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[[File:Sanfranciscoearthquake1906.jpg|thumb|250px|

[[File:Sanfranciscoearthquake1906.jpg|thumb|250px|

[[San Francisco]], [[California]] earthquake, sometime in 1906]]

[[San Francisco]], [[California]] earthquake, sometime in 1906]]

An '''earthquake''' is when Earth's [[Plate tectonics|tectonic plates]] shake and move Earth's surface. Strong or high-magnitude earthquakes damage buildings.  

An '''earthquake''' is when Earth's [[Plate tectonics|tectonic plates]] shake and move Earth's surface. Strong earthquakes damage buildings.  

Disturbances in the earth's balance cause earthquakes. Different tectonic plates are slowly moving around each other. When they get stuck, tension builds up in them. Earthquakes occur when tectonic plates suddenly break free, so they start moving very quickly. The first point of an earthquake's rupture is called its [[:en:Hypocenter|hypocenter]] or focus. The epicenter is the point at ground level directly above the hypocenter.

Disturbances in the Earth cause earthquakes. Different tectonic plates are slowly moving. When they get stuck, tension builds up in them. Earthquakes occur when tectonic plates suddenly break free, so they start moving quickly. The first point of an earthquake's rupture is called its [[hypocenter]] or focus. The epicenter is the point at ground level directly above the hypocenter.

People who study earthquakes are called [[:en:Seismology|seismologists]]. Many earthquakes can occur in a small area in a short period of time. The sudden release of stress in the [[Plate tectonics|tectonic plates]] sends waves of energy that travel across the Earth. Seismology studies the cause, recurrence, type and magnitude of earthquakes.

People who study earthquakes are called [[seismologists]]. Many earthquakes can occur in a small area in a short period of time. The sudden release of stress in the [[Plate tectonics|tectonic plates]] sends waves of energy that travel through the Earth. Seismology studies the cause, recurrence, type and magnitude of earthquakes.

The effect of an earthquake can be measured with a [[seismometer]]. A seismometer detects the tremors of the earth and plots the tremors on a seismograph. The strength or magnitude of an earthquake can be measured using the Richter scale. The Richter scale was invented by Charles Francis Richter in 1935. The scale is numbered 0-10. A 2 on this scale is a tremor that is not easily recorded. And damage of size 5 (or more) in a wide area. The largest earthquake ever measured had a magnitude of 9.5.

The effect of an earthquake can be measured with a [[seismometer]]. A seismometer detects the tremors of the earth and plots the tremors on a seismograph. The strength or magnitude of an earthquake can be measured using the Richter scale. The Richter scale was invented by Charles Francis Richter in 1935. The scale is numbered 0-10. A 2 on this scale is a tremor that is not easily recorded. And damage of size 5 (or more) in a wide area. The largest earthquake ever measured had a magnitude of 9.5.

No one can tell when an earthquake will happen. But we know where earthquakes are likely to occur in the future, such as near fault lines. An earthquake under the ocean can create a huge wave called a tsunami. Tsunamis can also cause a lot of destruction.

No one can tell when an earthquake will happen. But we know where earthquakes are likely to occur in the future, such as near [[fault line]]s. An earthquake under the ocean can create a huge wave called a [[tsunami]]. Tsunamis can also cause a lot of destruction.

 

Landslides can also cause earthquakes.

== Zones ==

== Zones ==

== History ==

== History ==

Earthquakes sometimes hit cities and kill hundreds or thousands of people. Most earthquakes happen along the [[Pacific Ring of Fire]] but the biggest ones mostly happen in other places. [[Tectonics|Tectonically]] active places are places where earthquakes or [[volcanic eruption]]s are quite repeated.

Earthquakes sometimes hit cities and kill hundreds or thousands of people. Most earthquakes happen along the [[Pacific Ring of Fire]] but the biggest ones mostly happen in other places. [[Tectonics|Tectonically]] active places are places where earthquakes or [[volcanic eruption]]s are regularly repeated.

== Causes of an earthquake ==

== Causes of an earthquake ==

The boundaries between moving plates form the largest [[Fault (geology)|fault]] surfaces on Earth. When they stick, motion between the plates leads to increasing stress. This continues until the stress rises and breaks, suddenly allowing sliding over the locked portion of the fault. This releases the [[Potential energy|stored energy]] as [[shock wave]]s. The [[San Andreas Fault|San Andreas fault]] in [[San Francisco]], and [[Great Rift Valley|Rift valley]] fault in [[Africa]] are faults like this.

The boundaries between moving plates form the largest [[Fault (geology)|fault]] surfaces on Earth. When they stick, motion between the plates leads to increasing stress. This continues until the stress rises and breaks, suddenly allowing sliding over the locked portion of the fault. This releases the [[Potential energy|stored energy]] as [[shock wave]]s. The [[San Andreas Fault|San Andreas fault]] in [[San Francisco]], and [[Great Rift Valley|Rift valley]] fault in [[Africa]] are faults like this.

1. Volcanic Earthquakes: Earthquakes which are caused by volcanic eruptions are quite devastating. However, these are confined to areas of active volcanoes.

Earthquakes caused by volcanic eruptions can be quite devastating. However, these earthquakes are confined to areas around active volcanoes.

2. Collapse Earthquakes: In areas of intense mining activity, often the roofs of underground mines collapse and minor tremors take place. These are called collapse earthquakes.

 

Often the causes are not known, except in the most general terms. An example is the largest earthquake in the history of the United States: the [[1811–1812 New Madrid earthquakes]]. These are described as caused by very deep shifts in ancient rock formations. In other words, the cause is not known in detail.

 

In areas of intense mining activity, often the roofs of underground mines collapse and minor tremors take place. These are called collapse earthquakes.

== Earthquake fault types ==

== Earthquake fault types ==

{{main|Earthquake engineering}}

{{main|Earthquake engineering}}

Earthquake-proof buildings are constructed to withstand the destructive force of an earthquake. This depends upon its type of construction, shape, [[mass]] distribution, and [[wikt:rigid|rigidity]]. Different combinations are used. Square, rectangular, and shell-shaped buildings can withstand earthquakes better than [[skyscraper]]s. To reduce stress, a building's ground floor can be supported by extremely rigid, empty columns, while the rest of the building is supported by flexible columns inside the empty columns. Another method is to use rollers or rubber pads to separate the base columns from the ground, allowing the columns to shake parallel to each other during an earthquake.

Earthquake-proof buildings are constructed to withstand the destructive force of an earthquake. This depends upon its type of construction, shape, [[mass]] distribution, and [[rigid|rigidity]]. Different combinations are used. Square, rectangular, and shell-shaped buildings can withstand earthquakes better than [[skyscraper]]s. To reduce stress, a building's ground floor can be supported by extremely rigid, empty columns, while the rest of the building is supported by flexible columns inside the empty columns. Another method is to use rollers or rubber pads to separate the base columns from the ground, allowing the columns to shake parallel to each other during an earthquake.

To help prevent a roof from collapsing, builders make the roof out of light-weight materials. Outdoor walls are made with stronger and more reinforced materials such as steel or [[reinforced concrete]]. During an earthquake, flexible windows may help hold the windows together so they don't break.

To help prevent a roof from collapsing, builders make the roof out of light-weight materials. Outdoor walls are made with stronger and more reinforced materials such as steel or [[reinforced concrete]]. During an earthquake, flexible windows may help hold the windows together so they don't break.