P4+-+Earthquakes

An Earthquake is the release of energy from within the Earth's Crust that creates seismic waves. The seismicity refers to the measure of the earthquakes frequency, type and size. Earthquakes are measured by a siesmograph, a device which aso records informatio about earthquakes. Earthquakes are meausred on a scale called moment magnitude, a very weak magnitude earthquake would be a 3 and a very strong earthquake would be a 7. An Earthquake shakes and sometimes diplaces the ground. The word earthquake is used to describe any seismic event, whether caused by a person or naturally occurs.
 * __Earthquakes__**

__Aftershocks__ An aftershock is a smaller earthquake that occurs after an earthquake and is usually always in the same region as the earthquake. If an aftershock is larger than the original quake, the original quake is a foreshock. Aftershocks form around the displaced fault line.

__Foreshocks__ A foreshock is a small earthquake that occurs before a larger siesmic event.

__Occurance__ 500,000 earthquakes occur every year and only about 100,000 are felt. The UK has Earthquakes ranging from 3.7-4.6 every year. There have been 18 major earthquakes (7.5-7.9) every year and there has been 1 great earthquake (8.0+) per year. Most of earth's earthquakes take place in a horse shoe shap about 40,000km long.

Earth's Plates