Mercalli scale

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Earthquakes are measured by their intensity and magnitude. An earthquake's intensity readings are based on observed effects, for example, ground shaking and damage. An earthquake's intensity differs in separate locations, depending on the distance of the location from the earthquake's epicenter. The ranking system used to measure seismic intensity is called the Mercalli Scale. Michele Stefano de Rossi and FranÇois to Alphonse Forel formulated the Mercalli Scale in 1878. Harry O. Wood and Frank Neumann modified it in 1931.

An earthquake's magnitude reading is based on the amount of seismic energy released at the hypocenter of the earthquake. It is based on the magnitude of the earthquake waves. The ranking system used to measure earthquake magnitudes is called the Richter scale.

Last updated: June 16, 2004.

n.
A scale of earthquake intensity based on observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction).

[After Giuseppi Mercalli (1850-1914), Italian seismologist.]

[Etymology: G. Mercalli; Italy 1850-1914] geophysics A qualitative scale for the intensity of an earthquake based on observed effects (hence its values are local, and various for any one earthquake), ranging from 1 upwards, often written using Roman numerals. Created as a 10-level scale in 1902
[Mercalli G. Boll. Soc. Sismologica Italiana Vol. 8, 184-91 (1902)] from the widely used Rossi Forel scale of 1883, the Mercalli scale was expanded to 12 levels and progressively adjusted to give the MM Scale or modified Mercalli Scale of 1931.
[Wood H. O., Neumann F. Bull. Seis. Soc. Amer. Vol. 21, 277-83 (1931)] A single number quoted for a particular earthquake represents the maximum, but, because of different distances from the epicentre and the further complication of the depth below the epicentre of the true centre, this number does not characterize the earthquake as a geophysical event, but as a geographic if not purely socio-economic event. (The Richter scale, in contrast, is computed singly for any one earthquake, and represents the geophysical dimension.) The following brief interpretation of the MM Scale is based on that of Richter.
[Richter C. F. Elementary Seismology (San Francisco: W. H. Freeman, 1958)]

I	Registered by seismographs, but felt by very few people and those only in especially sensitive conditions.
II	Felt by a few people at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
III	Felt noticeably by many people indoors, especially on upper floors of buildings, but not necessarily recognized as an earthquake, vibration being similar to that of any passing truck. Standing vehicles may rock. Has discernible duration.
IV	Dishes, windows, doors and hung items disturbed; walls make cracking sound. Some sleepers wakened. Sensation as from heavy truck striking building. Outdoors felt by some, standing vehicles rock noticeably.
V	Felt generally indoors and out. Doors and lighter loose objects displaced.
VI	Felt by all, frightening for most, causing them to seek the outdoors. Fragile items break and many items fall from shelves and walls. Furniture displaced. Some cracking of weak masonry.
VII	Some cracking of ordinary masonry and plasterboard; displacement of exposed and weaker masonry, falling bricks, etc. Waves on water bodies, earth-slides on unstable slopes, people falling over.
VIII	Some disturbing of goods including reinforced masonry, with general collapsing of chimneys, towers, monuments. Frame houses shifted. Trees broken, moving cars displaced. More slipping and cracking of the ground.
IX	Widespread collapsing of all but specially resistant masonry, conspicuous cracking of ground with damage to reservoirs and pipelines. General panic.
X	General destruction of all but specially resistant buildings, bridges, etc. Major landslides and horizontal shifting of sand, mud and water bodies; serious damage to associated earthworks. Some bending of steel rails.
XI	General destruction of buildings and widespread damage to underground works. Major damage to steel rails.
XII	Extensive displacement of ground, virtually complete destruction of structures.

A measurement of the intensity of an earthquake.

Modified Mercalli scale of earthquake intensity
I Felt by very few, except under special circumstances.
II Felt by a few persons at rest, especially on the upper floors of buildings.
III Felt noticeably indoors, although not always recognized as an earthquake. Vibration like passing lorry.
IV Felt by many indoors during daytime, but by few outdoors. Some awakened at night. Vibration like lorry striking building.
V Felt by nearly everyone; many awakened. Some breakages, disturbances of trees, telegraph poles.
VI Felt by all; many run outside. Some heavy furniture moved.
VII Everyone runs outside. No damage in well-built buildings; moderate damage in ordinary structures; considerable damage in poorly constructed buildings.
VIII Considerable damage except in specially constructed buildings. Disturbs people driving cars.
IX Damage even in specially designed structures. Buildings shifted from foundations; ground cracked; underground pipes broken.
X Ground badly cracked. Railway lines bent. Landslides considerable.
XI Few brick-built structures remain standing, if any. Bridges destroyed. Broad fissures in the ground.
XII Total damage. Waves observed on ground surface. Objects thrown upward into the air.

Adapted from US Geological Survey.