |last1=Kanamori |date=February 2, 1978 |title=Quantification of Earthquakes |journal=Nature |volume=271 |issue=5644 |pages=411–414 |doi=10.1038/271411a0 |url=http://gps-prod-storage.cloud.caltech.edu.s3.amazonaws.com/people_personal_assets/kanamori/HKnat78.pdf |bibcode=1978Natur.271..411K}}. |
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}}. |
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*{{Citation |first1=C. F. |last1=Richter |author-link=Charles F. Richter |date=January 1935 |title=An Instrumental Earthquake Magnitude Scale |journal=Bulletin of the Seismological Society of America |volume=25 |issue=1 |pages=1–32 |url=http://authors.library.caltech.edu/47921/1/1.full%20(1).pdf |access-date=March 14, 2018 |archive-date=July 10, 2018 |archive-url=https://web.archive.org/web/20180710125050/https://authors.library.caltech.edu/47921/1/1.full%20(1).pdf |url-status=dead}}. |
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*{{Citation |
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|first1= D. M. |last1= Boore |
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|date= September 1989 |
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|title= The Richter scale: its development and use for determining earthquake source parameter |
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|journal= Tectonophysics |
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|volume= 166 |issue= 1-3 |pages= 1–14 |
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|doi= |
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|url= http://w.daveboore.com/pubs_online/richter_scale_tectonophysics_1989.pdf |
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}} |
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*{{Citation |
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|first1= D. H. |last1= Chung |
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|first2= D. L. |last2= Bernreuter |
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|date= 1980 |
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|title= Regional Relationships Among Earthquake Magnitude Scales. |
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|url= https://www.osti.gov/scitech/servlets/purl/5073993/ |
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}}, NUREG/CR-1457. |
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*{{Citation |
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|first1= B. |last1= Gutenberg |
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|first2= C. F. |last2= Richter |
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|date= 21 February 1936 |
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|title= Discussion: Magnitude and energy of earthquakes |
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|journal= Science |
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|volume= 83 |issue= 2147 |pages= 183–185 |
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|doi= 10.1126/science.83.2147.183 |
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|url= http://science.sciencemag.org/content/sci/83/2147/183.full.pdf |
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}}. |
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*{{Citation |
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|last1= Gutenberg |first1= B. |
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|last2= Richter |first2= C. F. |
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|year= 1956b |
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|title= Earthquake magnitude, intensity, energy, and acceleration (Second Paper) |
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|journal= Bulletin of the Seismological Society of America |
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|volume= 46 |issue= 2 |pages= 105–145 |
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}}. |
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*{{Citation |
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|last= Hough |first= S. E. |
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|year=2007 |
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|title= Richter's scale: measure of an earthquake, measure of a man |
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|publisher=Princeton University Press |
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|isbn=978-0-691-12807-8 |
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|url=https://books.google.com/books?id=rvmDeAxEiO8C |
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}}. |
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*{{Citation |
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|first1= L. K. |last1= Hutton |
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|first2= David M. |last2= Boore |
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|date= December 1987 |
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|title= The ''M''<sub>L</sub> scale in Southern California |
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|journal= Nature |
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|volume= 271 |issue= |pages= 411–414 |
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|doi= 10.1038/271411a0 |
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|url= http://gps-prod-storage.cloud.caltech.edu.s3.amazonaws.com/people_personal_assets/kanamori/HKnat78.pdf |
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}}. |
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*{{Citation |
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|first1= C. F. |last1= Richter |
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|author-link = Charles F. Richter |
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|date= January 1935 |
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|title= An Instrumental Earthquake Magnitude Scale |
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|journal= Bulletin of the Seismological Society of America |
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|volume= 25 |issue= 1 |pages= 1–32 |
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|url= http://authors.library.caltech.edu/47921/1/1.full%20(1).pdf |
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}}. |
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{{refend}} {{div col end}} |
{{refend}} {{div col end}} |
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==External links== |
==External links== |
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* {{britannica|502877|Richter scale (seismology)}} |
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* [http://www.iris.edu/seismon/ Seismic Monitor] – [[IRIS Consortium]] |
* [http://www.iris.edu/seismon/ Seismic Monitor] – [[IRIS Consortium]] |
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* [https://web.archive.org/web/20160504144754/http://earthquake.usgs.gov/aboutus/docs/020204mag_policy.php USGS Earthquake Magnitude Policy (implemented on January 18, 2002)] – USGS |
* [https://web.archive.org/web/20160504144754/http://earthquake.usgs.gov/aboutus/docs/020204mag_policy.php USGS Earthquake Magnitude Policy (implemented on January 18, 2002)] – USGS |
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Latest revision as of 03:41, 6 December 2024
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Earthquakes |
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The Richter scale[1] (/ˈrɪktər/), also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale,[2] is a measure of the strength of earthquakes, developed by Charles Richter in collaboration with Beno Gutenberg, and presented in Richter's landmark 1935 paper, where he called it the "magnitude scale".[3] This was later revised and renamed the local magnitude scale, denoted as ML or ML .[4]
Because of various shortcomings of the original ML scale, most seismological authorities now use other similar scales such as the moment magnitude scale (Mw ) to report earthquake magnitudes, but much of the news media still erroneously refers to these as "Richter" magnitudes. All magnitude scales retain the logarithmic character of the original and are scaled to have roughly comparable numeric values (typically in the middle of the scale). Due to the variance in earthquakes, it is essential to understand the Richter scale uses common logarithms simply to make the measurements manageable (i.e., a magnitude 3 quake factors 10³ while a magnitude 5 quake factors 105 and has seismometer readings 100 times larger).[5]
Richter magnitudes
[edit]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. The original formula is:[6]
where A is the maximum excursion of the Wood-Anderson seismograph, the empirical function A0 depends only on the epicentral distance of the station, . In practice, readings from all observing stations are averaged after adjustment with station-specific corrections to obtain the ML value.[6]
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, and each increase of 0.2 corresponds to approximately a doubling of the energy released.
Events with magnitudes greater than 4.5 are strong enough to be recorded by a seismograph anywhere in the world, so long as its sensors are not located in the earthquake's shadow.[7][8][9]
The following describes the typical effects of earthquakes of various magnitudes near the epicenter.[10] The values are typical and may not be exact in a future event because intensity and ground effects depend not only on the magnitude but also on (1) the distance to the epicenter, (2) the depth of the earthquake's focus beneath the epicenter, (3) the location of the epicenter, and (4) geological conditions.
Magnitude | Description | Typical maximum modified Mercalli intensity[11] | Average earthquake effects | Average frequency of occurrence globally (estimated) |
---|---|---|---|---|
1.0–1.9 | Micro | I | Microearthquakes, not felt. Recorded by seismographs.[12] | Continual/several million per year |
2.0–2.9 | Minor | I | Felt slightly by some people. No damage to buildings. | Over one million per year |
3.0–3.9 | Slight | II to III | Often felt by people, but very rarely causes damage. Shaking of indoor objects can be noticeable. | Over 100,000 per year |
4.0–4.9 | Light | IV to V | Noticeable shaking of indoor objects and rattling noises. Felt by most people in the affected area. Slightly felt outside. Generally causes zero to minimal damage. Moderate to significant damage is very unlikely. Some objects may fall off shelves or be knocked over. | 10,000 to 15,000 per year |
5.0–5.9 | Moderate | VI to VII | Can cause damage of varying severity to poorly constructed buildings. Zero to slight damage to all other buildings. Felt by everyone. | 1,000 to 1,500 per year |
6.0–6.9 | Strong | VII to IX | Damage to a moderate number of well-built structures in populated areas. Earthquake-resistant structures survive with slight to moderate damage. Poorly designed structures receive moderate to severe damage. Felt in wider areas; up to hundreds of kilometers from the epicenter. Strong to violent shaking in the epicentral area. | 100 to 150 per year |
7.0–7.9 | Major | VIII or higher | Causes damage to most buildings, some to partially or completely collapse or receive severe damage. Well-designed structures are likely to receive damage. Felt across great distances with major damage mostly limited to 250 km from the epicenter. | 10 to 20 per year |
8.0–8.9 | Great | Major damage to buildings, and structures likely to be destroyed. Will cause moderate to heavy damage to sturdy or earthquake-resistant buildings. Damaging in large areas. Felt in extremely large regions. | One per year | |
9.0–9.9 | Extreme | Near total destruction – severe damage or collapse to all buildings. Heavy damage and shaking extend to distant locations. Permanent changes in ground topography. | One to three per century[13] |
(Based on U.S. Geological Survey documents.)[14]
The intensity and death toll depend on several factors (earthquake depth, epicenter location, and population density, to name a few) and can vary widely.
Millions of minor earthquakes occur every year worldwide, equating to hundreds every hour every day.[15] On the other hand, earthquakes of magnitude ≥8.0 occur about once a year, on average.[15] The largest recorded earthquake was the Great Chilean earthquake of May 22, 1960, which had a magnitude of 9.5 on the moment magnitude scale.[16]
Seismologist Susan Hough has suggested that a magnitude 10 quake may represent a very approximate upper limit for what the Earth's tectonic zones are capable of, which would be the result of the largest known continuous belt of faults rupturing together (along the Pacific coast of the Americas).[17] A research at the Tohoku University in Japan found that a magnitude 10 earthquake was theoretically possible if a combined 3,000 kilometres (1,900 mi) of faults from the Japan Trench to the Kuril–Kamchatka Trench ruptured together and moved by 60 metres (200 ft) (or if a similar large-scale rupture occurred elsewhere). Such an earthquake would cause ground motions for up to an hour, with tsunamis hitting shores while the ground is still shaking, and if this kind of earthquake occurred, it would probably be a 1-in-10,000-year event.[18]
Development
[edit]Prior to the development of the magnitude scale, the only measure of an earthquake's strength or "size" was a subjective assessment of the intensity of shaking observed near the epicenter of the earthquake, categorized by various seismic intensity scales such as the Rossi–Forel scale. ("Size" is used in the sense of the quantity of energy released, not the size of the area affected by shaking, though higher-energy earthquakes do tend to affect a wider area, depending on the local geology.) In 1883, John Milne surmised that the shaking of large earthquakes might generate waves detectable around the globe, and in 1899 E. Von Rehbur Paschvitz observed in Germany seismic waves attributable to an earthquake in Tokyo.[19] In the 1920s, Harry O. Wood and John A. Anderson developed the Wood–Anderson seismograph, one of the first practical instruments for recording seismic waves.[20] Wood then built, under the auspices of the California Institute of Technology and the Carnegie Institute, a network of seismographs stretching across Southern California.[21] He also recruited the young and unknown Charles Richter to measure the seismograms and locate the earthquakes generating the seismic waves.[22]
In 1931, Kiyoo Wadati showed how he had measured, for several strong earthquakes in Japan, the amplitude of the shaking observed at various distances from the epicenter. He then plotted the logarithm of the amplitude against the distance and found a series of curves that showed a rough correlation with the estimated magnitudes of the earthquakes.[23] Richter resolved some difficulties with this method[24] and then, using data collected by his colleague Beno Gutenberg, he produced similar curves, confirming that they could be used to compare the relative magnitudes of different earthquakes.[25]
Additional developments were required to produce a practical method of assigning an absolute measure of magnitude. First, to span the wide range of possible values, Richter adopted Gutenberg's suggestion of a logarithmic scale, where each step represents a tenfold increase of magnitude, similar to the magnitude scale used by astronomers for star brightness.[26] Second, he wanted a magnitude of zero to be around the limit of human perceptibility.[27] Third, he specified the Wood–Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in microns", measured at a distance of 100 km (62 mi). The scale was calibrated by defining a magnitude 0 shock as one that produces (at a distance of 100 km (62 mi)) a maximum amplitude of 1 micron (1 μm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismometer.[28] Finally, Richter calculated a table of distance corrections,[29] in that for distances less than 200 kilometers[30] the attenuation is strongly affected by the structure and properties of the regional geology.[31]
When Richter presented the resulting scale in 1935, he called it (at the suggestion of Harry Wood) simply a "magnitude" scale.[32] "Richter magnitude" appears to have originated when Perry Byerly told the press that the scale was Richter's and "should be referred to as such."[33] In 1956, Gutenberg and Richter, while still referring to "magnitude scale", labelled it "local magnitude", with the symbol ML , to distinguish it from two other scales they had developed, the surface-wave magnitude (MS) and body wave magnitude (MB) scales.[4]
Details
[edit]The Richter scale was defined in 1935 for particular circumstances and instruments; the particular circumstances refer to it being defined for Southern California and "implicitly incorporates the attenuative properties of Southern California crust and mantle."[34] The particular instrument used would become saturated by strong earthquakes and unable to record high values. The scale was replaced in the 1970s by the moment magnitude scale (MMS, symbol Mw ); for earthquakes adequately measured by the Richter scale, numerical values are approximately the same. Although values measured for earthquakes now are Mw , they are frequently reported by the press as Richter values, even for earthquakes of magnitude over 8, when the Richter scale becomes meaningless.
The Richter and MMS scales measure the energy released by an earthquake; another scale, the Mercalli intensity scale, classifies earthquakes by their effects, from detectable by instruments but not noticeable, to catastrophic. The energy and effects are not necessarily strongly correlated; a shallow earthquake in a populated area with soil of certain types can be far more intense in impact than a much more energetic deep earthquake in an isolated area.
Several scales have been historically described as the "Richter scale",[citation needed], especially the local magnitude ML and the surface wave Ms scale. In addition, the body wave magnitude, mb , and the moment magnitude, Mw , abbreviated MMS, have been widely used for decades. A couple of new techniques to measure magnitude are in the development stage by seismologists.
All magnitude scales have been designed to give numerically similar results. This goal has been achieved well for ML , Ms , and Mw .[35][36] The mb scale gives somewhat different values than the other scales. The reason for so many different ways to measure the same thing is that at different distances, for different hypocentral depths, and for different earthquake sizes, the amplitudes of different types of elastic waves must be measured.
ML is the scale used for the majority of earthquakes reported (tens of thousands) by local and regional seismological observatories. For large earthquakes worldwide, the moment magnitude scale (MMS) is most common, although Ms is also reported frequently.
The seismic moment, M0 , is proportional to the area of the rupture times the average slip that took place in the earthquake, thus it measures the physical size of the event. Mw is derived from it empirically as a quantity without units, just a number designed to conform to the Ms scale.[37] A spectral analysis is required to obtain M0 . In contrast, the other magnitudes are derived from a simple measurement of the amplitude of a precisely defined wave.
All scales, except Mw , saturate for large earthquakes, meaning they are based on the amplitudes of waves that have a wavelength shorter than the rupture length of the earthquakes. These short waves (high-frequency waves) are too short a yardstick to measure the extent of the event. The resulting effective upper limit of measurement for ML is about 7 and about 8.5[38] for Ms .[39]
New techniques to avoid the saturation problem and to measure magnitudes rapidly for very large earthquakes are being developed. One of these is based on the long-period P-wave;[40] The other is based on a recently discovered channel wave.[41]
The energy release of an earthquake,[42] which closely correlates to its destructive power, scales with the 3⁄2 power of the shaking amplitude (see Moment magnitude scale for an explanation). Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 () in the energy released; a difference in magnitude of 2.0 is equivalent to a factor of 1000 () in the energy released.[43] The elastic energy radiated is best derived from an integration of the radiated spectrum, but an estimate can be based on mb because most energy is carried by the high-frequency waves.
Magnitude empirical formulae
[edit]These formulae for Richter magnitude are alternatives to using Richter correlation tables based on Richter standard seismic event In the formulas below, is the epicentral distance in kilometers, and is the same distance represented as sea level great circle degrees.
The Lillie empirical formula is:
- where is the amplitude (maximum ground displacement) of the P wave, in micrometers (μm), measured at 0.8 Hz.
Lahr's empirical formula[44] proposal is:
- where
- is seismograph signal amplitude in mm and
- is in km, for distances under 200 km .
and
- where is in km, for distances between 200 km and 600 km .
The Bisztricsany empirical formula (1958) for epicentre distances between 4° and 160° is:[45]
- where
- is the duration of the surface wave in seconds, and
- is in degrees.
- is mainly between 5 and 8.
The Tsumura empirical formula is:[46]
- where
- is the total duration of oscillation in seconds.
- mainly takes on values between 3 and 5.
The Tsuboi (University of Tokyo) empirical formula is:
- where is the amplitude in μm.
See also
[edit]Notes
[edit]- ^ Kanamori 1978, p. 411. Hough (2007, pp. 122–126) discusses the name at some length.
- ^ McPhee, John (1998). Annals of the Former World. Farrar, Straus and Giroux. p. 608.
- ^ Kanamori 1978, p. 411; Richter 1935.
- ^ a b Gutenberg & Richter 1956b, p. 30.
- ^ "Discovery Project 17: Orders of Magnitude". stewartmath.com. Retrieved February 24, 2022.
- ^ a b Ellsworth, William L. (1991). "The Richter Scale ML". In Wallace, Robert E. (ed.). The San Andreas Fault System, California. United States Geological Survey. p. 177. Professional Paper 1515. Archived from the original on April 25, 2016. Retrieved September 14, 2008.
- ^ Brush, Stephen G. (September 1980). "Discovery of the Earth's core". American Journal of Physics. 48 (9): 705–724. doi:10.1119/1.12026. ISSN 0002-9505.
- ^ Michael Allaby (2008). A dictionary of earth sciences (3rd ed.). Oxford. ISBN 978-0-19-921194-4. OCLC 177509121.
{{cite book}}
: CS1 maint: location missing publisher (link) - ^ Einarsson, P. (September 1978). "S-wave shadows in the Krafla Caldera in NE-Iceland, evidence for a magma chamber in the crust". Bulletin Volcanologique. 41 (3): 187–195. doi:10.1007/bf02597222. hdl:20.500.11815/4200. ISSN 0258-8900.
- ^ "What is the Richter Magnitude Scale?". GNS Science. Archived from the original on August 3, 2021. Retrieved August 3, 2021.
- ^ "Magnitude / Intensity Comparison". Archived from the original on June 23, 2011.
- ^ This is what Richter wrote in his Elementary Seismology (1958), an opinion copiously reproduced afterward in Earth's science primers. Recent evidence shows that earthquakes with negative magnitudes (down to −0.7) can also be felt in exceptional cases, especially when the focus is very shallow (a few hundred meters). See: Thouvenot, F.; Bouchon, M. (2008). "What is the lowest magnitude threshold at which an earthquake can be felt or heard, or objects thrown into the air?," in Fréchet, J., Meghraoui, M. & Stucchi, M. (eds), Modern Approaches in Solid Earth Sciences (vol. 2), Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes, Springer, Dordrecht, 313–326.
- ^ McCaffrey, R. (2008). "Global frequency of magnitude 9 earthquakes". Geology. 36 (3): 263–266. doi:10.1130/G24402A.1.
- ^ "Earthquake Facts and Statistics". United States Geological Survey. November 29, 2012. Archived from the original on May 24, 2010. Retrieved December 18, 2013.
- ^ a b "How Often Do Earthquakes Occur" (PDF). Archived from the original (PDF) on December 21, 2016.
- ^ "Largest Earthquakes in the World Since 1900". November 30, 2012. Archived from the original on October 7, 2009. Retrieved December 18, 2013.
- ^ Silver, Nate (2013). The signal and the noise : the art and science of prediction. London: Penguin. ISBN 9780141975658.
- ^ Kyodo (December 15, 2012). "Magnitude 10 temblor could happen: study". The Japan Times. Retrieved September 15, 2020.
- ^ Bolt 1993, p. 47.
- ^ Hough 2007;
- ^ Hough 2007, p. 57.
- ^ Hough 2007, pp. 57, 116.
- ^ Richter 1935, p. 2.
- ^ Richter 1935, pp. 1–5.
- ^ Richter 1935, pp. 2–3.
- ^ [pending]
- ^ Richter 1935, p. 14: Gutenberg & Richter 1936, p. 183.
- ^ Richter 1935, p. 5. See also Hutton & Boore 1987, p. 1; Chung & Bernreuter 1980, p. 10.
- ^ Richter 1935, p. 6, Table I.
- ^ Richter 1935, p. 32.
- ^ Chung & Bernreuter 1980, p. 5.
- ^ Richter 1935, p. 1. His article is titled: "An Instrumental Earthquake Magnitude Scale".
- ^ Hough 2007, pp. 123–124.
- ^ "Explanation of Bulletin Listings, USGS".
- ^ Richter 1935.
- ^ Richter, C.F., "Elementary Seismology", ed, Vol., W. H. Freeman and Co., San Francisco, 1956.
- ^ Hanks, T. C.; Kanamori, H. (1979). "Moment magnitude scale". Journal of Geophysical Research. 84 (B5): 2348. Bibcode:1979JGR....84.2348H. doi:10.1029/jb084ib05p02348.
- ^ Woo, Wang-chun (September 2012). "On Earthquake Magnitudes". Hong Kong Observatory. Archived from the original on May 24, 2017. Retrieved December 18, 2013.
- ^ "Richter scale". Glossary. United States Geological Survey. March 31, 2010.
- ^ Di Giacomo, D., Parolai, S., Saul, J., Grosser, H., Bormann, P., Wang, R. & Zschau, J., 2008. "Rapid determination of the energy magnitude Me," in European Seismological Commission 31st General Assembly, Hersonissos.
- ^ Rivera, L. & Kanamori, H., 2008. "Rapid source inversion of W phase for tsunami warning," in European Geophysical Union General Assembly, pp. A-06228, Vienna.
- ^ Vassiliou, Marius; Kanamori, Hiroo (1982). "The Energy Release in Earthquakes". Bull. Seismol. Soc. Am. 72: 371–387.
- ^ Spence, William; Sipkin, Stuart A.; Choy, George L. (1989). "Measuring the Size of an Earthquake". Earthquakes and Volcanoes. 21 (1).
- ^ Lahr, J.C. (1980). HYPOELLIPSE: A computer program for determining local earthquake hypocentral parameters, magnitude, and first-motion pattern. US Geological Survey open-file report (Report). Vol. 80–59.
- ^ al-Arifi, Nassir S.; al-Humidan, Saad (July 2012). "Local and regional earthquake magnitude calibration of Tabuk analog sub-network, Northwest of Saudi Arabia". Journal of King Saud University – Science. 24 (3): 257–263. doi:10.1016/j.jksus.2011.04.001.
- ^ Al-Arifi, Nassir S.; Al-Humidan, Saad (July 2012). "Local and regional earthquake magnitude calibration of Tabuk analog sub-network, Northwest of Saudi Arabia". Journal of King Saud University – Science. 24 (3): 257–263. doi:10.1016/j.jksus.2011.04.001.
Sources
[edit]- Bolt, B. A. (1993), Earthquakes and geological discovery, Scientific American Library, ISBN 0-7167-5040-6.
- Boore, D. M. (September 1989), "The Richter scale: its development and use for determining earthquake source parameter" (PDF), Tectonophysics, 166 (1–3): 1–14, doi:10.1016/0040-1951(89)90200-x
- Chung, D. H.; Bernreuter, D. L. (1980), Regional Relationships Among Earthquake Magnitude Scales., NUREG/CR-1457.
- Gutenberg, B.; Richter, C. F. (February 21, 1936), "Discussion: Magnitude and energy of earthquakes", Science, 83 (2147): 183–185, Bibcode:1936Sci....83..183G, doi:10.1126/science.83.2147.183, PMID 17770563.
- Gutenberg, B.; Richter, C. F. (1956b), "Earthquake magnitude, intensity, energy, and acceleration (Second Paper)", Bulletin of the Seismological Society of America, 46 (2): 105–145.
- Hough, S. E. (2007), Richter's scale: measure of an earthquake, measure of a man, Princeton University Press, ISBN 978-0-691-12807-8.
- Hutton, L. K.; Boore, David M. (December 1987), "The ML scale in Southern California" (PDF), Nature, 271: 411–414, Bibcode:1978Natur.271..411K, doi:10.1038/271411a0.
- Kanamori, Hiroo (February 2, 1978), "Quantification of Earthquakes" (PDF), Nature, 271 (5644): 411–414, Bibcode:1978Natur.271..411K, doi:10.1038/271411a0.
- Richter, C. F. (January 1935), "An Instrumental Earthquake Magnitude Scale" (PDF), Bulletin of the Seismological Society of America, 25 (1): 1–32, archived from the original (PDF) on July 10, 2018, retrieved March 14, 2018.