Understanding the MMI scale (Modified Mercalli Intensity scale)

The Mercalli intensity scale is a scale used for measuring the intensity of an earthquake. The scale quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures on a scale from I (not felt) to XII (total destruction).

I MMI (Instrumental)
Not felt except by a very few under especially favorable conditions.






II MMI (Weak shaking)
Felt only by a few persons at rest, especially on upper floors of buildings.





III MMI (Weak shaking)
Felt quite noticeably by persons indoors, especially on upper floors of buildings. 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 MMI (Light shaking)
Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.





V MMI (Moderate shaking)
Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.





VI MMI (Strong shaking)
Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.





VII MMI (Very strong shaking)
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 MMI (Violent shaking)
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.




IX MMI (Violent shaking)
Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.





X MMI (Extreme shaking)
Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.






Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.





Damage total. Lines of sight and level are distorted. Objects thrown into the air.




Text : courtesy USGS (United States)
Great graphics : courtesy BMKG (Indonesia)
Introduction : courtesy Wikipedia