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4. Questions - Got a question about Earthquake then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

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6. Returns - still worried that even after all of the above your Earthquake wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

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8. Security - check for the yellow padlock on the Earthquake site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Earthquake, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Earthquake, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

An earthquake is the result of a sudden release of energy in the Earth's crust (geology) that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The Moment magnitude scale of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude scale 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, but also by volcanic activity, landslides, mine blasts, and nuclear experiments.

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

s, 1963–1998



Naturally occurring earthquakes

Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patchwork of plates in slow but constant motion caused by the release to space of the heat in the Earth's mantle and core. The heat causes the rock in the Earth to become flow on geological timescales, so that the plates move slowly but surely. Plate tectonics boundaries lock as the plates move past each other, creating frictional Stress (physics). When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's Crust (geology), energy is released as a combination of radiated elastic Strain (materials science) 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 (geology) 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 convection flow of heat out from the Earth's deep interior.

The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In Subduction, 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 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.

Some earthquakes occur in a sort of earthquake storm, where earthquake strike a fault in clusters, each triggered by the previous shifts on the fault lines, similar to aftershocks, but occurring on adjacent segments of fault, sometimes years later, 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 Small 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, the Azores in Portugal, New Zealand, Greece and Japan.{{cite web| url=http://earthquake.usgs.gov/ | title=Earthquake Hazards Program | publisher=[USGS | accessdate=2006-08-14 --> Large earthquakes occur less frequently, the relationship being Gutenberg-Richter law; 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:



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.{{cite web| title=Common Myths about Earthquakes | url=http://earthquake.usgs.gov/learning/faq.php?categoryID=6&faqID=110 | publisher=[USGS | accessdate=2006-08-14 --> 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.{{cite web| title=Earthquake Facts and Statistics: Are earthquakes increasing? | url=http://neic.usgs.gov/neis/eqlists/eqstats.html | publisher=[USGS | accessdate=2006-08-14 -->

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 Pacific Ring of Fire, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate.{{cite web| title=Historic Earthquakes and Earthquake Statistics: Where do earthquakes occur? | url=http://earthquake.usgs.gov/learning/faq.php?categoryID=11&faqID=95 | publisher=[USGS | accessdate=2006-08-14 -->{{cite web| url=http://earthquake.usgs.gov/learning/glossary.php?termID=150 | title=Visual Glossary - Ring of Fire | accessdate=2006-08-14 --> Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.

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 Richter magnitude scale, 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 electric 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 earthquake 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.

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

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.

Preparation for earthquakes

Specific fault articles

Major earthquakes Pre-20th century

claimed over 25,000 lives and left 500,000-plus homeless.

20th century

21st century El Comercio Peru | title = El Comercio Peru | url = http://www.elcomercio.com.pe/ediciononline/HTML/olecportada/2007-08-15/olecportada0419459.html-->

Earthquakes in mythology and religion In Norse mythology, earthquakes were explained as the violent struggling of the god Loki. When Loki, Aesir 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.Prose Edda by Snorri Sturluson

In Greek mythology, Poseidon was the god of earthquakes.http://www.theoi.com/Olympios/Poseidon.html

In Christian mythology, certain saints were invoked as patron saint against earthquakes, including Saint Gregory Thaumaturgus, Saint Agatha, Saint Francis Borgia, and Saint Emygdius.http://www.catholic-forum.com/saints/pst00245.htm

See also

References External links Educational

Seismological data centers Europe

United States

Seismic scales

Scientific information | url=http://simscience.org/crackling/Advanced/Earthquakes/GutenbergRichter.html | title=Earthquake Magnitudes and the Gutenberg-Richter Law | publisher=http://simscience.org/index.html SimScience | accessdate=2006-08-14 -->
 

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