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| | [[File:Japan quake sendai.jpg|thumb|200px|Japan quake 2011.]] | | [[File:Japan quake sendai.jpg|thumb|200px|Japan quake 2011.]] |
| − | An '''earthquake''' is when the [[Earth]] shakes, caused by [[plate tectonics|tectonic]] activity in an area after the release of stored [[energy]] from the [[rock]]. Earthquakes most commonly occur on tectonic plate boundaries, and also occur along [[fault|faults]] where previous movement has occurred. There are currently 500,000 detectable earthquakes in the world each year. | + | An '''earthquake''' is when the [[Earth]] shakes a perceptible amount. Earthquakes have been increasing over time:<ref>http://www.city-data.com/forum/alaska/1226039-increasing-frequency-major-earthquakes-2013-earthquake.html#ixzz2URWtQ6yV</ref> |
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| − | Earthquakes are a significant natural [[hazard]] to populations living in areas prone to them, and emergency responses to the hazard vary with economic development. The most powerful and destructive earthquakes occur at tectonic plate boundaries like the [[San Andreas Fault]].
| + | *from A.D. 1 to 1800 there was a major earthquake only about every 60 years. |
| | + | *in the 19th century there were about 31 earthquakes of magnitude 7 or higher, which averages to about a major earthquake every 3 years. |
| | + | *in the 20th century there were 222 such major earthquakes, or on average about one major earthquake every 6 months. |
| | + | *in the first decade of the 21st century (2001-2010) there were about 151 such major earthquakes, or on average more than 1 per month. |
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| − | The severity of earthquakes is measured using the [[Moment Magnitude scale]], which replaced the [[Richter scale]] in the 1970s. The largest quake ever recorded had a magnitude of 9.5; it struck Chile in 1960<ref>http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php</ref>. Technically the Moment Magnitude scale only measures the absolute magnitiude; the [[Mercalli scale]] is used to measure the felt magnitude - essentially how much the ground shakes over the epicentre of the quake. | + | Atheistic scientists often claim that earthquakes are caused by [[plate tectonics|tectonic]] activity in an area after the release of stored [[energy]] from the [[rock]]. But, in fact, earthquakes often do not occur on tectonic plate boundaries or [[fault|faults]] where previous movement has occurred. There are currently 500,000 detectable earthquakes in the world each year. |
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| | + | Earthquakes are a significant natural hazard to populations living in areas prone to them, and emergency responses to the hazard vary with economic development. The most powerful and destructive earthquakes occur at tectonic plate boundaries like the San Andreas Fault. |
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| | + | The severity of earthquakes is measured using the [[Moment Magnitude scale]], which replaced the [[Richter scale]] in the 1970s. The largest quake ever recorded had a magnitude of 9.5; it struck Chile in 1960.<ref>http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php</ref> Technically the Moment Magnitude scale only measures the absolute magnitiude; the [[Mercalli scale]] is used to measure the felt magnitude - essentially how much the ground shakes over the epicentre of the quake. |
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| | ==Causes of Earthquakes== | | ==Causes of Earthquakes== |