Mercalli intensity scale

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The Mercalli intensity scale (or more precisely the Modified Mercalli intensity scale) is a scale to measure the intensity of earthquakes. Unlike with the Richter scale, the Mercalli scale does not take into account energy of an earthquake directly. Rather, they classify earthquakes by the effects they have (and the destruction they cause). When there is little damage, the scale describes how people felt the earthquake, or how many people felt it.

Very often, non-geologists use this scale, because it is easier for people to describe what damage an earthquake caused, than to do calculations to get a value on the Richter scale.

Values range from I - Instrumental to XII - Catastrophic.

Giuseppe Mercalli (1850-1914) originally developed the scale, with ten levels. In 1902, Adolfo Cancani extended the scale to include twelve levels. August Heinrich Sieberg completely rewrote the scale. For this reason, the scale is sometimes named Mercalli-Cancani-Sieberg scale, or MCS scale.

Harry O. Wood and Frank Neumann translated it into English, and published it as Mercalli–Wood–Neumann (MWN) scale. Charles Francis Richter also edited it. He also developed the Richter scale, later on.

Modified Mercalli Intensity scale[change | change source]

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 damage to structures

The large table gives Modified Mercalli scale intensities that are typically observed at locations near the epicenter of the earthquake.[1]

This is an accurate representation

The Scale under here is also a really good source for the Mercalli Scale.

    1. No feeling at all
No signs of feeling anywhere                            
    1. 2. A little bit of feeling
Only some people can feel it. Mainly of top floors of buildings
    1. 3. A tiny bit stronger than weak
It is noticed more by people inside buildings, usually noticed by people on top floors of buildings. Not really realized as an Earthquake.
1.4.Light Shock It is felt more often by people indoors and outside. You can feel it at night. Cars are rocked noticeably.
    1. 5. Moderate feeling
Felt by nearly everyone. Dishes broken. Pendulum clocks might stop working. Unstable objects can be unturned
    1. 6. Strong quake
It is felt by all people. Many have been frightened by it. Slight damage done. Heavy objects are sometimes moved.
    1. 7. Very strong feeling
A lot of damage to poorly built houses. Some chimneys broken in houses. Slight damage to other buildings.
VII. Very Strong
    1. 8. Severe quake
Slight damage to great structured buildings. Most heavy objects are overturned. Walls, chimneys collapsed in.
    1. 9. Violent
Great sustainable buildings are damaged. Buildings fall of foundations. Well designed structures thrown down.
1.10. Dangerous Many buildings collapse and underground pipes are torn apart. Water is thrown out rivers
    1. 11. Extremely Dangerous
Few structures are still standing. Bridges are destroyed. Pipes under ground are out of service. The Earth slumps.
    1. 12. Catastrophic
Waves can be seen on the ground. Damage is total. Objects are thrown up in the air. Lines of sight and level distorted.
I. Not felt Not felt by humans but technology is capable of sensing it.
II. Very Weak Felt only by a few persons indoors, especially on upper floors of buildings. Duration estimated by some indoors trying to sleep.
III. Weak Felt quite noticeably by persons indoors, especially on upper floors of buildings. Felt by nearly everyone indoors trying to sleep. Might be felt by very few outdoors at rest. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
IV. Light Felt indoors by many, outdoors by few during the day. At night, some awakened. Felt by everyone indoors trying to sleep. Frightened no one or very few. Noticed by people walking. Dishes, windows, doors disturbed. Walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
V. Moderate Felt by nearly everyone; many awakened. Few frightened. Some dishes, windows broken. Some light furniture moved. Unstable objects overturned. Pendulum clocks may stop. Pictures and books crooked. A few instances of cracked plaster. Slight unsteadiness in walking. Sensation like heavy train passing next to the building. Direction estimated.
VI. Strong Felt by all, many frightened. All or virtually all awakened. Some heavy furniture moved. Pictures and books fall. A few instances of fallen plaster. A few drivers stop, especially if at slow speeds or on smooth roads. People walk unsteadily. Sensation like a powerful bomb being detonated next to the building. Damage slight. A few people injured.
VII. Very Strong Frightened all. Everyone runs outdoors. People run unsteadily. Many drivers stop. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
VIII. Severe Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Drivers' steering is affected. A few people killed.
IX. Violent Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Poorly built or badly designed structures may succumb to total collapse. Buildings shifted off foundations.
X. Extreme Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
XI. Extremely Dangerous Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipe lines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII. Catastrophic Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air. Few, if any, survivors.

Correlation with magnitude[change | change source]

Magnitude Typical Maximum
Modified Mercalli Intensity
Under 2.0 I
2.0 – 2.9 IIIII
3.0 – 3.9 IIIIV
4.0 – 4.9 IVV
5.0 – 5.9 VVI
6.0 – 6.9 VIVII
7.0 – 7.9 VIIVIII
8.0 or higher VIII or higher

There is a correlation between the magitude and the intensity of the earthquake. Even though this correlation is there, it may be difficult to link one to the other: This correlation depends on several factors, such as 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.[2]

The small table is a rough guide to the degrees of the Modified Mercalli Intensity scale.[1][3] The colors and descriptive names shown here differ from those used on certain shake maps in other articles. However, it will not be 100% accurate.

Related pages[change | change source]

References[change | change source]

  1. 1.0 1.1 "Magnitude / Intensity Comparison". USGS. Archived from the original on 2019-10-02. Retrieved 2017-08-31.
  2. USGS: Did you feel it? for 20 May 2011
  3. "Modified Mercalli Intensity Scale". Association of Bay Area Governments (ABAG).