SafekipediaModified Mercalli intensity scale
Adapted from Wikipedia · Adventurer experience
The Modified Mercalli intensity scale (MM, MMI, or MCS) measures how strong an earthquake feels in a specific place. This is different from the seismic magnitude, which tells us about the power of the earthquake itself.
The MMI scale looks at how much the ground shakes in one spot on the surface. It started from a scale made by Giuseppe Mercalli in 1902. Even though an earthquake's shaking comes from energy deep underground, how much shaking people feel can change a lot depending on where they are.
Shaking usually gets weaker the farther you are from the earthquake's epicentre. But it can get stronger in places with soft soil or deep valleys called sedimentary basins. This scale helps us understand old earthquakes, too, because it uses what people felt instead of special tools.
History
Italian scientist Giuseppe Mercalli made a scale in 1883 to measure how earthquakes affect people and buildings. His first scale had six levels. He made a new version in 1902 with ten levels, and it became popular with Italian experts.
In 1904, a scientist named Adolfo Cancani suggested adding two more levels for very strong earthquakes. Another scientist, August Heinrich Sieberg, improved the scale in the 1910s by adding details about how much the ground shook. This version was called the "Mercalli–Cancani–Sieberg scale" and is still used in Italy by the National Institute of Geophysics and Volcanology.
In 1931, Harry O. Wood and Frank Neumann translated the scale into English and made some changes. They called it the "modified Mercalli intensity scale." In 1956, Charles Francis Richter updated it again. Today, scientists at the United States Geological Survey use a version based on the 1931 work, with updates to fit modern buildings and better measuring methods.
Scale values
The Modified Mercalli intensity scale tells us how people feel an earthquake and the damage it causes. Lower numbers show how the earthquake feels, while higher numbers show how much damage happens.
The scale helps us learn more about earthquakes, but it is not the same as measuring how strong the earthquake was. Earthquakes can feel very different depending on where you are, how deep the earthquake is, and what the ground is like.
| Scale level | Peak ground acceleration (approx.) | Ground conditions | Examples |
|---|---|---|---|
| I. Not felt | 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. | |
| 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. | |
| 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. | |
| 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. | |
| 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. | |
| 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. | |
| 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. | ||
| 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. |
| Magnitude | Typical Maximum Modified Mercalli Intensity |
|---|---|
| 1.0–3.0 | I |
| 3.0–3.9 | II–III |
| 4.0–4.9 | IV–V |
| 5.0–5.9 | VI–VII |
| 6.0–6.9 | VII–IX |
| 7.0 and higher | VIII or higher |
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This article is a child-friendly adaptation of the Wikipedia article on Modified Mercalli intensity scale, available under CC BY-SA 4.0.
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