Size and frequency of occurrence
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Unbalanced scales
Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in Guatemala. Chile, Peru, Indonesia, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, and Japan, but earthquakes can occur almost anywhere, including New York City, London, and Australia.[6] 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, but this is because of the vast improvement in instrumentation, rather than an increase in the number of earthquakes. 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.[7] In recent years, the number of major earthquakes per year has decreased, although this is thought likely to be a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the USGS.[8]
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.[9][10] Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains. Humans can cause earthquakes for example by constructing large dams and buildings, drilling and injecting liquid into wells, and by coal mining and oil drilling.[11]
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.[12][13][14]
Effects/impacts of earthquakes
1755 copper engraving depicting Lisbon in ruins and in flames after the 1755 Lisbon earthquake. A tsunami overwhelms the ships in the harbor.
1755 copper engraving depicting Lisbon in ruins and in flames after the 1755 Lisbon earthquake. A tsunami overwhelms the ships in the harbor.
Smoldering after the 1906 San Francisco earthquake.
Smoldering after the 1906 San Francisco earthquake.
Earthquake damage in Anchorage, Alaska (1964).
Earthquake damage in Anchorage, Alaska (1964).
Earthquake damage in Mexico City (1985).
Earthquake damage in Mexico City (1985).
Earthquake damage in Armenia (1988).
Earthquake damage in Armenia (1988).
A section of the Cypress viaduct collapsed during the Loma Prieta Earthquake (1989).
A section of the Cypress viaduct collapsed during the Loma Prieta Earthquake (1989).
Kaiser Permanente Building destroyed in the Northridge Earthquake (1994).
Kaiser Permanente Building destroyed in the Northridge Earthquake (1994).
Damage in Great Hanshin earthquake (1995) in Kobe, Japan.
Damage in Great Hanshin earthquake (1995) in Kobe, Japan.
Chūetsu earthquake (2004).
Chūetsu earthquake (2004).
Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion. (December 2007)
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[15]. 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[16].
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
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.[17]
In Greek mythology, Poseidon was the god of earthquakes.[18]
See also
Look up earthquake in Wiktionary, the free dictionary.
* Catastrophe modeling
* Cryoseism
* Earthquake insurance
* Earthquake lights
* Earthquake engineering
* Earthquake weather
* Earthquake (1974 disaster film)
* Geophysics
* Hypothetical future disasters
* Interplate earthquake
* Japan Meteorological Agency seismic intensity scale
* List of earthquakes
* List of all deadly earthquakes since 1900
* List of earthquakes by death toll
