HOME

TheInfoList



OR:

The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an
earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or strength of an earthquake — an event occurring at greater or lesser depth. (The "" scale is widely used.) The MMI scale measures intensity of shaking, at any particular location, on the surface. It was developed from
Giuseppe Mercalli Giuseppe Mercalli (21 May 1850 – 19 March 1914) was an Italian volcanologist and Catholic priest. He is known best for the Mercalli intensity scale for measuring earthquake intensity. Biography Born in Milan, Mercalli was ordained a Roman ...
's Mercalli intensity scale of 1902. While shaking experienced at the surface is caused by the seismic energy released by an earthquake, earthquakes differ in how much of their energy is radiated as seismic waves. They also differ in the depth at which they occur; deeper earthquakes have less interaction with the surface, their energy is spread throughout a larger volume, and the energy reaching the surface is spread across a larger area. Shaking intensity is localised. It generally diminishes with distance from the earthquake's
epicentre The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a s ...
, but it can be amplified in
sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...
s and in certain kinds of unconsolidated soils. Intensity scales categorise intensity empirically, based on the effects reported by untrained observers, and are adapted for the effects that might be observed in a particular region. By not requiring instrumental measurements, they are useful for estimating the magnitude and location of historical (pre-instrumental) earthquakes: the greatest intensities generally correspond to the epicentral area, and their degree and extent (possibly augmented by knowledge of local geological conditions) can be compared with other local earthquakes to estimate the magnitude.


History

Italian volcanologist
Giuseppe Mercalli Giuseppe Mercalli (21 May 1850 – 19 March 1914) was an Italian volcanologist and Catholic priest. He is known best for the Mercalli intensity scale for measuring earthquake intensity. Biography Born in Milan, Mercalli was ordained a Roman ...
formulated his first intensity scale in 1883. It had six degrees or categories, has been described as "merely an adaptation" of the then-standard
Rossi–Forel scale The Rossi–Forel scale was one of the first seismic scales to represent earthquake intensities. Developed by Michele Stefano Conte de Rossi of Italy and François-Alphonse Forel of Switzerland during the late 19th century, it was used commonly f ...
of 10 degrees, and is now "more or less forgotten". Mercalli's second scale, published in 1902, was also an adaptation of the Rossi–Forel scale, retaining the 10 degrees and expanding the descriptions of each degree. This version "found favour with the users", and was adopted by the Italian Central Office of Meteorology and Geodynamics. In 1904, Adolfo Cancani proposed adding two additional degrees for very strong earthquakes, "catastrophe" and "enormous catastrophe", thus creating a 12-degree scale. His descriptions being deficient,
August Heinrich Sieberg August Heinrich Sieberg (born 23 December 1875 in Aachen; died 18 November 1945 in Jena) was a German geophysicist. He researched mainly in the field of seismology and developed a seismic intensity scales as well as a tsunami intensity scale. Si ...
augmented them during 1912 and 1923, and indicated a
peak ground acceleration Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an wikt:accelerogram, accelerogram at a ...
for each degree. This became known as the "Mercalli–Cancani scale, formulated by Sieberg", or the "Mercalli–Cancani–Sieberg scale", or simply "MCS",. and was used extensively in Europe and remains in use in Italy by the
National Institute of Geophysics and Volcanology The National Institute of Geophysics and Volcanology (, INGV) is a research institute for geophysics Geophysics () is a subject of natural science concerned with the physical processes and Physical property, properties of Earth and its surround ...
(INGV). When Harry O. Wood and Frank Neumann translated this into English in 1931 (along with modification and condensation of the descriptions, and removal of the acceleration criterion), they named it the "modified Mercalli intensity scale of 1931" (MM31). Some seismologists refer to this version as the "Wood–Neumann scale". Wood and Neumann also had an abridged version, with fewer criteria for assessing the degree of intensity. The Wood–Neumann scale was revised in 1956 by
Charles Francis Richter Charles Francis Richter (; April 26, 1900September 30, 1985) was an American seismologist and physicist. He is the namesake and one of the creators of the Richter scale, which, until the development of the moment magnitude scale in 1979, was w ...
and published in his influential textbook ''Elementary Seismology''. Not wanting to have this intensity scale confused with the
Richter scale The Richter scale (), also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale, is a measure of the strength of earthquakes, developed by Charles Richter in collaboration with Beno Gutenberg, and pr ...
he had developed, he proposed calling it the "modified Mercalli scale of 1956" (MM56). In their 1993 compendium of historical seismicity in the United States, Carl Stover and Jerry Coffman ignored Richter's revision, and assigned intensities according to their slightly modified interpretation of Wood and Neumann's 1931 scale, effectively creating a new, but largely undocumented version of the scale. The basis by which the
United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...
(and other agencies) assigns intensities is nominally Wood and Neumann's MM31. However, this is generally interpreted with the modifications summarised by Stover and Coffman because in the decades since 1931, "some criteria are more reliable than others as indicators of the level of ground shaking".. Also, construction codes and methods have evolved, making much of built environment stronger; these make a given intensity of ground shaking seem weaker. Also, some of the original criteria of the most intense degrees (X and above), such as bent rails, ground fissures, landslides, etc., are "related less to the level of ground shaking than to the presence of ground conditions susceptible to spectacular failure". The categories "catastrophe" and "enormous catastrophe" added by Cancani (XI and XII) are used so infrequently that current USGS practice is to merge them into a single category "Extreme" abbreviated as "X+".


Scale values

The lesser degrees of the MMI scale generally describe the manner in which the earthquake is felt by people. The greater numbers of the scale are based on observed structural damage. This table gives MMIs that are typically observed at locations near the epicentre of the earthquake.


Correlation with magnitude

Magnitude and intensity, while related, are very different concepts. Magnitude is a function of the energy liberated by an earthquake, while intensity is the degree of shaking experienced at a point on the surface, and varies from some maximum intensity at or near the epicentre, out to zero at distance. It depends upon many factors, including the depth of the
hypocentre A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its p ...
, terrain, distance from the epicentre, whether the underlying strata there amplify surface shaking, and any directionality due to the earthquake mechanism. For example, a magnitude 7.0 quake in
Salta Salta () is the capital and largest city in the Provinces of Argentina, Argentine province of Salta Province, the same name. With a population of 618,375 according to the 2010 census, it is also the List of cities in Argentina, 7th most-populous ...
, Argentina, in 2011, that was 576.8 km deep, had a maximum felt intensity of V, while a magnitude 2.2 event in
Barrow-in-Furness Barrow-in-Furness is a port town and civil parish (as just "Barrow") in the Westmorland and Furness district of Cumbria, England. Historic counties of England, Historically in the county of Lancashire, it was incorporated as a municipal borou ...
, England, in 1865, about 1 km deep, had a maximum felt intensity of VIII. The small table is a rough guide to the degrees of the MMI scale. The colours and descriptive names shown here differ from those used on certain shake maps in other articles.


Estimating site intensity and its use in seismic hazard assessment

Dozens of intensity-prediction equations have been published to estimate the macroseismic intensity at a location given the magnitude, source-to-site distance, and perhaps other parameters (e.g. local site conditions). These are similar to ground motion-prediction equations for the estimation of instrumental strong-motion parameters such as
peak ground acceleration Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an wikt:accelerogram, accelerogram at a ...
. A summary of intensity prediction equations is available. Such equations can be used to estimate the
seismic hazard A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold. With a hazard thus estimated, risk can be assessed and inc ...
in terms of macroseismic intensity, which has the advantage of being related more closely to
seismic risk Seismic risk or earthquake risk is the potential impact on the built environment and on people's well-being due to future earthquakes. Seismic risk has been defined, for most management purposes, as the potential economic, social and environment ...
than instrumental strong-motion parameters.


Correlation with physical quantities

The MMI scale is not defined in terms of more rigorous, objectively quantifiable measurements such as shake amplitude, shake frequency, peak velocity, or peak acceleration. Human-perceived shaking and building damage 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 many MMI values may be measured for the same earthquake. These values can be displayed best using a contoured map of equal intensity, known as an
isoseismal map In seismology, an isoseismal map is used to show Contour line, countour lines of equally felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters, particularly where no seismometer ...
. However, each earthquake has only one magnitude.


See also

*
European macroseismic scale The European Macroseismic Scale (EMS) is the basis for evaluation of seismic intensity in European countries and is also used in a number of countries outside Europe. Issued in 1998 as an update of the test version from 1992, the scale is referred ...
*
Japan Meteorological Agency seismic intensity scale The Japan Meteorological Agency (JMA) Seismic Intensity Scale (known in Japan as the Shindo seismic scale) is a seismic intensity scale used in Japan to categorize the intensity of local ground shaking caused by earthquakes. The JMA intensit ...
(Shindo scale) * Rohn emergency scale *
Seismic intensity scales Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake. They are distinguished from seismic magnitude scales, which measure the magnitude or overall stren ...
*
Seismic magnitude scales Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at ...
*
Spectral acceleration Spectral acceleration (SA) is a unit measured in ''g'' (the acceleration due to Earth's gravity, equivalent to g-force) that describes the maximum acceleration in an earthquake on an object – specifically a damped, harmonic oscillator moving in ...
*
Strong ground motion In seismology, strong ground motion is the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forci ...


References


Notes


Citations


Sources

* *. *. *. * * * *. *. * * * *. * *


Further reading

* *


External links


National Earthquake Information Center (U.S.)

Modified Mercalli Intensity Scale
United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

The Severity of an Earthquake
nited States Geological Survey
U.S. Earthquake Intensity Database
NOAA The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency charged with forecasting weather, monitoring oceanic and atmospheric conditions, charting the seas, conducting deep-sea exploratio ...

Earthquake IntensityWhat controls the shaking you feel?
IRIS Consortium IRIS (Incorporated Research Institutions for Seismology) was a university research consortium dedicated to exploring the Earth's interior through the collection and distribution of seismographic data. It operated the U.S. National Science Foundati ...
{{Seismic scales Seismic intensity scales Italian inventions