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The earth consists of four major sections: the inner core, outer core, mantle, and crust. The crust is the top-most part, but is not a single piece, rather, it is made up of several pieces, like a jig-saw puzzle. The pieces keep moving gradually, slipping past one another and colliding with each other. These pieces are referred to as tectonic plates. The points at which tectonic plates separate (plate boundaries) contain numerous faults and most earthquakes occur along the boundaries due to the numerous faults.
An earthquake originates from the rapid discharge of energy from the earth’s core that generates seismic waves. It is measured using readings from a seismometer. The energy that causes earthquakes can originate from different forms of earth movements, these are generally termed as the causes of earthquakes and are outlined below:
Naturally occurring Quakes
Earthquakes can occur naturally when tectonic plates slip or slide past one another rapidly along a fault plane. Once the plates slide past one another, continuous relative movement between the plates causes an increase in stress and hence, piles up strain energy around the two plates.
The process continues until stress energy has reached a level in which it can escape through the fault line, suddenly releasing stored energy around the plates. The trapped energy is produced as a mixture of trapped seismic waves, frictional heating of the fault line, and splitting of rocks. This energy is so intense that it causes earthquakes (Greene II & Burnley, pp. 434).
These are earthquakes that do not occur on the plate boundaries, rather, they take place within the continental lithosphere. This form of earthquake is more extensive than that caused by movement of plate tectonics. All tectonic plates have interior stress zones that originate from their contact with nearby plates and sedimentary addition or removal (e.g. glaciation). These stresses may be adequate to create a weakness along existing fault planes, producing an intraplate earthquake (Nettles and Ekström, pp. 480).
Earthquakes also occur due to volcanic activity. Such an earthquake is caused by a combination of tectonic plate movement and movement of magma in the earth’s crust. This form of earthquake can be so severe and can be a form of early warning of an impending volcanic eruption in the area.
For example, the Mount. St. Helens eruption that occurred in 1980 in Washington was preceded by severe earthquakes. Movement of magma in the earth’s crust causes violent movements and this can cause the movement of small plates and this, in turn, causes movements on the earth’s surface.
Continental drift is the motion of the Earth’s tectonic plates (or planets) relative to each other. The Continental drift theory was proposed by Alfred Wegener, who proposed that nearly 200 million years ago, a supercontinent known as Pangaea split up into the current continents.
This splitting occurred during the Jurassic era, and by the end of the Cretaceous era, the tectonic plates were splitting and forming the present continents. The theory receives support from similar fossil records that have been found in different continents around the world (Romm, pp. 407).
The continental drift process led to the formation of the six planets that we have currently. Besides, the boundaries between the tectonic plates experience earthquakes more than any place on earth, hence, the continental drift can be said to have contributed to the quakes that are experienced today.
Greene II, Harry and Burnley, Pamella. A new self-organizing mechanism for deep – focus earthquakes. Nature 341 (6244), 1989. 733–737.
Nettles, Meredith, and Ekström, Goran. Glacial Earthquakes in Greenland and Antarctica. Annual Review of Earth and Planetary Sciences, 38 (1), 2010. 467–491.
Romm, James (February 3, 1994), A New Forerunner for Continental Drift. Nature 367, 1994. 407–408.