Modified Mercalli intensity scale

The Modified Mercalli intensity scale (MM or MMI), descended from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the effects of an earthquake at a given location, distinguished from the earthquake's inherent force or strength as measured by seismic magnitude scales (such as the "Mw" magnitude usually reported for an earthquake). While shaking is driven by the seismic energy released by an earthquake, earthquakes differ in how much of their energy is radiated as seismic waves. Deeper earthquakes also have less interaction with the surface, and their energy is spread out across a larger area. Shaking intensity is localized, generally diminishing with distance from the earthquake's epicenter, but can be amplified in sedimentary basins and certain kinds of unconsolidated soils.

Intensity scales empirically categorize the intensity of shaking based on the effects reported by untrained observers, and are adapted for the effects that might be observed in a particular region.[1] In 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 with knowledge of local geological conditions) can be compared with other local earthquakes to estimate the magnitude.

History

The Italian volcanologist Giuseppe Mercalli formulated his first intensity scale in 1883.[2] It had six degrees or categories, has been described as "merely an adaptation" of the then standard Rossi–Forel scale of ten degrees, and is now "more or less forgotten."[3] Mercalli's second scale, published in 1902, was also an adaptation of the Rossi‒Forel scale, retaining the ten degrees and expanding the descriptions of each degree.[4] This version "found favour with the users", and was adopted by the Italian Central Office of Meteorology and Geodynamics.[5]

In 1904 Adolfo Cancani proposed adding two additional degrees for very strong earthquakes, "catastrophe" and "enormous catastrophe", thus creating the 12 degree scale.[6] His descriptions being deficient, August Heinrich Sieberg augmented them in 1912 and 1923, and indicated a peak ground acceleration (PGA) for each degree.[7] This became known as the "Mercalli–Cancani scale, formulated by Sieberg", or the "Mercalli–Cancani–Sieberg scale", or simply "MCS",[8] and used extensively in Europe.

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 criteria), they called it the "Modified Mercalli Intensity Scale of 1931".[9] (MM31. Some seismologists prefer to call this version the "Wood–Neumann scale".[10]) 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 and published in his influential textbook Elementary Seismology.[11] Not wanting to have this intensity scale confused with the magnitude scale he had developed, he proposed calling it the "Modified Mercalli scale of 1956" (MM56).[12]

In their 1993 compendium of historical seismicity in the United States,[13] 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,[14] effectively creating a new but largely undocumented version of the scale.[15]

The basis by which the U. S. Geological Survey (and other agencies) assigns intensities is nominally Wood and Neumann's "Modified Mercalli Intensity Scale of 1931". However, this is generally interpreted with the modifications summarized by Stover and Coffman because in the decades since 1931 it has been found that "some criteria are more reliable than others as indicators of the level of ground shaking."[16] Also, construction codes and methods have evolved, making much of built environment stronger; these make a given intensity of ground shaking seem weaker.[17] And it is now recognized that some of the original criteria of the higher 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...."[18]

The "catastrophe" and "enormous catastrophe" categories added by Cancani (XI and XII) are used so infrequently that current USGS practice is merge them into a single "Extreme" labeled "X+".[19]

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.

This table gives Modified Mercalli scale intensities that are typically observed at locations near the epicenter of the earthquake.[20]

I. Not felt Not felt except by very few under especially favorable conditions.
II. Weak Felt only by a few people at rest, especially on upper floors of buildings.
III. Weak Felt quite noticeably by people 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. Light 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. Moderate Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
VI. Strong Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
VII. Very strong 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. Severe 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. Violent 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. Liquefaction.
X. Extreme Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
XI. Extreme Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipe lines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII. Extreme Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.

Correlation with magnitude

Magnitude Magnitude / intensity comparison
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 and higher VIII or higher
Magnitude/intensity comparison, USGS

The correlation between magnitude and intensity is far from total, depending upon several factors including the depth of the hypocenter, terrain, distance from the epicenter. For example, on May 19, 2011, an earthquake of magnitude 0.7 in Central California, United States, 4 km deep was classified as of intensity III by the United States Geological Survey (USGS) over 100 miles (160 km) away from the epicenter (and II intensity almost 300 miles (480 km) from the epicenter), while a 4.5 magnitude quake in Salta, Argentina, 164 km deep was of intensity I.[21]

The small table is a rough guide to the degrees of the Modified Mercalli Intensity scale.[20][22] The colors 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 so-called intensity prediction equations[23] 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. A summary of intensity prediction equations is available. Such equations can be used to estimate the seismic hazard in terms of macroseismic intensity, which has the advantage of being more closely related to seismic risk than instrumental strong-motion parameters[24].

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. Human-perceived shaking and building damages are best correlated with peak acceleration for lower-intensity events, and with peak velocity for higher-intensity events.[25]

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 of equal intensity, known as an isoseismal map. However, each earthquake has only one magnitude.

See also

References

  1. ^ "The Modified Mercalli Intensity Scale". USGS.
  2. ^ Davison 1921, p. 103.
  3. ^ Musson, Grünthal & Stucchi 2010, p. 414.
  4. ^ Davison 1921, p. 108.
  5. ^ Musson, Grünthal & Stucchi 2010, p. 415.
  6. ^ Davison 1921, p. 112.
  7. ^ Davison 1921, p. 114.
  8. ^ Musson, Grünthal & Stucchi 2010, p. 416.
  9. ^ Wood & Neumann 1931.
  10. ^ Musson, Grünthal & Stucchi 2010, p. 416.
  11. ^ Richter 1958; Musson, Grünthal & Stucchi 2010, p. 416.
  12. ^ Musson, Grünthal & Stucchi 2010, p. 416.
  13. ^ Stover & Coffman 1993.
  14. ^ Their modifications were mainly to degrees IV and V, with VI contingent on reports of damage to man-made structures, and VII considering only "damage to buildings or other man-made structures". See details at Stover & Coffman 1993, pp. 3–4.
  15. ^ Grünthal 2011, p. 238. The most definitive exposition of the Stover and Coffman's effective scale is at Musson & Cecić 2012, §12.2.2.
  16. ^ Dewey et al. 1995, p. 5.
  17. ^ Davenport & Dowrick 2002.
  18. ^ Dewey et al. 1995, p. 5.
  19. ^ Musson, Grünthal & Stucchi 2010, p. 423.
  20. ^ a b "Magnitude / Intensity Comparison". USGS.
  21. ^ USGS: Did you feel it? for 20 May 2011
  22. ^ "Modified Mercalli Intensity Scale". Association of Bay Area Governments (ABAG).
  23. ^ Allen, Trevor I.; Wald, David J.; Worden, C. Bruce (2012-07-01). "Intensity attenuation for active crustal regions". Journal of Seismology. 16 (3): 409–433. doi:10.1007/s10950-012-9278-7. ISSN 1383-4649.
  24. ^ Musson, R.M.W. (2000). "Intensity-based seismic risk assessment". Soil Dynamics and Earthquake Engineering. 20 (5–8): 353–360. doi:10.1016/s0267-7261(00)00083-x.
  25. ^ "ShakeMap Scientific Background". USGS. Archived from the original on 2009-08-25. Retrieved 2017-09-02.

External links

1590 Neulengbach earthquake

The Neulengbach earthquake of 1590 occurred on 15 September shortly before midnight amidst a long series of much weaker seismic activity starting on 29 June and with aftershocks reported until 12 November. It was the strongest historically documented earthquake in what today is Northeastern Austria.

1732 Irpinia earthquake

The 1732 Irpinia earthquake was a seismic event with a magnitude of 6.6 that affected Irpinia and part of Sannio. It occurred on 29 November 1732 at 8:40 AM local time (UTC+1). The epicenter was located in the Campanian Apennines, in the area of the Ufita Valley, which is part of the modern-day Province of Avellino. Around twenty populated areas were destroyed entirely or in part and tens of others were significantly damaged. The number of deaths was estimated to be 1,940. Damage from the earthquake was classified as "severe" (indicating damage between $5 and $24 million USD), and the number of homes destroyed as classified as "many" (indicating between 101 and 1,000 homes). The earthquake had a rating on the modified Mercalli intensity scale of X (extreme).Among the most devastated communities were Mirabella Eclano (which was razed to the ground), Carife, Grottaminarda, and Ariano Irpino. Damage was serious in the provincial capital of Avellino, while in Benevento, there were mainly partial collapses of buildings.

1929 Grand Banks earthquake

The 1929 Grand Banks earthquake (also called the Laurentian Slope earthquake and the South Shore Disaster) occurred on November 18. The shock had a moment magnitude of 7.2 and a maximum Rossi–Forel intensity of VI (Strong tremor) and was centered in the Atlantic Ocean off the south coast of Newfoundland in the Laurentian Slope Seismic Zone.

1931 in science

The year 1931 in science and technology involved some significant events, listed below.

1964 Alaska earthquake

The 1964 Alaskan earthquake, also known as the Great Alaskan earthquake and Good Friday earthquake, occurred at 5:36 PM AKST on Good Friday, March 27. Across south-central Alaska, ground fissures, collapsing structures, and tsunamis resulting from the earthquake caused about 131 deaths.Lasting four minutes and thirty-eight seconds, the magnitude 9.2 megathrust earthquake remains the most powerful earthquake recorded in North American history, and the second most powerful earthquake recorded in world history. Six hundred miles (970 km) of fault ruptured at once and moved up to 60 ft (18 m), releasing about 500 years of stress buildup. Soil liquefaction, fissures, landslides, and other ground failures caused major structural damage in several communities and much damage to property. Anchorage sustained great destruction or damage to many inadequately earthquake-engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other man-made equipment), particularly in the several landslide zones along Knik Arm. Two hundred miles (320 km) southwest, some areas near Kodiak were permanently raised by 30 feet (9 m). Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet (2.4 m), requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.

In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 32 people between the collapse of the Valdez city harbor and docks, and inside the ship that was docked there at the time. Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there; survivors out-ran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Washington, Oregon, and California. Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was also reported from Florida and Texas.

1971 in science

The year 1971 in science and technology involved some significant events, listed below.

1985 Mexico City earthquake

The 1985 Mexico City earthquake struck in the early morning of 19 September at 07:17:50 (CST) with a moment magnitude of 8.0 and a Mercalli intensity of IX (Violent). The event caused serious damage to the Greater Mexico City area and the deaths of at least 5,000 people. The sequence of events included a foreshock of magnitude 5.2 that occurred the prior May, the main shock on 19 September, and two large aftershocks. The first of these occurred on 20 September with a magnitude of 7.5 and the second occurred seven months later on 30 April 1986 with a magnitude of 7.0. They were located off the coast along the Middle America Trench, more than 350 kilometres (220 mi) away, but the city suffered major damage due to its large magnitude and the ancient lake bed that Mexico City sits on. The event caused between three and four billion USD in damage as 412 buildings collapsed and another 3,124 were seriously damaged in the city.

2005 Qeshm earthquake

The 2005 Qeshm earthquake occurred on November 27 at 13:52 IRST (10:22 UTC) on the sparsely populated Qeshm Island off Southern Iran, killing 13 people and devastating 13 villages. It was Iran's second major earthquake of 2005, following that at Zarand in February. The epicenter was about 1,500 kilometers (930 mi) south of Tehran, close to Iran's southern borders. Initial measurements showed that the earthquake registered about 6.0 on the moment magnitude scale, although that was reduced to 5.8 after further analysis. More than 400 minor aftershocks followed the main quake, 36 of which were greater than magnitude 2.5. The earthquake occurred in a remote area during the middle of the day, limiting the number of fatalities. Iranian relief efforts were effective and largely adequate, leading the country to decline offers of support from other nations and UNICEF.

Qeshm Island is part of the Simply Folded Belt, the most seismically active part of the Zagros fold and thrust belt. Similar to most earthquakes in the area, the 2005 event resulted from reverse slip faulting. Since it lies in such a seismically active area, there is a high risk of destructive earthquakes in Iran; 1 in 3,000 deaths are attributable to earthquakes. One geophysicist has cited the lack of strict building codes as a serious concern.

Earthquake zones of India

The Indian subcontinent has a history of devastating earthquakes. The major reason for the high frequency and intensity of the earthquakes is that the Indian plate is driving into Asia at a rate of approximately 47 mm/year. Geographical statistics of India show that almost 54% of the land is vulnerable to earthquakes. A World Bank and United Nations report shows estimates that around 200 million city dwellers in India will be exposed to storms and earthquakes by 2050. The latest version of seismic zoning map of India given in the earthquake resistant design code of India [IS 1893 (Part 1) 2002] assigns four levels of seismicity for India in terms of zone factors. In other words, the earthquake zoning map of India divides India into 4 seismic zones (Zone 2, 3, 4 and 5) unlike its previous version, which consisted of five or six zones for the country. According to the present zoning map, Zone 5 expects the highest level of seismicity whereas Zone 2 is associated with the lowest level of seismicity.

Giuseppe Mercalli

Giuseppe Mercalli (21 May 1850 – 19 March 1914) was an Italian volcanologist and Catholic priest. He is best remembered for the Mercalli intensity scale for measuring earthquakes.

Harry O. Wood

Harry Oscar Wood (1879 – 1958) was an American seismologist who made several significant contributions in the field of seismology in the early twentieth-century. Following the 1906 earthquake in San Francisco, California, Wood expanded his background of geology and mineralogy and his career took a change of direction into the field of seismology. In the 1920s he co-developed the torsion seismometer, a device tuned to detect short-period seismic waves that are associated with local earthquakes. In 1931 Wood, along with another seismologist, redeveloped and updated the Mercalli Intensity Scale, a seismic scale that is still in use as a primary means of rating an earthquake's effects.

Interplate earthquake

An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other. The slipping process creates an earthquake with relative displacement on either side of the fault, resulting in seismic waves which travel through the Earth and along the Earth's surface. Relative plate motion can be lateral as along a transform fault boundary, vertical if along a convergent boundary (i.e. subduction or thrust/reverse faulting) or a divergent boundary (i.e. rift zone or normal faulting), and oblique, with horizontal and lateral components at the boundary. Interplate earthquakes associated at a subduction boundary are called megathrust earthquakes, which are the most powerful earthquakes.

Intraplate earthquakes are often confused with interplate earthquakes, but are fundamentally different in origin, occurring within a single plate rather than between two tectonic plates on a plate boundary. The specifics of the mechanics by which they occur, as well as the intensity of the stress drop which occurs after the earthquake also differentiate the two types of events. Intraplate earthquakes have, on average, a higher stress drop than that of an interplate earthquake and generally higher intensity.

Lake Voulismeni

Lake Voulismeni (Greek: Λίμνη Βουλισμένη, Límni Voulisméni) is a former sweetwater small lake, later connected to the sea, located at the centre of the town of Agios Nikolaos on the Greek island of Crete. It has a circular shape of a diameter of 137 m and depth 48.8m. The locals refer to it as simply "the lake". The lake is connected to the harbour of the town by a channel dug in 1907. A panoramic view of the lake can be seen from a small park situated above it.

According to legend, the goddess Athena bathed in it. Every year at midnight turning to Orthodox Christian Easter day, the majority of the population of the town gathers around the lake to celebrate with fireworks, and firecrackers thrown by the people attending that highlight event.The rocks at the lake are limestone breccias, the result of undersea landslides coming down from the mountains to the north-west of the town.

A normal fault which cuts right through the town in a roughly NNE to SSW direction passes directly through the north-western side of the lake, the cliff at the lake is the scarp slope of this fault. Elsewhere in the town the fault was later buried by subsequent underwater landslides. An underground stream that was cut by this fault created a solution sinkhole and a small cave following the disappearance of the overlying sea during the Messinian Salinity Crisis. After only a few hundred thousand years the small cave, dissolved out of the unstable and structurally weak breccia, collapsed creating a deep hole. The destabilised breccia at the top of this hole subsided into the hole creating a deep funnel-shaped sinkhole which was subsequently filled with freshwater by the still running spring. The creation of the Mediterranean Sea during the Zanclean Flood left a deep, spring-fed, freshwater lake that overflowed via a small stream into the nearby sea.

In 1852 Captain Thomas Spratt surveyed eastern Crete on behalf of the Royal Navy and recorded the lake as being '...a small circular pool of brackish water' and '....having a small stream opening out of it into the sea', clear evidence that the spring was still flowing at that time. He also measured the depth of the lake as 210 feet (64m) and it is this figure that is used in almost all publications and writings about the lake today. In September 2000 the geology department of the University of Athens conducted a detailed underwater survey of the lake, they found its maximum depth to be only 48.8m. The results of this survey appear not to have been widely publicised outside the geological community.

On 12th October 1856 a massive earthquake occurred in the sea off Crete with an epicentre only 40km from the lake. Although its magnitude was not recorded it was listed as grade XI on the Modified Mercalli Intensity Scale, one grade down from the maximum possible. This earthquake was most likely responsible for the blocking or diversion of the freshwater spring leading to the later stagnation of the lake and the collapse of the western corner of the lake which reduced the lake depth from the 64m measured by Thomas Spratt to the 48.8m today.

By the end of the 19th Century the lake was stagnant, it was known locally as Vromolimni, 'the stinky lake'. The digging of the channel to the sea in order that the more dense seawater could flush away the stagnant water and the smell most likely happened in 1907 when the French Army were stationed in the town as guarantors of Cretan independence prior to union with Greece.

List of earthquakes in 2019

This is a list of earthquakes in 2019. Only earthquakes of magnitude 6 or above are included, unless they result in damage and/or casualties, or are notable for other reasons. All dates are listed according to UTC time. Maximum intensities are indicated on the Modified Mercalli intensity scale and are sourced from United States Geological Survey (USGS) ShakeMap data.

MMIS

MMIS may refer to:

Maintenance Management Information System

Medicaid Management Information System

Manara Management Information System

Modified Mercalli intensity scale

Rohn emergency scale

The Rohn emergency scale is a scale on which the magnitude (intensity) 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 ratified in two later independent publications. It is the first scale that quantifies any emergency based on a mathematical model. The scale can be tailored for use at any geographic level – city, county, state or continent. It can be used to monitor the development of an ongoing emergency event, as well as forecast the probability and nature of a potential developing emergency and in the planning and execution of a National Response Plan.

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, forcing the use of accelerographs (or strong ground motion accelerometers) for recording. The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, and rupture velocity.

As seismic instruments (and accelerometers in particular) become more common, it becomes necessary to correlate expected damage with instrument-readings. The old Modified Mercalli intensity scale (MM), a relic of the pre-instrument days, remains useful in the sense that each intensity-level provides an observable difference in seismic damage.

After many years of trying every possible manipulation of accelerometer-time histories, it turns out that the extremely simple peak ground velocity (PGV) provides the best correlation with damage. PGV merely expresses the peak of the first integration of the acceleration record. Accepted formulae now link PGV with MM Intensity. Note that the effect of soft soils gets built into the process, since one can expect that these foundation conditions will amplify the PGV significantly.

"ShakeMaps" are produced by the United States Geological Survey, provide almost-real-time information about significant earthquake events, and can assist disaster-relief teams and other agencies.

Modern scales
Historical scales

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