earthquake

1 shaking and vibration at the surface of the earth resulting from underground movement along a fault plane of from volcanic activity [syn: quake, temblor, seism]

2 a disturbance that is extremely disruptive; "selling the company caused an earthquake among the employees"

English

Pronunciation

• IPA: /ˈɜː(r)θˌkweɪk/
• SAMPA: /"3:(r)T%kweIk/

Noun

1. A shaking of the Earth, caused by volcanic activity or movement around geologic faults.
2. A natural disaster.

Synonyms

• quake

Translations

• Bosnian: zemljotres
• Breton: kren-douar
• Catalan: terratrèmol
• Chinese: 地震 (dì-zhèn)
• Croatian: potres
• Czech: zemětřesení
• Danish: jordskælv
• Dutch: aardbeving, aardschok
• Esperanto: tertremo
• Estonian: maavärin
• Finnish: maanjäristys
• French: tremblement de terre , séisme
• German: Erdbeben
• Greek: σεισμός [siˈzmo̞s] , Εγκέλαδος [e̞ˈ(ŋ)ɟe̞laˌðo̞s]
• Italian: terremoto, sisma
• Indonesian: Gempa bumi
• Japanese: 地震 (じしん, jishin)
• Kurdish:
• Latvian: zemestrīce
• Lithuanian: žemės drebėjimas
• Maltese: terremot
• Norwegian: jordskjelv
• Polish: trzęsienie ziemi
• Portuguese: terramoto
• Russian: землетрясение (z'eml'etr'as'énije)
• Romanian: cutremur
• Scottish Gaelic: crith-thalmhainn
• Serbian:

  Cyrillic: земљотрес

  Latin: zemljotres

• Spanish: terremoto , temblor , chaka
• Swahili: tetemeko (noun 5/6)
• Telugu: భూకంపం (bhookampam)
• Tok Pisin: guria
• Turkish: deprem, zelzele

Related terms

• moonquake
• seaquake

See also

• aftershock
• fault line
• Richter scale
• seismic
• seismograph
• seismologist
• seismology
• tremor
• tsunami

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.

At the Earth's surface, earthquakes manifest themselves by a shaking and sometimes displacement of the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity.

In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, huge amounts of gas migration, mainly methane deep within the earth, but also by volcanic activity, landslides, mine blasts, and nuclear experiments.

An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter means the point at ground level directly above this.

Naturally occurring earthquakes

Tectonic earthquakes will occur anywhere within the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. In the case of transform or convergent type plate boundaries, which form the largest fault surfaces on earth, they will move past each other smoothly and aseismically only if there are no irregularities or asperities along the boundary that increase the frictional resistance. Most boundaries do have such asperities and this leads to a form of stick-slip behaviour. Once the boundary has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the Elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.

Earthquakes away from plate boundaries

Where plate boundaries occur within continental lithosphere, deformation is spread out a over a much larger area than the plate boundary itself. In the case of the San Andreas fault continental transform, many earthquakes occur away from the plate boundary and are related to strains developed within the broader zone of deformation caused by major irregularities in the fault trace (e.g. the “Big bend” region). The Northridge earthquake was associated with movement on a blind thrust within such a zone. Another example is the strongly oblique convergent plate boundary between the Arabian and Eurasian plates where it runs through the northwestern part of the Zagros mountains. The deformation associated with this plate boundary is partitioned into nearly pure thrust sense movements perpendicular to the boundary over a wide zone to the southwest and nearly pure strike-slip motion along the Main Recent Fault close to the actual plate boundary itself. This is demonstrated by earthquake focal mechanisms.

All tectonic plates have internal stress fields caused by their interactions with neighbouring plates and sedimentary loading or unloading (e.g. deglaciation). These stresses may be sufficient to cause failure along existing fault planes, giving rise to intra-plate earthquakes.

Deep focus earthquakes

The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, Deep focus earthquakes may occur at much greater depths (up to seven hundred kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. These are earthquakes that occur at a depth at which the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.

Earthquakes and volcanic activity

Earthquakes also often occur in volcanic regions and are caused there, both by tectonic faults and by the movement of magma in volcanoes. Such earthquakes can serve as an early warning of volcanic eruptions.

Earthquake storms

Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in the 20th century, the half dozen large earthquakes in New Madrid in 1811-1812, and has been inferred for older anomalous clusters of large earthquakes in the Middle East and in the Mojave Desert.

Size and frequency of occurrence

Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in Chile, Peru, Indonesia, Iran, Pakistan the Azores in Portugal, Turkey, New Zealand, Greece, Italy, and Japan, Larger earthquakes occur less frequently, the relationship being exponential; for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a particular time period than earthquakes larger than magnitude 5. In the (low seismicity) United Kingdom, for example, it has been calculated that the average recurrences are:

• an earthquake of 3.7 - 4.6 every year
• an earthquake of 4.7 - 5.5 every 10 years
• an earthquake of 5.6 or larger every 100 years.

The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past because of the vast improvement in instrumentation (not because the number of earthquakes has increased). The USGS estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0-7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable. In fact, in recent years, the number of major earthquakes per year has actually decreased, although this is likely a statistical fluctuation. More detailed statistics on the size and frequency of earthquakes is available from the USGS.

Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate. Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.

With the rapid growth of mega-cities such as Mexico City, Tokyo or Tehran, in areas of high seismic risk, some seismologists are warning that a single quake may claim the lives of up to 3 million people.

Effects/impacts of earthquakes

There are many effects of earthquakes including, but not limited to the following:

Shaking and ground rupture

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings or other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation. The ground-shaking is measured by ground acceleration.

Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

Ground rupture is a visible breaking and displacement of the earth's surface along the trace of the fault, which may be of the order of few metres in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations and requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.

Landslides and avalanches

Earthquakes can cause landslides and avalanches, which may cause damage in hilly and mountainous areas.

Fires

Following an earthquake, fires can be generated by break of the electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started.

Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated granular material temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, as buildings or bridges, to tilt or sink into the liquefied deposits.

Tsunami

Undersea earthquakes and earthquake-triggered landslides into the sea, can cause Tsunami. See, for example, the 2004 Indian Ocean earthquake.

Floods

Floods may be a secondary effects of earthquakes, if dams are damaged.

Earthquakes may cause landslips to dam rivers, which then collapse and cause floods.

Human impacts

Earthquakes may result in disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse of buildings or destabilization of the base of buildings which may lead to collapse in future earthquakes.

The most significant human impact is loss of life

Preparation for earthquakes

• Earthquake preparedness
• Household seismic safety
• HurriQuake nail (for resisting hurricanes and earthquakes)
• Seismic retrofit
• Seismic hazard
• Mitigation of seismic motion
• Earthquake prediction

Specific fault articles

• Alpine Fault
• Calaveras Fault
• Cascadia subduction zone
• Geology of the Death Valley area
• Great Sumatran fault
• Hayward Fault Zone
• Hope Fault
• Liquiñe-Ofqui Fault
• North Anatolian Fault Zone
• New Madrid Fault Zone
• San Andreas Fault
• Wasatch Fault

Major earthquakes

Pre-20th century

• Pompeii (62 AD).
• Aleppo Earthquake (1138).
• Basel earthquake (1356). Major earthquake that struck Central Europe in 1356.
• Carniola earthquake (1511). A major earthquake that shook a large portion of South-Central Europe. Its epicenter was around the town of Idrija, in today's Slovenia. It caused great damage to structures all over Carniola, including Ljubljana, and in western Carinthia, particularly in Villach and Klagenfurt which were almost completely destroyed. There was some minor damage in Venice and other cities, too.
• Shaanxi Earthquake (1556). Deadliest known earthquake in history, estimated to have killed 830,000 in China.
• Dover Straits (1580).
• Dubrovnik earthquake (1667). Disastrous earthquake in Dubrovnik, Croatia killed about 3/5 of the population.
• Port Royal Earthquake (1692). An earthquake on June 7, 1692, largely destroyed Port Royal, a safe harbor for pirates, causing two thirds of the city to sink into the Caribbean Sea.
• The great Sicilian earthquake (1693). As many as 100,000 may have died.
• Cascadia Earthquake (1700).
• Tokyo earthquake (1703). 37,000 died.
• Kamchatka earthquakes (1737) The third biggest earthquake on record measuring 9.3 on the Richter scale.
• Lisbon earthquake (1755), one of the most destructive and deadly earthquakes in history, killing between 60,000 and 100,000 people and causing a major tsunami that affected parts of Europe, North Africa and the Caribbean.
• Calabria earthquake (1783). Series of 6 earthquakes in Calabria, Italy killed 50,000.
• Quito earthquake. (1797) Quito, Viceroyalty of Peru, now the capital of Ecuador, was devastated by an earthquake. 40,000 died.
• New Madrid Earthquake (1811), and another tremor (1812) that also struck the small Missouri town, was reportedly the strongest ever in North America and made the Mississippi River temporarily change its direction and permanently altered its course in the region.
• Fort Tejon Earthquake (1857). Estimated Richter Scale above 8, said the strongest earthquake in Southern California history.
• Great Neapolitan Earthquake (1857). Estimated Richter Scale of 6.9. 11,000 dead.
• 1872 Lone Pine earthquake (1872). Might been strongest ever measured in California with an estimated Richter Scale of 8.1 said seismologists.
• Charleston earthquake (1886). Largest earthquake in the southeastern United States, killed 100.
• Ljubljana earthquake (14. IV. 1895), a series of powerful quakes that ultimately had a vital impact on the city of Ljubljana, being a catalyst of its urban renewal.
• Assam earthquake of 1897 (1897). Large earthquake that destroyed all masonry structures, measuring more than 8 on the Richter scale.

20th century

• San Francisco Earthquake (1906). Between 7.7 and 8.3 magnitudes; killed approximately 3,000 people and caused around $400 million in damage; most devastating earthquake in California and U.S. history.
• Messina Earthquake (1908). Killed about 60,000 people.
• Gansu earthquake (1920). Killed 200,000 in Gansu province, China.
• Great Kantō earthquake (1923). On the Japanese island of Honshū, killing over 140,000 in Tokyo and environs.
• 1931 Hawke's Bay earthquake. Occurred in the Hawkes Bay in the North Island of New Zealand leaving 256 dead.
• 1933 Long Beach earthquake
• 1935 Balochistan earthquake at Quetta, Pakistan measuring 7.7 on the Richter scale. Anywhere from 30,000 to 60,000 people died
• 1939 Erzincan earthquake at Erzincan, Turkey measuring 7.9 on the Richter scale.
• Ashgabat earthquake (1948). Earthquake in Ashgabat, Soviet Union measuring 7.3 on the Richter scale killed over 110,000 (2/3 the population of the city).
• Assam earthquake of 1950 (1950). Earthquake in Assam, India measures 8.6M.
• Kamchatka earthquakes (1952 and 1737), measuring >9.0.
• Great Kern County earthquake (1952). This was second strongest tremor in Southern California history, epicentered 60 miles North of Los Angeles. Major damage in Bakersfield, California and Kern County, California, while it shook the Los Angeles area.
• 1959 Yellowstone earthquake, formed Quake Lake in southern Montana, USA
• Great Chilean Earthquake (1960). Strongest earthquake ever recorded, 9.5 on Moment magnitude scale, and generated tsunamis throughout the Pacific ocean. It measured 9.6 on the Richter scale.
• 1960 Agadir earthquake, Morocco with around 15,000 casualties.
• 1963 Skopje earthquake, measuring 6.1 on the Richter scale kills 1,800 people, leaves another 120,000 homeless, and destroys 80% of the city.
• Good Friday Earthquake (1964) In Alaska, it was the fourth biggest earthquake recorded,
• Luzon Earthquake (1990). On 16 July 1990, an earthquake measuring 7.7 on the Richter scale struck the island of Luzon, Philippines.
• Landers, California earthquake (1992). Serious damage in the small town of Yucca Valley, California and was felt across 10 states in Western U.S. Another tremor measured 6.4 struck 3 hours later and felt across Southern California.
• August 1993 Guam Earthquake, measuring 8.2 on the Richter scale and lasting 60 seconds.
• 1993 Latur earthquake Latur Earthquake,an earthquake of magnitude 6.3 on Richter Scale rocked the districts of Latur and Osmanabad in Maharashtra in India.The degree of fury was such that dwellings in several villages of these 2 districts were totally converted to debris. In adjoining Karnataka state, 9 people were killed and about 16,000 people injured. A huge number of houses were damaged.
• Northridge, California earthquake (1994). Damage showed seismic resistance deficiencies in modern low-rise apartment construction.
• Sakhalin earthquake (1995). Measuring 7.6 on the Richter scale, killing over 2,000 people in Sakhalin, Russia.
• Great Hanshin earthquake (1995). Killed over 6,400 people in and around Kobe, Japan.
• 1998 Afghanistan earthquake (1998). 6.9 on the Richter scale. Some 125 villages were damaged and 4000 people killed.
• Athens earthquake (1999). 5.9 on the Richter scale, it hit Athens on September 7. Epicentered 10 miles north of the Greek capital, it claimed 143 lives.
• Chi-Chi earthquake (1999) Also called the 921 earthquake. Struck Taiwan on September 21, 1999. Over 2,000 people killed, destroyed or damaged over ten thousand buildings. Caused world computer prices to rise sharply.
• Armenia, Colombia (1999) 6.2 on the Richter scale, Killed over 2,000 in the Colombian Coffee Grown Zone.
• 1999 İzmit earthquake measuring 7.5 on the Richter scale and killed over 40,000 people and left approximately half a million people homeless in northwestern Turkey.
• Hector Mine earthquake (1999). 7.1 on the Richter scale, epicentered 30 miles east of Barstow, California, widely felt in California and Nevada.
• 1999 Düzce earthquake at Düzce, Turkey measuring 7.2 on the Richter scale.
• Baku earthquake (2000).

21st century

• Nisqually Earthquake (2001).
• El Salvador earthquakes (2001). 7.9 (13 January) and 6.6 (13 February) magnitudes, killed more than 1,100 people.
• Gujarat Earthquake (26 January 2001).
• Hindu Kush earthquakes (2002). Over 1,100 killed.
• Molise earthquake (2002) 26 killed.
• Bam Earthquake (2003). Over 40,000 people are reported dead.
• Parkfield, California earthquake (2004). Not large (6.0), but the most anticipated and intensely instrumented earthquake ever recorded and likely to offer insights into predicting future earthquakes elsewhere on similar slip-strike fault structures.
• Chūetsu earthquake (2004).
• Sumatra-Andaman Earthquake (26 December 2004). By some estimates, the second largest earthquake in recorded history (estimates of magnitude vary between 9.1
• September 2007 Sumatra earthquakes 8.0 magnitude September 12 (2007)
• November 14, 2007, 7.7 magnitude, Antofagasta, Chile (2007).
• November 29, 2007, 7.4 magnitude, Caribbean Sea (2007).
• December 20, 2007 6.8 magnitude, Gisborne, New Zealand (2007).
• February 20 2008 Sumatra earthquake 7.5 magnitude
• February 25 2008 Sumatra earthquake 7.3 magnitude. The quake was centered about 160 km (100 miles) south-southwest of Padang. The Pacific Tsunami Warning Center issued a local tsunami watch.
• March 21 2008 China earthquake 7.2 magnitude. The quake happened in Yutian County, Xinjiang, a remote region in the Kunlun Mountains far from any residential areas.
• March 29 2008 Sumatra earthquake 6.3 magnitude. The epicenter was about 175 miles (281 kilometers) south of Banda Aceh -- in a region hard-hit by the 2004 Indian Ocean earthquake. The Pacific Tsunami Warning Center issued warnings on the possibility of the quake triggering tsunamis on coasts near its epicenter.
• April 8 2008 earthquake 7.5 magnitude. The quake was in the southern Pacific Ocean, about 85 kilometers southwest of Vanuatu.
• May 12 2008 earthquake 8.0 magnitude about 60 kilometers northwest of Chengdu in the Sichuan province in China, killed over 65,000 people, expected to soar and China admits quake death toll could exceed 80,000.

Earthquakes in mythology and religion

In Norse mythology, earthquakes were explained as the violent struggling of the god Loki. When Loki, god of mischief and strife, murdered Baldr, god of beauty and light, he was punished by being bound in a cave with a poisonous serpent placed above his head dripping venom. Loki's wife Sigyn stood by him with a bowl to catch the poison, but whenever she had to empty the bowl the poison would drip on Loki's face, forcing him to jerk his head away and thrash against his bonds, causing the earth to tremble.

In Greek mythology, Poseidon was the god of earthquakes.

See also

• Catastrophe modeling
• Cryoseism
• Earthquake insurance
• Earthquake lights
• Earthquake engineering
• Earthquake weather
• Earthquake (1974 disaster film)
• Elastic-rebound theory
• Geophysics
• Hypothetical future disasters
• Interplate earthquake
• Intraplate earthquake
• Japan Meteorological Agency seismic intensity scale
• List of earthquakes
• List of all deadly earthquakes since 1900
• List of earthquakes by death toll
• List of tectonic plates
• Megathrust earthquake
• Meizoseismal area
• Mercalli intensity scale
• Moonquake
• Plate tectonics
• Richter magnitude scale
• Seismic scale
• Seismic wave
• Seismogenic layer
• Seismograph
• Seismology
• Shock (mechanics)
• Submarine earthquake
• Tsunami
• The VAN method

References

External links

apoplexy, breakup, cataclysm, climax, convulsion, diastrophism, disaster, fit, overthrow, paroxysm, quake, quaker, shake, shock, spasm, stroke, temblor, tidal wave, tremor, tsunami, upheaval