Earthquakes occur when an underground rock breaks along a fault line.
The Earth is made up of layers. The inner most layer is called inner core; the layer outside of that is called the outer core. The outer core is surrounded by the mantle, which in turn is covered by the crust, which is the outer most layer. The crust included the surface of the Earth, which is about 100 km deep, and on which we reside.
There are two main types of earthquake: one that occurs in the inner core. The reason behind these earthquakes is still not conclusively known. These rarely have an impact on the surface, in fact most people don’t even realize that they have occurred. The second kind of earthquakes is the one that we are most familiar with. They are also the ones that cause damage to the surface of the earth.
The earth’s surface is made up of layers, one stacked on the other. The lines where one layer coincides with the other is called fault lines. These layers are often pushing and pulling against one another, which erodes them over time. Eventually it happens, that after a lot of pulling and pushing, these layers break at the fault line. This break is what causes an earthquake. It also releases a lot of energy. The centre of the earthquake, i.e. where the earthquake occurs, is called a focus, and the point directly above it, on the surface of the earth is called an epicenter.
Earthquakes may also occur when there is an explosive eruption of a volcano. However, these kinds of earthquakes are much rarer than the ones caused by the tectonic plates. Earthquakes can also be man-made. These occur when there are nuclear bomb blasts, or blasting for mining, clearing debris, or making new roads. However, these are usually not counted as an earthquake. In order for it to be considered as an earthquake, it should be of natural origin.
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