Earthquake phenomena explained with the help of GIFs

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Earthquakes are a natural hazard and they are referred to as the movements within the Earth’s crust that occur due to the stress that builds up at points of weakness and causes rock deformation. Many people believe that earthquakes happen only when the massive tectonic plates of the Earth move against each other. The shifting and colliding of these plates is certainly the main cause of earthquakes, but volcanoes, falling meteors and other occurrences can also cause the ground beneath your feet to move. Featured are some Earthquake related animations with their relevant descriptions.

Earthquakes due to Faults

Image Courtesy: www.uwgb.edu

Most earthquakes occur at plate boundaries. Earthquakes associated with faults on plate boundaries are called interplate earthquakes. About 5% of earthquakes are intraplate earthquakes and occur in the center of a tectonic plate.

-Along Normal Fault

Image Courtesy: josealvarezgomez.wordpress.com

When the hanging wall drops down due to extensional forces, an earthquake occurs with the formation of a normal fault.

-Along Reverse Fault

Image Courtesy: geology.ar.gov

The animation shows that as the hanging wall moves up with respect to the footwall, it leads to the formation of a reverse fault. You can also see that as the stress is released from the red point called the focus, waves propagate through the Earth’s surface resulting in an earthquake.

-Along Strike-Slip Fault

Image Courtesy: openhazards.com

Strike-slip faults have a different type of movement than normal and reverse fault.  In these faults the fault plane is usually vertical, so there is no hanging wall or footwall. The forces creating these faults are lateral or horizontal, carrying the sides past each other. As you can see in the animation that as the sides slips past each other, they result in an earthquake. The slip occurs along the strike, not up or down the dip.

While tectonic plates move at a constant rate, most faults do not. When a fault does moves slowly without rupture, it is said to “creep.” Evidence of creep can sometimes be seen in slightly displaced buildings or a jog to the left or right in a sidewalk. Most faults do not slip much at all most of the time, and when they do slip, they cause earthquakes. A typical fault with a slip rate of 2 mm/yr might have one earthquake approximately every 100 years that creates about 0.2 meters of displacement in a matter of seconds.

Earthquakes due to Volcanic Eruptions

Image Courtesy: vulcan.fis.uniroma3.it

A volcano tectonic earthquake is an earthquake induced by the movement (injection or withdrawal) of magma. The movement results in pressure changes in the rock around where the magma has experienced stress. At some point, the rock may break open which leads to magma eruption. The animation shows the eruption of Mount Vesuvius and the subsequent earthquakes that destroyed the cities of Pompei, Herculaneum, Oplonti and Stabiae.

Earthquakes due to Induced Seismicity

Image Courtesy: motherjones.com

Induced seismicity refers to typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. In the past several years, some energy technologies that inject or extract fluid from the Earth, such as oil and gas extraction and geothermal energy development, have been found or suspected to cause seismic events.  The animation shows how the disposal of waste through injection well leads to a seismic event.

Underwater Earthquakes

Image Courtesy: mail.colonial.net

Underwater Earthquakes lead to Tsunami's. The displaced rock along an underlying fault causes a bulge in the ocean waves which leads to the formation of a tsunami as shown in the animation.

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