Different Types Of Earthquakes

Earthquakes, caused by the propagation of seismic waves, are tremendous natural forces which, since time immemorial, have caused a lot of devastations. These seismic waves are produced by the sudden release of energy amassed in the earth’s crust. Earthquakes occur along the regions of geological faults and narrow zones, due to the corresponding movement of the rock masses. The most sensitive or earthquake prone regions of the world lie at the fringes of the gigantic tectonic plates that constitute the Earth’s crust. However, very little was known about the causes and types of earthquakes, until the 20^th century. But, with the evolution of the ‘seismology’, scientists have been able to understand the nature of this great devastating force more and more. Earthquakes often occur in regions away from fault lines. However, earthquakes don’t always occur naturally and there are several manmade causes also for their occurrence. Scroll down and read all the major types of earthquakes and their causes.

Different Types Of Earthquakes

Tectonic Earthquakes

The earth’s crust comprises of gigantic fragments or plates, called tectonic plates. These plates can slide over the plastic aesthenosphere, uppermost layer of the mantle.
The tectonic plates have a considerable degree of freedom and can slide in any direction, away from each other, towards each other and even past each other; it is this third movement which causes the tremors on earth’s surface.
American geologist Harry Fielding Reid explained the tectonic earthquakes for the first time in his ‘elastic rebound theory’, after the San Andreas Fault ruptured in 1906 and caused the infamous San Francisco earthquake.
The movement of the tectonic plates is the most common cause of earthquakes all over the world.
There are a number of crustal plates, which have been split into several smaller plates. These plates are around 80 kilometers in thickness, and are constantly moving. The speed of their movement has been found to be somewhere around 10 to 130 mm per year.
However, the nature of their movement is not symmetrical and many geological formations such as mountains and rift valleys, and phenomena such as volcanoes, earthquakes, faulting, etc. are due to different types of interactions at plate boundaries.
The intensity of these earthquakes can be extremely high and has been responsible for severe devastations throughout the history of earth.

Volcanic Earthquakes

Volcanic earthquake are caused by volcanic eruptions and are not a very common occurrence; these are at least much less frequent than the tectonic earthquakes.
Volcanic earthquakes can be further divided into two categories, viz., volcanic tectonic earthquakes and long period volcanic earthquakes.
The earthquake which follows a volcanic eruption is known as the volcanic tectonic earthquake.
Typically every volcanic eruption leads to a great release of magma which creates a great vacant space which is then filled in by a great mass of rocks. The movement of these rocks towards the empty space creates shock waves which propagate across the earth’s surface.
It also happens that the lava which gets discharged during any volcanic eruption falls on the very outlet from which it is ejected. It seals the vent and an enormous pressure is created. However, the closure created by the Lava can’t sustain the pressure for long and soon a great explosion follows. This explosion causes a long period volcanic earthquake which often ranks high on the Richter scale.
A long period of volcanic earthquake follows a great volcanic eruption. After a volcanic eruption, the magma undergoes a change of heat, which begets seismic waves resulting in an earthquake.

Collapse Earthquakes

Much inferior in magnitude as compared to the two aforementioned earthquakes, a collapse earthquake occurs in the regions around underground mines.
Also known as the mine burst, this type of earthquake is stirred due to the release of pressure stored in the rocks. Due to this outburst of pressure, the roof of the mine or cavern collapses, releasing seismic waves which cause the tremors.
This type of small scale earthquake can be frequently felt in areas where there are underground mines.

Explosion Earthquakes

An explosion earthquake is caused by nuclear and chemical devices. Underground nuclear explosions release an enormous amount of energy which creates powerful seismic waves in the area around where the tremors can be felt.
In the 1930s, during the nuclear tests in America, and in 1998, during the nuclear tests in Pokharan, India, many small villages and towns in the surrounding regions felt powerful quakes.

Most natural earthquakes are caused by the movement of the tectonic plates. However volcanic eruptions have also been responsible for some of the major earthquakes throughout the history of the earth. And nowadays, even manmade nuclear inventions can trigger this phenomenon.

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