Mercalli intensity scale
The Modified Mercalli intensity scale (or MMI scale) measures how much a place is shaking because of an earthquake.
The MMI scale is different from scales that measure magnitude like the moment magnitude scale and the Richter scale, because they only measure the amount of energy that the earthquake releases. Different types of soil, the depth of the earthquake, and the distance from the epicenter can all change how much shaking the earthquake produces, even if the earthquake has the same magnitude. but the MMI scale and other intensity scales can help by only measuring how much shaking the earthquake is causing. Since different cities will have different levels of shaking, the MMI scale can also be used to give a different intensity for each city.
Scale values
[change | change source]The lower levels of the Modified Mercalli Intensity scale is based on how the shaking is felt by people. The higher levels of the scale are based on how the shaking damages buildings.
The table here gives Modified Mercalli scale intensities that are usually observed at locations near the epicenter of the earthquake.[1]
| Scale level | Ground conditions |
|---|---|
| I. Not felt | Not felt except for very sensitive people. |
| II. Weak | Only felt by a few people who are not moving, especially on the top of high buildings. Suspended objects may swing a little. |
| III. Weak | Felt well by people inside of buildings, especially on the top of high buildings. Many people do not realize it is an earthquake. Parked cars may move side-to-side a bit. Shaking feels similar to a truck passing by. |
| IV. Light | Felt by many people inside of buildings, but only by a few people outside. At night, some people wake up. Dishes, windows, and doors rattle, and walls make cracking sounds. The feeling is like a heavy truck hitting a building. Parked cars move side-to-side. |
| V. Moderate | Felt by almost everyone, many people wake up at night. Some dishes and windows break. Unstable objects fall over. Pendulum clocks might stop. |
| VI. Strong | Felt by everyone, and many people are scared. Some heavy furniture is moved. Plaster might fall from the walls. There is only slight damage. |
| VII. Very strong | Damage is negligible in buildings that were designed well and built well, but there is slight or moderate damage in regular buildings. Damage is considerable in buildings that were not designed well or not built well. Some chimneys fall over. Felt by people in cars. |
| VIII. Severe | There is slight damage in buildings designed especially for earthquakes. Damage is substantial in regular buildings, with some parts of the buildings collapsing. Damage is great in buildings that were not built well. Chimneys, factory stacks, columns, monuments, and walls fall over. Heavy furniture is overturned. Small amounts of sand and mud come out of the ground. Water in wells changes. People in cars are disturbed. |
| IX. Violent | Damage is considerable in buildings designed especially for earthquakes. Well-designed frame buildings collapse. Damage is great in big buildings, with parts of them collapsing. Buildings are moved off of their foundations. Soil liquefaction happens. Pipes underground are broken. |
| X. Extreme | Some well-built buildings from wood are destroyed. Most masonry and frame buildings are destroyed, even with foundations. Rails bend. Landslides happen a lot next to rivers and hills. Sand and mud in the ground moves. Water spills over the sides of rivers. |
| XI. Extreme | Very few masonry buildings are still standing. Bridges are destroyed. Wide cracks appear in the ground. Pipes underground are completely destroyed. The ground sinks and landslides happen on soft ground. Rails bend greatly. |
| XII. Extreme | Damage is total. Waves are seen on the ground. Everything seems distorted. The shaking throws objects up into the air. |
History
[change | change source] | This article is a translation-work in progress of the article Modified Mercalli Scale from Non-simple English to English. If you are confident enough in your competence of Non-simple English and English, you can help Wikipedia by assisting in the translation. |
When Giuseppe Mercalli (1850-1914) made the original Mercalli intensity scale in 1902, it only had ten levels. In 1904, Adolfo Cancani suggested adding two more levels to the scale to make a twelve-level scale, and August Heinrich Sieberg changed those two levels in 1912 and 1913. For this reason, the scale is sometimes named Mercalli-Cancani-Sieberg scale, or MCS scale.
In 1931, Harry O. Wood and Frank Neumann translated the scale into English, they named it the "modified Mercalli intensity scale of 1931" (MM31), which some seismologists just called it the "Wood–Neumann scale". In 1956, Charles Francis Richter edited the scale and published it in his book Elementary Seismology.[2]
Related pages
[change | change source]References
[change | change source]- ↑ "Magnitude / Intensity Comparison". USGS. Archived from the original on 2019-10-02. Retrieved 2017-08-31.
- ↑ Richter 1958; Musson, Grünthal & Stucchi 2010, p. 416.