Mercalli intensity scale

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The Mercalli Intensity Scale is one of many scales used to classify the intensity of an earthquake by examining its effects on people and structures at the Earth's surface. Two such scales were devised by Italian volcanologist Giuseppe Mercalli in 1883 and 1902, the second of which was widely used before the Richter scale. The 1902 version of the scale had ten degrees, and this was expanded by Cancani in 1904 to twelve degrees. The whole scale was completely re-written by Sieberg, and Sieberg's version was modified and published in English by Wood and Neumann in 1931 as the Modified Mercalli Scale. The phrase Mercalli Intensity should not be used unless one really means the original ten degree scale of 1902.

The lower numbers of the 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 table that follows is a rough guide to the degrees of the Modified Mercalli (MM) scale.

I. Instrumental	Not felt except by a very few under especially favorable conditions.
II. Feeble	Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
III. Slight	Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated.
IV. Moderate	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. Dishes and windows rattle.
V. Rather Strong	Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects overturned. Clocks may stop.
VI. Strong	Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.
VII. Very Strong	Difficult to stand; furniture broken; damage negligible in building 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. Noticed by persons driving motor cars.
VIII. Destructive	Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved.
IX. Ruinous	General panic; 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. Disastrous	Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent.
XI. Very Disastrous	Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly.
XII. Catastrophic	Total damage - Almost 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 may move.

Information from The Severity of an earthquake pamphlet of the United States Geological Survey, the website of the U.S. National Earthquake Information Center in Golden, Colorado, http://www.seismo.unr.edu/ftp/pub/louie/class/100/mercalli.html and http://www.geography-site.co.uk/pages/physical/earth/richt.htmlbg:Скала на Меркали-Канкани-Зиберг de:Mercalliskala es:Escala de Mercalli fr:Échelle de Mercalli id:Skala Mercalli it:Scala Mercalli ms:Skala Mercalli nl:Schaal van Mercalli ja:メルカリ震度階級 no:Mercalliskalaen nn:Mercalliskalaen pl:Skala Mercallego pt:Escala de Mercalli ro:Scara Mercalli sv:Mercalliskalan vi:Thang đo Mercalli zh:麥加利地震烈度