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Modified Mercalli intensity scale

Updated: 12/11/2025, 5:50:21 PM Wikipedia source

The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or strength of an earthquake — an event occurring at greater or lesser depth. (The "Mw" scale is widely used.) The MMI scale measures intensity of shaking, at any particular location, on the surface. It was developed from Giuseppe Mercalli's Mercalli intensity scale of 1902. While shaking experienced at the surface is caused by the seismic energy released by an earthquake, earthquakes differ in how much of their energy is radiated as seismic waves. They also differ in the depth at which they occur; deeper earthquakes have less interaction with the surface, their energy is spread throughout a larger volume, and the energy reaching the surface is spread across a larger area. Shaking intensity is localised. It generally diminishes with distance from the earthquake's epicentre, but it can be amplified in sedimentary basins and in certain kinds of unconsolidated soils. Intensity scales categorise intensity empirically, based on the effects reported by untrained observers, and are adapted for the effects that might be observed in a particular region. By not requiring instrumental measurements, they are useful for estimating the magnitude and location of historical (pre-instrumental) earthquakes: the greatest intensities generally correspond to the epicentral area, and their degree and extent (possibly augmented by knowledge of local geological conditions) can be compared with other local earthquakes to estimate the magnitude.

Tables

· Scale values
I. Not felt
I. Not felt
Scale level
I. Not felt
Peak ground acceleration (approx.)
<0.0005 g0 (0.0049 m/s2)
Ground conditions
Not felt except by very few under especially favorable conditions.
Examples
2007–2008 Nazko earthquakes
II. Weak
II. Weak
Scale level
II. Weak
Peak ground acceleration (approx.)
0.003 g0 (0.029 m/s2)
Ground conditions
Felt only by a few people at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
Examples
2012 El Salvador earthquake
III. Weak
III. Weak
Scale level
III. Weak
Peak ground acceleration (approx.)
Felt quite noticeably by people indoors, especially on upper floors of buildings. Many people do not recognise it as an earthquake. Standing vehicles may slightly rock. Vibrations are similar to the passing of a truck, with duration estimated.
Ground conditions
1992 Nicaragua earthquake
IV. Light
IV. Light
Scale level
IV. Light
Peak ground acceleration (approx.)
0.028 g0 (0.27 m/s2)
Ground conditions
Felt indoors by many, outdoors by few during the day. At night, some are awakened. Dishes, windows, and doors are disturbed; walls make cracking sounds. Sensations are like a heavy truck striking a building. Standing vehicles are rocked noticeably.
Examples
2006 Pangandaran earthquake
V. Moderate
V. Moderate
Scale level
V. Moderate
Peak ground acceleration (approx.)
0.062 g0 (0.61 m/s2)
Ground conditions
Felt by nearly everyone; many awakened. Some dishes and windows are broken. Unstable objects are overturned. Pendulum clocks may stop.
Examples
mw- .mw- 1947 Wisconsin earthquake 2010 Mentawai earthquake 2021 East Java earthquake
VI. Strong
VI. Strong
Scale level
VI. Strong
Peak ground acceleration (approx.)
0.12 g0 (1.2 m/s2)
Ground conditions
Felt by all, and many are frightened. Some heavy furniture is moved; a few instances of fallen plaster occur. Damage is slight.
Examples
2000 Enggano earthquake 2015 Sabah earthquake 2021 West Sulawesi earthquake
VII. Very strong
VII. Very strong
Scale level
VII. Very strong
Peak ground acceleration (approx.)
0.22 g0 (2.2 m/s2)
Ground conditions
Damage is negligible in buildings of good design and construction; but slight to moderate in well-built ordinary structures; damage is considerable in poorly built or badly designed structures; some chimneys are broken. Noticed by motorists.
Examples
2002 Hindu Kush earthquakes 2009 Sumatra earthquakes 2016 southern Taiwan earthquake
VIII. Severe
VIII. Severe
Scale level
VIII. Severe
Peak ground acceleration (approx.)
0.40 g0 (3.9 m/s2)
Ground conditions
Damage is slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage is great in poorly built structures. The fall of chimneys, factory stacks, columns, monuments, and walls occur. Heavy furniture is overturned. Sand and mud is ejected in small amounts. Changes occur in well water. Motorists are disturbed.
Examples
May 1998 Afghanistan earthquake 2005 Nias–Simeulue earthquake 2023 Herat earthquakes
IX. Violent
IX. Violent
Scale level
IX. Violent
Peak ground acceleration (approx.)
0.75 g0 (7.4 m/s2)
Ground conditions
Damage is considerable in specially designed structures; well-designed frame structures are thrown off-kilter. Damage is great in substantial buildings, with partial collapse. Buildings are shifted off foundations. Liquefaction occurs. Underground pipes are broken.
Examples
2004 Indian Ocean earthquake 2025 Cebu earthquake 2025 Kamchatka earthquake 2025 Kunar earthquake
X. Extreme
X. Extreme
Scale level
X. Extreme
Peak ground acceleration (approx.)
>1.39 g0 (13.6 m/s2)
Ground conditions
Some well-built wooden structures are destroyed; most masonry and frame structures are destroyed with foundations. Rails are bent. Landslides are considerable from river banks and steep slopes. Sand and mud is shifted. Water is splashed over banks.
Examples
April 2015 Nepal earthquake 2018 Sulawesi earthquake 2025 Myanmar earthquake
XI. Extreme
XI. Extreme
Scale level
XI. Extreme
Peak ground acceleration (approx.)
Few, if any, (masonry) structures remain standing. Bridges are destroyed. Broad fissures erupt in the ground. Underground pipelines are rendered completely out of service. Earth slumps and landslips occur on soft ground. Rails are greatly bent.
Ground conditions
2005 Kashmir earthquake 2008 Sichuan earthquake 2024 Noto earthquake
XII. Extreme
XII. Extreme
Scale level
XII. Extreme
Peak ground acceleration (approx.)
Damage is total. Waves are seen on ground surfaces. Lines of sight and level are distorted. Objects are thrown upward into the air.
Ground conditions
1950 Assam-Tibet earthquake 1960 Valdivia earthquake 2023 Turkey–Syria earthquakes
Scale level
Peak ground acceleration (approx.)
Ground conditions
Examples
I. Not felt
<0.0005 g0 (0.0049 m/s2)
Not felt except by very few under especially favorable conditions.
2007–2008 Nazko earthquakes
II. Weak
0.003 g0 (0.029 m/s2)
Felt only by a few people at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
2012 El Salvador earthquake
III. Weak
Felt quite noticeably by people indoors, especially on upper floors of buildings. Many people do not recognise it as an earthquake. Standing vehicles may slightly rock. Vibrations are similar to the passing of a truck, with duration estimated.
1992 Nicaragua earthquake
IV. Light
0.028 g0 (0.27 m/s2)
Felt indoors by many, outdoors by few during the day. At night, some are awakened. Dishes, windows, and doors are disturbed; walls make cracking sounds. Sensations are like a heavy truck striking a building. Standing vehicles are rocked noticeably.
2006 Pangandaran earthquake
V. Moderate
0.062 g0 (0.61 m/s2)
Felt by nearly everyone; many awakened. Some dishes and windows are broken. Unstable objects are overturned. Pendulum clocks may stop.
mw- 1947 Wisconsin earthquake 2010 Mentawai earthquake 2021 East Java earthquake
VI. Strong
0.12 g0 (1.2 m/s2)
Felt by all, and many are frightened. Some heavy furniture is moved; a few instances of fallen plaster occur. Damage is slight.
2000 Enggano earthquake 2015 Sabah earthquake 2021 West Sulawesi earthquake
VII. Very strong
0.22 g0 (2.2 m/s2)
Damage is negligible in buildings of good design and construction; but slight to moderate in well-built ordinary structures; damage is considerable in poorly built or badly designed structures; some chimneys are broken. Noticed by motorists.
2002 Hindu Kush earthquakes 2009 Sumatra earthquakes 2016 southern Taiwan earthquake
VIII. Severe
0.40 g0 (3.9 m/s2)
Damage is slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage is great in poorly built structures. The fall of chimneys, factory stacks, columns, monuments, and walls occur. Heavy furniture is overturned. Sand and mud is ejected in small amounts. Changes occur in well water. Motorists are disturbed.
May 1998 Afghanistan earthquake 2005 Nias–Simeulue earthquake 2023 Herat earthquakes
IX. Violent
0.75 g0 (7.4 m/s2)
Damage is considerable in specially designed structures; well-designed frame structures are thrown off-kilter. Damage is great in substantial buildings, with partial collapse. Buildings are shifted off foundations. Liquefaction occurs. Underground pipes are broken.
2004 Indian Ocean earthquake 2025 Cebu earthquake 2025 Kamchatka earthquake 2025 Kunar earthquake
X. Extreme
>1.39 g0 (13.6 m/s2)
Some well-built wooden structures are destroyed; most masonry and frame structures are destroyed with foundations. Rails are bent. Landslides are considerable from river banks and steep slopes. Sand and mud is shifted. Water is splashed over banks.
April 2015 Nepal earthquake 2018 Sulawesi earthquake 2025 Myanmar earthquake
XI. Extreme
Few, if any, (masonry) structures remain standing. Bridges are destroyed. Broad fissures erupt in the ground. Underground pipelines are rendered completely out of service. Earth slumps and landslips occur on soft ground. Rails are greatly bent.
2005 Kashmir earthquake 2008 Sichuan earthquake 2024 Noto earthquake
XII. Extreme
Damage is total. Waves are seen on ground surfaces. Lines of sight and level are distorted. Objects are thrown upward into the air.
1950 Assam-Tibet earthquake 1960 Valdivia earthquake 2023 Turkey–Syria earthquakes

References

  1. Their modifications were mainly to degrees IV and V, with VI contingent on reports of damage to man-made structures, and
  2. "The Severity of an Earthquake"
    https://pubs.usgs.gov/gip/earthq4/severitygip.html
  3. Davison 1921, p. 103.
  4. Musson, Grünthal & Stucchi 2010, p. 414.
  5. Davison 1921, p. 108.
  6. Musson, Grünthal & Stucchi 2010, p. 415.
  7. Davison 1921, p. 112.
  8. Davison 1921, p. 114.
  9. Musson, Grünthal & Stucchi 2010, p. 416.
  10. "Intensity evaluation method"
    https://web.archive.org/web/20221020112435/http://legacy.ingv.it/roma/SITOINGLESE/activities/pererischio/macrosismica/macros/metod_val.html
  11. Wood & Neumann 1931.
  12. Richter 1958; Musson, Grünthal & Stucchi 2010, p. 416.
  13. Stover & Coffman 1993
  14. Grünthal 2011, p. 238. The most definitive exposition of the Stover and Coffman's effective scale is at Musson & Cecić
  15. Dewey et al. 1995, p. 5.
  16. Davenport & Dowrick 2002.
  17. Musson, Grünthal & Stucchi 2010, p. 423.
  18. "Magnitude vs Intensity"
    https://prd-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/atoms/files/Mag_vs_Int_Pkg_1.pdf
  19. U.S. Geological Survey
    https://ghsc.code-pages.usgs.gov/esi/shakemap/manual4_0/ug_intensity.html
  20. ANSS Comprehensive Earthquake Catalog
    https://earthquake.usgs.gov/earthquakes/eventpage/usp0006dzc/impact
  21. "UK Historical Earthquake Database"
    http://www.quakes.bgs.ac.uk/historical/query_eq/
  22. earthquake.usgs.gov
    https://earthquake.usgs.gov/education/calculator.php
  23. "Modified Mercalli Intensity Scale"
    https://web.archive.org/web/20230326023832/http://resilience.abag.ca.gov/shaking/mmi/
  24. Allen, Wald & Worden 2012.
  25. "Ground motion prediction equations (1964–2021) by John Douglas, University of Strathclyde, Glasgow, United Kingdom"
    http://www.gmpe.org.uk
  26. Musson 2000.
  27. "ShakeMap Scientific Background"
    https://web.archive.org/web/20090825092714/http://earthquake.usgs.gov/eqcenter/shakemap/background.php
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