How do earthquake occur?

We all have heard about natural disasters that devastate lives, property and cause overall adverse effects. Out of them, one of the most common ones is an earthquake.

An earthquake is what happens when two blocks of the earth suddenly slip past one another.

The surface where they slip is called the fault or fault plane.

The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.
 
Sometimes an earthquake has foreshocks.

These are the smaller earthquakes that happen at the same place.

They occur before the larger earthquakes occur.

It is impossible to predict if a larger earthquake is coming after a foreshock as we cannot differentiate between a foreshock and an actual earthquake. 
 
The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow.

These are smaller earthquakes that occur afterward in the same place as the mainshock.

Depending on the mainshock, the aftershocks may last for days, weeks, months, and sometimes even years. 

What causes earthquakes and where do they happen?

One of the most important questions about an earthquake is how they occur.

For understanding how they occur, first, we have to understand the four major layers of the planet.

The earth has four major layers: the inner core, outer core, mantle, and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet.
 
However, this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth.

Moreover, these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other.

These puzzle pieces are called tectonic plates.

The edges of these plates are called plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults.

As these edges are quite rough, they get stuck while the rest of the plate keeps moving.

Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.

 
Why does the earth shake when there is an earthquake?

Furthermore, who does the earth feel tremors and shakes during an earthquake?

While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up.

When the force of the moving blocks finally overcome a large amount of friction of the jagged edges of the faults and it unsticks, all the potential energy stored is released. 
 
The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond.

These waves shake the earth as they move through it, and when the waves reach the earth’s surface.

The after-effects of these reactions are the destruction of property, houses, and lands

How can scientists tell where the earthquake happened?

 It is crucial that scientists and other departments are aware of the oncoming of earthquakes so that they can work with governments and citizens.

Seismograms come in handy for locating earthquakes too and being able to see the P wave and the S wave is important.

P waves are also faster than S waves, and this fact is what allows us to tell where an earthquake was. 

The two waves have an important distinction. P waves travel fastest and are the first to arrive from the earthquake.

In S or shear waves, rock oscillates perpendicular to the direction of wave propagation.

However, they also have a commonality. Both P and S waves travel outward from an earthquake focus inside the earth.
 

It is important for us to understand earthquakes so that we can vary them. We should also be aware of some safety procedures to avoid them, as they can occur anytime. 

As responsible citizens and the future of the world, we should be aware of these facts.