why do earthquakes occur?

Answer 1

How Earthquakes Occur (Java animation or static images)
http://projects.crustal.ucsb.edu/understanding/

Answer 2

Earthquakes almost always are the result of tectonic activity, meaning they occur because of the movement of the earth's tectonic plates, which make up the earth's crust. Since we humans live on these plates, which in turn float on the earth's mantle, it follows that any disturbance on these plates must be felt by us as earth-shattering events- earthquakes. Hence earthquakes are most common at the places where these tectonic plates meet, called fault lines. The so-called pacific rim of fire, encompassing Indonesia, the Philippines, Japan and the west coast of the Americas represents an area of intense tectonic activity - volcanic eruptions and earthquakes,

Sometimes volcanic eruptions also cause earthquakes, but then volcanoes too are manifestations of geothermal energy.

Answer 3

Earthquakes occur due to movement of tectonic plates which build up the earth's crust. From the start of this world to till date, Earth's tectonic plates are continuously on the move. This movements generally occur due to the underground convection movements of magma material. When these plates collide with each other or slides over one another, it causes vibrations of huge magnitudes(measured in Richter scale), and these vibrations result in the occurence of earthquakes. The soure from which earthquakes occur is known as epicentres.

Answer 4

The world is of plates known as sea plates & land plates. There are 7 big plates & 23 small plates . These are seted like jig-saw-fit . whnever the core of the earth melts (it is a inner process) the some plates comes closer some makes distant to each other . while this process we fill the vibration on the surface & when the vibration goes up of 6.0 in measurement through the rector scale it is known as EARTHQUAKE.

Answer 5

when two or more rocksbeneath the earth strikes or moves over each other the shaking of earth takes place this is termed as earthquakes.

Answer 6

earth quakes occur due to the dislocation of the tectonic plates underneath the land.these dislocations may often be caused due to the sudden valconic eruptions that results due to suppression over a long period of time and hence is often accompanied by valconic eruption

Answer 7

In earth there are some plates.when theses collide with 1 another EARTHQUAKES and TSUNAMI'S occur.

Answer 8

Tectonic plate movement mostly.

Answer 9

An earthquake is a phenomenon that results from the sudden release of stored energy in the Earth's crust that creates seismic waves. At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground and sometimes tsunamis, which may lead to loss of life and destruction of property.

Earthquakes may occur naturally or as a result of human activities. 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.

Types of earthquakes
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 heat in the Earth's mantle and core. Plate boundaries grind past each other, creating frictional stress. 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, the elastic strain energy is released and seismic waves are radiated, thus causing an earthquake. This process of strain, stress, and 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 and is converted into heat. Therefore, earthquakes lower the Earth's available potential energy, though these losses are negligible.[1]

Earthquakes occurring at boundaries of tectonic plates are called interplate earthquakes, while the less frequent events that occur in the interior of the lithospheric plates are called intraplate earthquakes.

The majority of tectonic earthquakes originate at depths not exceeding a few tens of kilometers. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, earthquakes may occur at much greater depths (up to hundreds of kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. Deep focus earthquakes are another phenomenon associated with a subducting slab. 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.[2]

Earthquakes may also occur in volcanic regions and are caused by the movement of magma in volcanoes. Such quakes can be an early warning of volcanic eruptions.

A recently proposed theory suggests that some earthquakes may occur in a sort of earthquake storm, where one earthquake will trigger a series of earthquakes each triggered by the previous shifts on the fault lines, similar to aftershocks, but occurring 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.

Induced earthquakes
Some earthquakes have anthropogenic sources, such as extraction of minerals and fossil fuel from the Earth's crust, the removal or injection of fluids into the crust, reservoir-induced seismicity, massive explosions, and collapse of large buildings. Seismic events caused by human activity are referred to by the term induced seismicity. They however are not strictly earthquakes and usually show a different seismogram than earthquakes that occur naturally.

A rare few earthquakes have been associated with the build-up of large masses of water behind dams, such as the Kariba Dam in Zambia, Africa, and with the injection or extraction of fluids into the Earth's crust (e.g. at certain geothermal power plants and at the Rocky Mountain Arsenal). Such earthquakes occur because the strength of the Earth's crust can be modified by fluid pressure. Earthquakes have also been known to be caused by the removal of natural gas from subsurface deposits, for instance in the northern Netherlands. The world’s largest reservoir-induced earthquake occurred on December 10 1967 in the Koyna region of western Maharashtra in India. It had a magnitude of 6.3 on the Richter scale. However, the U.S. geological survey reported the magnitude of 6.8.[3]

The detonation of powerful explosives, such as nuclear explosions, can cause low-magnitude ground shaking. Thus, the 50-megaton nuclear bomb code-named Ivan detonated by the Soviet Union in 1961 created a seismic event comparable to a magnitude 7 earthquake, producing the seismic shock so powerful that it was measurable even on its third passage around the Earth. In an effort to promote nuclear non-proliferation, the International Atomic Energy Agency uses the tools of seismology to detect illicit activities such as nuclear weapons tests. The nuclear nations routinely monitor each other's activities through networks of interconnected seismometers, which allow to precisely locate the source of an explosion.

Sports games have been known to inadvertently produce microearthquakes. This phenomenon was first seen in 1988 with the Earthquake Game at Louisiana State University, in which fans stamped their feet and jumped up and down vigorously enough to have the effect register on the campus seismograph.

Earthquakes happen every day around the world, but most of them go unnoticed and cause no damage. Large earthquakes however can cause serious destruction. They may be caused by the ground shaking, a tidal wave or tsunami, fire or by gas or petrol leaks. Most large earthquakes are accompanied by other, smaller ones that can occur either before or after the 'main shock'. The power of an earthquake covers a large area, but in a very large earthquake, it can even cover the whole planet. Scientists can locate the point from which the earthquake started. That point is called its focus or hypocenter. The location on the surface of the earth directly above the hypocenter is known as the epicenter.

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Answer 10

Because.