Editing Modified Mercalli intensity scale (section)

==Scale values==
The lesser degrees of the MMI scale generally describe the manner in which the earthquake is felt by people. The greater numbers of the scale are based on observed structural damage.

This table gives MMIs that are typically observed at locations near the epicenter of the earthquake.<ref name="comparison">{{cite web|title=Magnitude vs Intensity|url=https://prd-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/atoms/files/Mag_vs_Int_Pkg_1.pdf|url-status=live|archive-url=https://web.archive.org/web/20220305084449/https://prd-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/atoms/files/Mag_vs_Int_Pkg_1.pdf|archive-date=2022-03-05|access-date=2022-03-05|publisher=United States Geological Survey}}</ref>

{| class="wikitable"
! Scale level
! [[Peak ground acceleration]] (approx.)<ref>{{cite web |title=3.5. Representing Macroseismic Intensity on Maps – ShakeMap Documentation documentation |url=https://usgs.github.io/shakemap/manual4_0/ug_intensity.html |website=usgs.github.io |access-date=11 April 2024}}</ref>
! Ground conditions
! Examples
|-
! style="{{shindo/color|mmi|1}}width:180px;text-align:left" id="mmi-1" | <span><big><big>I. Not felt</big></big></span>
| <{{cvt|0.0005|g0|m/s2}}
| Not felt except by very few under especially favorable conditions.
|-
! style="{{shindo/color|mmi|2}}text-align:left" id="mmi-2" | <span><big><big>II. Weak</big></big></span>
| rowspan="2" | {{cvt|0.003|g0|m/s2}}
| Felt only by a few people at rest, especially on upper floors of buildings. Delicately suspended objects may swing. 
|-
! style="{{shindo/color|mmi|3}}text-align:left" id="mmi-3" | <span><big><big>III. Weak</big></big></span>
| Felt quite noticeably by people indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing vehicles may slightly rock. Vibrations are similar to the passing of a truck, with duration estimated.
| [[1992 Nicaragua earthquake]]
|-
! style="{{shindo/color|mmi|4}}text-align:left" id="mmi-4" | <span><big><big>IV. Light</big></big></span>
| {{cvt|0.028|g0|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 and tsunami|2006 Pangandaran earthquake]]
|-
! style="{{shindo/color|mmi|5}}text-align:left" id="mmi-5" | <span><big><big>V. Moderate</big></big></span>
| {{cvt|0.062|g0|m/s2}}
| Felt by nearly everyone; many awakened. Some dishes and windows are broken. Unstable objects are overturned. [[Pendulum clock]]s may stop.
| [[2010 Mentawai earthquake and tsunami|2010 Mentawai earthquake]]<br>[[2025 Drake Passage earthquake]]
|-
! style="{{shindo/color|mmi|6}}text-align:left" id="mmi-6" | <span><big><big>VI. Strong</big></big></span>
| {{cvt|0.12|g0|m/s2}}
| Felt by all, and many are frightened. Some heavy furniture is moved; a few instances of fallen [[Plaster veneer|plaster]] occur. Damage is slight.
| <!--- Please limit to three most recent notable events with 100+ fatalities --->[[2021 West Sulawesi earthquake]]<br>[[2000 Enggano earthquake]]
|-
! style="{{shindo/color|mmi|7}}text-align:left" id="mmi-7" | <span><big><big>VII. Very strong</big></big></span>
| {{cvt|0.22|g0|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.
| <!--- Please limit to three most recent notable events with 1,000+ fatalities --->[[May 1998 Afghanistan earthquake]]<br>[[2002 Hindu Kush earthquakes]]<br>[[2009 Sumatra earthquakes]]
|-
! style="{{shindo/color|mmi|8}}text-align:left" id="mmi-8" | <span><big><big>VIII. Severe</big></big></span>
| {{cvt|0.40|g0|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. 
| <!--- Please limit to three most recent notable events with 1,000+ fatalities --->[[2005 Nias–Simeulue earthquake]]
|-
! style="{{shindo/color|mmi|9}}text-align:left" id="mmi-9" | <span style="color:white;"><big><big>IX. Violent</big></big></span>
| {{cvt|0.75|g0|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. [[Soil liquefaction|Liquefaction]] occurs. Underground pipes are broken. 
| <!--- Please limit to three most recent notable events with 1,000+ fatalities --->[[1977 Vrancea earthquake]] <br>[[2010 Yushu earthquake]]<br>[[2023 Al Haouz earthquake]]
|-
! style="{{shindo/color|mmi|10}}text-align:left" id="mmi-10" | <span style="color: white;"><big><big>X. Extreme</big></big></span>
| rowspan=3 | >{{cvt|1.39|g0|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. 
| <!--- Please limit to three most recent notable events with 1,000+ fatalities ---><br>[[April 2015 Nepal earthquake]]<br>[[2018 Sulawesi earthquake and tsunami|2018 Sulawesi earthquake]]<br>[[2025 Myanmar earthquake]]
|-
! style="{{shindo/color|mmi|11}}text-align:left" id="mmi-11" | <span style="color: white;"><big><big>XI. Extreme</big></big></span>
| 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.
|<!--- Please limit to three most recent notable events with 1,000+ fatalities --->[[2005 Kashmir earthquake]]<br>[[2008 Sichuan earthquake]]<br>[[2024 Noto earthquake]]
|-
! style="{{shindo/color|mmi|12}}text-align:left" id="mmi-12" | <span style="color: white;"><big><big>XII. Extreme</big></big></span>
| Damage is total. Waves are seen on ground surfaces. Lines of sight and level are distorted. Objects are thrown upward into the air. 
|<!--- Please limit to three most recent notable events with 1,000+ fatalities --->[[1939 Erzincan earthquake]]<br>[[1960 Valdivia earthquake]]<br>[[2023 Turkey–Syria earthquakes]] 
|}

=== Correlation with magnitude ===
{| cellspacing="3" cellpadding="3" style="width:20%; border:1px aqua ; background:#eee; margin:0 auto 0 auto; float:right;"
|-
! style="text-align:left" |Magnitude
| '''Typical Maximum Modified Mercalli Intensity'''
|-
! style="text-align:left" |1.0–3.0
| '''I'''
|-
! style="text-align:left" |3.0–3.9
| '''II–III'''
|-
! style="text-align:left" |4.0–4.9
| '''IV–V'''
|-
! style="text-align:left" |5.0–5.9
| '''VI–VII'''
|-
! style="text-align:left" |6.0–6.9
| '''VII–IX'''
|-
! style="text-align:left" |7.0 and higher
| '''VIII or higher'''
|-	
| colspan="2" style="text-align: center;" | <small><span class="plainlinks">[https://web.archive.org/web/20110623113247/http://earthquake.usgs.gov/learn/topics/mag_vs_int.php Magnitude/intensity comparison, USGS]</span></small>
|}

Magnitude and intensity, while related, are very different concepts.  Magnitude is a function of the energy liberated by an earthquake, while intensity is the degree of shaking experienced at a point on the surface, and varies from some maximum intensity at or near the epicenter, out to zero at distance.  It depends upon many factors, including the depth of the [[hypocenter]], terrain, distance from the epicenter, whether the underlying strata there amplify surface shaking, and any directionality due to the earthquake mechanism. For example, a magnitude 7.0 quake in [[Salta]], Argentina, in 2011, that was 576.8&nbsp;km deep, had a maximum felt intensity of V,<ref>{{Cite web |publisher=United States Geological Survey |title=M 7.0 – 26&nbsp;km NNE of El Hoyo, Argentina – Impact |url=https://earthquake.usgs.gov/earthquakes/eventpage/usp000hsdc/impact |website=ANSS Comprehensive Earthquake Catalog}}</ref> while a magnitude 2.2 event in [[Barrow in Furness]], England, in 1865, about 1&nbsp;km deep, had a maximum felt intensity of VIII.<ref name="BGS_online_EQ_database">{{Cite web |url=http://www.quakes.bgs.ac.uk/historical/query_eq/ |title=UK Historical Earthquake Database |publisher=British Geological Survey |access-date=2018-03-15}}</ref>

The small table is a rough guide to the degrees of the MMI scale.<ref name="comparison" /><ref name="abag">{{cite web|title=Modified Mercalli Intensity Scale|url=http://resilience.abag.ca.gov/shaking/mmi/|publisher=[[Association of Bay Area Governments]]|access-date=2017-09-02|archive-date=2023-03-26|archive-url=https://web.archive.org/web/20230326023832/http://resilience.abag.ca.gov/shaking/mmi/|url-status=dead}}</ref> The colors and descriptive names shown here differ from those used on certain shake maps in other articles.

=== Estimating site intensity and its use in seismic hazard assessment ===
Dozens of intensity-prediction equations{{sfn|Allen|Wald|Worden|2012}} have been published to estimate the macroseismic intensity at a location given the magnitude, source-to-site distance, and perhaps other parameters (e.g. local site conditions). These are similar to [[Engineering Seismology|ground motion-prediction equations]] for the estimation of instrumental strong-motion parameters such as [[peak ground acceleration]]. A summary of intensity prediction equations is available.<ref>{{cite web| url = http://www.gmpe.org.uk| title = Ground motion prediction equations (1964–2021) by John Douglas, University of Strathclyde, Glasgow, United Kingdom}}</ref> Such equations can be used to estimate the [[seismic hazard]] in terms of macroseismic intensity, which has the advantage of being related more closely to [[seismic risk]] than instrumental strong-motion parameters.{{sfn|Musson|2000}}

=== Correlation with physical quantities ===
The MMI scale is not defined in terms of more rigorous, objectively quantifiable measurements such as shake amplitude, shake frequency, peak velocity, or peak acceleration. Human-perceived shaking and building damage are best correlated with peak acceleration for lower-intensity events, and with peak velocity for higher-intensity events.<ref>{{cite web|title=ShakeMap Scientific Background|url=https://earthquake.usgs.gov/eqcenter/shakemap/background.php|publisher=United States Geological Survey|access-date=2017-09-02|archive-url=https://web.archive.org/web/20090825092714/http://earthquake.usgs.gov/eqcenter/shakemap/background.php|archive-date=2009-08-25|url-status=dead}}</ref>

=== Comparison to the moment magnitude scale ===
The effects of any one earthquake can vary greatly from place to place, so many MMI values may be measured for the same earthquake. These values can be displayed best using a contoured map of equal intensity, known as an [[isoseismal map]]. However, each earthquake has only one magnitude.