Modified Mercalli Intensity Scale
The lower degrees of the Modified Mercalli Intensity scale generally deal with the manner in which the earthquake is felt by people. The higher numbers of the scale are based on observed structural damage.
The small table is a rough guide to the degrees of the Modified Mercalli Intensity scale. The colors and descriptive names shown here differ from those used on certain shake maps in other articles.
The large table gives Modified Mercalli scale intensities that are typically observed at locations near the epicenter of the earthquake.
The correlation between magnitude and intensity is far from total, depending upon several factors including the depth of the earthquake, terrain, population density, and damage. For example, on May 19, 2011 an earthquake of magnitude 0.7 in Central California, United States 4 km deep was classified as of intensity III by the United States Geological Survey (USGS) over 100 miles (160 km) away from the epicenter (and II intensity almost 300 miles (480 km) from the epicenter), while a 4.5 magnitude quake in Salta, Argentina 164 km deep was of intensity I.
| Magnitude | Typical Maximum Modified Mercalli Intensity |
|---|---|
| Under 2.0 | I |
| 2.0 – 2.9 | I – II |
| 3.0 – 3.9 | II – IV |
| 4.0 – 4.9 | IV – VI |
| 5.0 – 5.9 | V – VIII |
| 6.0 – 6.9 | VII – X |
| 7.0 – 9.9 | VIII or higher; up to XII |
| 10.0 or higher | X or higher; up to XII |
| I. Instrumental | Generally not felt by people unless in favorable conditions. |
|---|---|
| II. Weak | Felt only by a few people at rest, especially on the upper floors of buildings. Delicately suspended objects (including chandeliers) may swing slightly. |
| III. Slight | Felt quite noticeably by people indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing automobiles may rock slightly. Vibration similar to the passing of a truck. Duration can be estimated. Indoor objects (including chandeliers) may shake. |
| IV. Moderate | Felt indoors by many to all people, and outdoors by few people. Some awakened. Dishes, windows, and doors disturbed, and walls make cracking sounds. Chandeliers and indoor objects shake noticeably. The sensation is more like a heavy truck striking building. Standing automobiles rock noticeably. Dishes and windows rattle alarmingly. Damage none. |
| V. Rather Strong | Felt inside by most or all, and outside. Dishes and windows may break and bells will ring. Vibrations are more like a large train passing close to a house. Possible slight damage to buildings. Liquids may spill out of glasses or open containers. None to a few people are frightened and run outdoors. |
| VI. Strong | Felt by everyone, outside or inside; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books fall off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight to moderate to poorly designed buildings, all others receive none to slight damage. |
| VII. Very Strong | Difficult to stand. Furniture broken. Damage light in building of good design and construction; slight to moderate in ordinarily built structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by people driving automobiles. |
| VIII. Destructive | Damage slight in structures of good design, considerable in normal buildings with a possible partial collapse. Damage great in poorly built structures. Brick buildings easily receive moderate to extremely heavy damage. Possible fall of chimneys, factory stacks, columns, monuments, walls, etc. Heavy furniture moved. |
| IX. Violent | General panic. Damage slight to moderate (possibly heavy) in well-designed structures. Well-designed structures thrown out of plumb. Damage moderate to great in substantial buildings, with a possible partial collapse. Some buildings may be shifted off foundations. Walls can fall down or collapse. |
| X. Intense | Many well-built structures destroyed, collapsed, or moderately to severely damaged. Most other structures destroyed, possibly shifted off foundation. Large landslides. |
| XI. Extreme | Few, if any structures remain standing. Numerous landslides, cracks and deformation of the ground. |
| XII. Catastrophic | Total destruction – everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The ground moves in waves or ripples. Large amounts of rock move position. Landscape altered, or leveled by several meters. Even the routes of rivers can be changed. |
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