Mercalli intensity scale
The Mercalli intensity scale is a seismic scale
Seismic scale
A seismic scale is used to calculate and compare the severity of earthquakes....

 used for measuring the intensity of an earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

. It measures the effects of an earthquake, and is distinct from the moment magnitude  usually reported for an earthquake (sometimes described as the obsolete Richter magnitude), which is a measure of the energy released. The intensity of an earthquake is not totally determined by its magnitude.

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). Values depend upon the distance to the earthquake, with the highest intensities being around the epicentral
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...

 area. Data gathered from people who have experienced the quake are used to determine an intensity value for their location. The Mercalli (Intensity) scale originated with the widely-used simple ten-degree Rossi-Forel scale
Rossi-Forel scale
The Rossi–Forel scale was one of the first seismic scales to reflect earthquake intensities. Developed by Michele Stefano Conte de Rossi of Italy and François-Alphonse Forel of Switzerland in the late 19th century, it was used for about two decades until the introduction of the Mercalli intensity...

, which was revised by Italian vulcanologist Giuseppe Mercalli
Giuseppe Mercalli
Giuseppe Mercalli was an Italian volcanologist. He is best remembered today for his Mercalli scale for measuring earthquakes which is still used today.-Biography:...

 in 1884 and 1906.

In 1902 the ten-degree Mercalli scale was expanded to twelve degrees by Italian physicist Adolfo Cancani. It was later completely re-written by the German geophysicist August Heinrich Sieberg and became known as the Mercalli-Cancani-Sieberg (MCS) scale.

The Mercalli-Cancani-Sieberg scale was later modified and published in English by Harry O. Wood and Frank Neumann in 1931 as the Mercalli-Wood-Neumann (MWN) scale. It was later improved by Charles Richter, the father of the Richter magnitude scale
Richter magnitude scale
The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....

. The scale is known today as the Modified Mercalli scale or Modified Mercalli Intensity scale, and abbreviated MM or MMI.

Modified Mercalli Intensity scale

The lower degrees of the Modified Mercalli 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 small table is a rough guide to the degrees of the Modified Mercalli Intensity scale. The colors and descriptive names shown here differ from those used on certain shake maps in other articles.

The large table gives Modified Mercalli scale intensities that are typically observed at locations near the epicenter of the earthquake.

The correlation between magnitude and intensity is far from total, depending upon several factors including depth of the earthquake, terrain, and population density. For example, on 19 May 2011 an earthquake of magnitude 0.7 in Southern California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, USA 4 km deep was classified as of intensity III by the United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

 (USGS), while a 4.5 magnitude quake in Salta
Salta is a city in northwestern Argentina and the capital city of the Salta Province. Along with its metropolitan area, it has a population of 464,678 inhabitants as of the , making it Argentina's eighth largest city.-Overview:...

, Argentina 164 km deep was of intensity I.
Moment Magnitude Typical Maximum
Modified Mercalli Intensity
1.0 – 3.0 I
3.0 – 3.9 IIIII
4.0 – 4.9 IVV
5.0 – 5.9 VIVII
6.0 – 6.9 VIIIX
7.0+ VIII or higher

I. Instrumental Generally not felt by people unless in favorable conditions.
II. Weak Felt only by a few people at best, especially on the upper floors of buildings. Delicately suspended objects may swing.
III. Slight Felt quite noticeably by people 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 people, outdoors by few people during the day. At night, some awaken. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rock noticeably. Dishes and windows rattle alarmingly.
V. Rather Strong Felt outside by most, may not be felt by some outside in non-favorable conditions. Dishes and windows may break and large bells will ring. Vibrations like large train passing close to house.
VI. Strong Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books fall 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 people 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. Violent 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. Intense Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent.
XI. Extreme Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly.
XII. Cataclysmic Total destruction – 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 move position. Landscape altered, or leveled by several meters. In some cases, even the routes of rivers are changed.

Correlation with physical quantities

The Mercalli scale is not defined in terms of more rigorous, objectively quantifiable measurements such as shake amplitude, shake frequency, peak velocity, or peak acceleration
Peak ground acceleration
Peak ground acceleration is a measure of earthquake acceleration on the ground and an important input parameter for earthquake engineering, also known as the design basis earthquake ground motion...

. Human perceived shakings and building damages are best correlated with peak acceleration for lower-intensity events, and with peak velocity for higher-intensity events.

Comparison to the moment magnitude scale

The effects of any one earthquake can vary greatly from place to place, so there may be many Mercalli intensity values measured for the same earthquake. These values can be best displayed using a contoured map. Each earthquake, on the other hand, has only one magnitude.

Historical analysis

Earthquake Death Toll Moment Magnitude Mercalli intensity
Tangshan earthquake (1976)
1976 Tangshan earthquake
The Tangshan Earthquake also known as the Great Tangshan Earthquake, was a natural disaster that occurred on July 28, 1976. It is believed to be the largest earthquake of the 20th century by death toll. The epicenter of the earthquake was near Tangshan in Hebei, People's Republic of China, an...

250,000 7.8–8.2 XI
Loma Prieta earthquake (1989)  63 6.9 IX
Kobe earthquake (1995)
Great Hanshin earthquake
The Great Hanshin earthquake, or Kobe earthquake, was an earthquake that occurred on Tuesday, January 17, 1995, at 05:46 JST in the southern part of Hyōgo Prefecture, Japan. It measured 6.8 on the moment magnitude scale , and Mj7.3 on JMA magnitude scale. The tremors lasted for approximately 20...

6,434 6.8 X-XI
Haiti earthquake (2010)
2010 Haiti earthquake
The 2010 Haiti earthquake was a catastrophic magnitude 7.0 Mw earthquake, with an epicentre near the town of Léogâne, approximately west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time on Tuesday, 12 January 2010.By 24 January, at least 52 aftershocks...

316,000 7.0 X
Van earthquake (2011)
2011 Van earthquake
The Van earthquake was a destructive magnitude 7.1 Mw earthquake that struck eastern Turkey near the city of Van on Sunday, 23 October 2011 at 13.41 local time. It occurred at a shallow depth of 20 km , causing heavy shaking across much of eastern Turkey and lighter tremors across neighboring parts...

432+ 7.2 X
Christchurch earthquake (February 2011)  181 6.3 IX
Tōhoku earthquake (2011)
2011 Tōhoku earthquake and tsunami
The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east...

18,500. Totals include tsunami. 9.0 IX

See also

  • Other seismic scales
    Seismic scale
    A seismic scale is used to calculate and compare the severity of earthquakes....

  • Hayward Fault Zone
    Hayward Fault Zone
    The Hayward Fault Zone is a geologic fault zone capable of generating significantly destructive earthquakes. This strike-slip fault is about long, situated mainly along the western base of the hills on the east side of San Francisco Bay...

     for seismic shake maps using the Modified Mercalli scale
  • Japan Meteorological Agency seismic intensity scale
    Japan Meteorological Agency seismic intensity scale
    The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan and Taiwan to measure the intensity of earthquakes. It is measured in units of...

  • Isoseismal map
    Isoseismal map
    In seismology an isoseismal map is used to show lines of equal felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters, particularly where no instrumental records exist, such as for historical earthquakes...

  • Strong ground motion
    Strong ground motion
    "Peak ground velocity" redirects here.Seismologists usually define strong ground motion as the strong earthquake shaking that occurs close to a causative fault...

  • Rohn Emergency Scale
    Rohn Emergency Scale
    The Rohn Emergency Scale is a scale on which the magnitude of an emergency is measured. It was first proposed in 2006, and explained in more detail in a peer-reviewed paper presented at a 2007 system sciences conference. The idea was further refined later that year. The need for such a scale was...

    for measuring the magnitude (intensity) of any emergency

External links

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