What is an Earthquake?

Earthquake refers to a sudden violent shaking and vibration of the earth surface resulting from underground movement along a fault plane or from volcanic activity. Earthquakes can cause serious destruction to property, injury to people and even kills. It happens when there is sudden movement or breaking of the tectonic plates.

Tectonic plates are huge rock pieces within the earth’s crust. The plates are usually marked by fractures or fault lines formed when the plates tear apart or slide or collide past each other. This results in a change of the earth’s interior masses which send out powerful shock waves with enough force to alter the surface of the earth. The shock waves can thrust up cliffs and open huge cracks on the ground leading to an earthquake event.

According to Wikipedia, “An earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth’s crust that creates seismic waves. Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.


Causes of Earthquake

Almost every year, earthquakes are recorded in various parts of the world. Since the shear and tear forces are always constant within the earth’s plate tectonics, earthquakes can occur at any time. Thousands of minor tremors often take place just because of these constant movements.

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Earthquakes develop simply when the underground rocks (plate tectonics) unexpectedly break along fault lines. Earthquakes are measured using observations from seismometers. Earthquakes are, thus, caused by tectonic plate movements, volcanic activity or underground explosions.

  1. Plate Tectonic Movements

Plate tectonic movements cause the majority of the earthquakes. The movements occur because the plates float on the hotter and denser rock of the mantle. Consequently, these plates are usually in constant movement – past or from each other within the earth’s crust.

When these plates (rocks) break or slide past each other at boundaries known as fault lines, they release shock waves. The shock waves are results of the energy stored in the earth crust due to the underground pressure of the earth’s inner core.

Aside from the shock waves, the tectonic plate movements snag on coarse patches of rock and pull at entangled sections that further crack the earth’s crust, producing more faults near the boundaries of the plates. After some period, the build up energy and movement generates great tensions in the plates and builds pressure on the fault lines. The intense pressure from the shock waves makes the fault lines to collapse, and the plates move over, up and against each other.

As a result, an earthquake occurs when the pressure build up along the fault lines becomes stronger than the force holding the tectonic plates together. This happens when the rocks (plates) suddenly rip apart or fall on either side at ultrasonic speeds releasing the pent-up pressure which moves outward in all directions.

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When it reaches the earth’s surface, an earthquake occurs which is in the form of ripples (seismic waves) of escaping energy. The rippling effect is what causes the rapid and violent vibration of the earth surface – earthquake, shaking and tearing everything on it including the earth surface itself, structures, and houses.

Majority of the earthquakes originate along the edges of the plates and occur in some regions more frequently than others. The National Geographic reports that 80% of the earthquakes occur around the edge of the Pacific plate in Japan, Canada, USA, Papua New Guinea, South America, and New Zealand. Earthquakes severity also differs depending on the amount of stored energy released and the extent of faulting. Geologists believe there is no regularity in the occurrence of earthquakes.

Aftershocks may as well be experienced after earthquake events. Aftershocks refer to smaller shock waves that result from the adjustment of the crust after the principal shock. The aftershocks can worsen the aftermath of the disastrous earthquake outcomes.

  1. Volcanic Activity

Apart from tectonic plate movements, volcanic activity can significantly cause massive earthquakes. Earthquakes normally accompany escaping magma as it rises to the crust during a volcanic eruption. This is mainly due to the sudden displacement and shaking of underground rocks.

Volcanic activity also creates fault lines and underground disturbances that can instigate the sudden ripping or falling of the tectonic plates, thus, releasing the pent-up pressure which moves outwards in all directions.

  1. Underground Explosions

Seismic waves (wave shocks) similar to the ones causing earthquakes can be generated by underground explosions. These explosions can be as a result of underground mining or during the construction of railroads, subways, or underground tunnels. However, some of the seismic waves produced by these activities are not as strong as those produced by real earthquakes.

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Per se, they can only be felt within the adjacent areas. On the other hand, underground nuclear tests are known to be very dangerous and can produce powerful seismic waves similar to that of a natural earthquake. For this reason, underground nuclear tests have been banned globally.


Sonia Madaan is a writer and founding editor of science education blog EarthEclipse. Her passion for science education drove her to start EarthEclipse with the sole objective of finding and sharing fun and interesting science facts. She loves writing on topics related to space, environment, chemistry, biology, geology and geography. When she is not writing, she loves watching sci-fi movies on Netflix.