An earthquake is the shaking or trembling movement of the earth's crust. This can be caused by volcanic eruption deep within the earths crust, or the collision of the earth's continually moving plates. When the earths crust vibrates, shock waves ripple out to the earth's surface. These waves can be measured using a seismograph and can range from being barely noticeable to viciously destructive.
There are three types of earthquakes, volcanic, tectonic and artificial. .
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Tectonic earthquakes are caused by collisions of the plates, which make up the crust of the earth. These earthquakes occur at the boundaries of the plates, where they slide along each other causing a build up of friction and pressure, until a sudden release of energy results in an earthquake. This will also have the same release of energy, if the plates are in a head on collision. Of the three, Tectonic earthquakes are the most devastating, and they account for almost half of the world's destructive earthquakes.
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Volcanic earthquakes are generally much smaller than tectonic ones. They are caused when magma flows upward and fills the chambers beneath a volcano. The sides and tops of the volcano expand with pressure and result in numerous small earthquakes. Volcanic earthquakes are often the forerunner for volcanic eruptions.
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Sometimes earthquakes occur as a result of man, for example when a new reservoir is filled. They are very rare and relatively harmless when compared to those caused by nature.
You can measure the intensity of earthquakes by using the Richter scale. Which is a scale that runs from one to nine, each number is an increase of ten times than the number before it. Therefore, a 7.0 earthquake is ten times more powerful than a 6.0 and 100 times more powerful than a 5. This scale measures the amount of energy released at the focus of an earthquake.
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There are no reliable methods as yet for predicting when earthquakes will happen, although some countries such as China and the U.