What are the common causes of earthquakes? The causes of earthquakes can be very different, but usually they happen because of the movement of the earth’s plates.
The ground is in motion. Usually it cannot be felt because it is very slow. The earth’s crust—the outermost layer—is divided into what scientists simply call “tectonic plates,” or simply plates. Modern technology has enabled geologists to map the boundaries of the earth’s plates with a high degree of accuracy.
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What are the Common Causes of Earthquakes
The plates drift slowly on top of the viscous mantle. The crust is not as dense as the mantle and therefore floats on it much like a wooden board will float on water, which is denser than wood. The rate of drift is typically slow—measured in centimeters per year. There are eight large, major plates, and many smaller ones.
As they move about, plates often meet the resistance of another plate. The result of this resistance sometimes causes fracturing of the crustal rocks—faults—creating an earthquake.
Thousands of quakes are recorded daily, but most are not felt because they do not involve large scale fracturing and because they may be quite deep – perhaps over 400 miles deep.
Minor quakes are recorded by devices called seismographs, which are anchored deep in the earth’s crust. Several Internet sites offer daily reports of earthquake activity and informations about the causes of earthquakes around the world.
Sometimes the Earth’s Plates are the Causes of Earthquakes
As long as the plates move past one another, there is little cause for concern, but sometimes they become jammed against each other. This sticking causes stress to build up until the strength of the rocks is suddenly overcome and a fracture occurs.
If the depth of the fracture is less than about 40 miles, the energy released will be felt on the earth’s surface. The forces can cause deformities in the surface as cracks—fissures—open up.
In coastal regions, the shaking earth may mix with water and lose its ability to support structures, causing buildings to partially sink or tip over. Structures may simply collapse because of the enormous energy released by the sudden fracture or slipping that overwhelms architectural integrity.
If a plate is thrust upward, the earth’s surface may transmit ripples like waves on a pond. As these waves move beneath buildings they destroy foundations causing collapse. Objects and people can be literally tossed upward as a result of a violent quake.
Boundaries are not all the Same
Where plates meet, they may simply try to slide past each other. These are called transform boundaries. Plates may collide as they move toward each other, forcing one plate under the other at a convergence boundary.
Finally, plates may move apart at divergent boundaries and pull the surface apart, creating rift valleys. About ten percent of earthquakes occur away from boundaries. These are known as intraplate boundaries. The causes of earthquakes are well understood.
Earthquakes are frequent, but few are felt. They are a normal result of the movement of the earth’s crust beneath us. The crust is divided into eight major plates, which meet at different types of boundaries.
When the plates impede each other’s movement, stress builds up until the rocks break, releasing enormous amounts of energy which can shake the earth’s surface violently.
Read about the difference between earthquakes and tremors in our ecology category. Earthquakes can also lead to volcanic erruptions, which is another interesting topic to read about.
