We all, at some point of our life, have been through this disaster. Some of us may have witnessed small earthquakes, such as an earthquake of 2.6 magnitude, while others may have been through more violen? ones, such as magnitude more than 7.6. Let’s find out how earthquakes occur.
This post is only an introduction to earthquakes, but I will be posting about induced earthquakes or human induced earthquakes soon, I.A. I will try my best to keep this simple and informative. I will avoid overloading you with earthquake facts and figures.
An Earthquake is a series of underground shock waves and movements on the earth’s surface caused by natural processes within the earth’s crust.
Earthquakes usually occur when the rocks underground suddenly breaks along a fault. This sudden release of energy cause the seismic waves that make the ground shake.
Earthquakes usually occur where plates meet. When two blocks of rocks or two plates start to move away from each other, frictional force prevents or hinders this process. Due to this friction, the rocks break. The plates or rocks keep sliding against each other until all the built in stress is released.
The spot underground where the rock first breaks is called the focus (hypocenter) of the earthquake. The place right above the focus (on top of the ground) is called the epicenter of the earthquake.
How do we feel earthquake?
We feel earthquake through due the seismic waves. Seismic waves are of two main types, body waves and surface waves.
Body waves are of two types, primary and secondary waves. Body waves are the waves which are first sensed at a seismic station.
Primary waves are compressional waves (they move through compression and relaxation, just like sound waves), while secondary waves are sheer waves. P-waves are the first to arrive at a station and they can propagate through fluids as well. These are the waves that animals sense before an earthquake (such as dogs sense earthquake before it actually happens). 
Surface waves are the waves that are responsible for the damages during an earthquake. There are two types of surface waves, Love waves and Rayleigh waves.
Earthquakes can be measured on two main basis. One scale is based on the magnitude of earthquake, called the Richter Scale, while the other scale is based on the level of damage that an earthquake causes, that is called Mercalli scale.
If you want more information about earthquakes, click here to open this amazing file I found.
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