Moment magnitude scale

Updated: 12/30/2025, 12:48:24 PM Wikipedia source

The moment magnitude scale (MMS; denoted explicitly with Mw  or Mwg and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. Mw  was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Similar to the local magnitude/Richter scale (ML ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale. Moment magnitude (Mw ) is considered the authoritative magnitude scale for ranking earthquakes by size. It is more directly related to the energy of an earthquake than other scales, and does not saturate – that is, it does not underestimate magnitudes as other scales do in certain conditions. It has become the standard scale used by seismological authorities like the United States Geological Survey for reporting large earthquakes (typically M > 4), replacing the local magnitude (ML ) and surface-wave magnitude (Ms ) scales. Subtypes of the moment magnitude scale (Mww , etc.) reflect different ways of estimating the seismic moment.

Tables

· Comparative energy released by two earthquakes › Comparison with TNT equivalents

3

3

Mw

3

ES(Joules)

2.0 · 1090

TNT-equivalency(tons)

-

equivalence Hiroshima-bomb(12.5 kT TNT)

-

4

4

Mw

4

ES(Joules)

6.3 · 1010

TNT-equivalency(tons)

00,000,000,015

equivalence Hiroshima-bomb(12.5 kT TNT)

0,000,000.0012

5

5

Mw

5

ES(Joules)

2.0 · 1012

TNT-equivalency(tons)

00,000,000.475

equivalence Hiroshima-bomb(12.5 kT TNT)

0,000,000.0380

6

6

Mw

6

ES(Joules)

6.3 · 1013

TNT-equivalency(tons)

00,000,015,000

equivalence Hiroshima-bomb(12.5 kT TNT)

0,000,001.2000

7

7

Mw

7

ES(Joules)

2.0 · 1015

TNT-equivalency(tons)

00,000,475,000

equivalence Hiroshima-bomb(12.5 kT TNT)

0,000,038.0000

8

8

Mw

8

ES(Joules)

6.3 · 1016

TNT-equivalency(tons)

00,015,000,000

equivalence Hiroshima-bomb(12.5 kT TNT)

0,001,200.0000

9

9

Mw

9

ES(Joules)

2.0 · 1018

TNT-equivalency(tons)

00,475,000,000

equivalence Hiroshima-bomb(12.5 kT TNT)

0,038,000.0000

10

10

Mw

10

ES(Joules)

6.3 · 1019

TNT-equivalency(tons)

15,000,000,000

equivalence Hiroshima-bomb(12.5 kT TNT)

1,200,000.0000

Mw	ES(Joules)	TNT-equivalency(tons)	equivalence Hiroshima-bomb(12.5 kT TNT)
3	2.0 · 1090	-	-
4	6.3 · 1010	00,000,000,015	0,000,000.0012
5	2.0 · 1012	00,000,000.475	0,000,000.0380
6	6.3 · 1013	00,000,015,000	0,000,001.2000
7	2.0 · 1015	00,000,475,000	0,000,038.0000
8	6.3 · 1016	00,015,000,000	0,001,200.0000
9	2.0 · 1018	00,475,000,000	0,038,000.0000
10	6.3 · 1019	15,000,000,000	1,200,000.0000

References

These are normally not bolded. In the technical literature a single bolded "M" – with or without italicization – is used
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Bormann, Wendt & Di Giacomo 2013, p. 18.
The "USGS Earthquake Magnitude Policy" for reporting earthquake magnitudes to the public as formulated by the USGS Earth
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Suzuki 2001, p. 121. See also Figure 2-22 in Richter 1958 (copy in Bormann, Wendt & Di Giacomo 2013, p. 60), which repli
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See Bormann & Saul 2009 for an overview.
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See Seismic magnitude scales.
Kanamori 1977, p. 2981.
ISC-EHB Event 879136 [IRIS]. ISC-EHB Event 869809 [IRIS].
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Pujol 2003b, pp. 165, 167; Miyake 2017, p. 118.
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Aki 1966a, p. 24.
Bormann, Wendt & Di Giacomo 2013, p. 12, equation 3.1.
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Bormann, Wendt & Di Giacomo 2013, p. 14; Bormann & Di Giacomo 2011, p. 412.
Bormann, Wendt & Di Giacomo 2013, pp. 39–40.
Bormann, Wendt & Di Giacomo 2013, p. 7.
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Bormann, Wendt & Di Giacomo 2013, p. 86
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Das, Menesis & Urrutia 2023
Kostrov 1974; Dahlen 1977.
Choy & Boatwright 1995
FAQs – Measuring Earthquakes: How much energy is released in an earthquake? United States Geological Survey
https://web.archive.org/web/20120314043321/https://earthquake.usgs.gov/learn/faq/?faqID=33
"Erdbeben – wenn die Erde zurückschlägt"
https://www.wdr.de/tv/applications/fernsehen/wissen/quarks/pdf/Q_Erdbeben.pdf
"Technical Terms used on Event Pages" n.d.
Tsuboi et al. 1995.
Bormann, Wendt & Di Giacomo 2013, §3.2.8.2, p. 135.
Bormann, Wendt & Di Giacomo 2013, §3.2.8.3, pp. 137–128.
Geophysical Research Letters
https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017GL073801