Earthquakes - Major Causes of Earthquakes. Focus, Epicentre and seismic waves

Introduction and Causes of Earthquakes

Earthquakes are sudden vibrations of the lithosphere.
Over 10 million earthquakes occur each year, but most of them are too mild to be felt.
They cause loss of lives and property.

Major Causes of Earthquakes

Most earthquakes are the result of plate movements.
When plates move, friction causes pressure to build up slowly in the plate and energy is stored.
When the pressure exceeds the strength of rock, the rock breaks.
This releases the stored energy and produces seismic waves.
These waves move out in all directions and cause the ground to shake, resulting in earthquakes.
Some earthquakes are caused by volcanic eruptions.

Focus, Epicentre and seismic waves

Some earthquakes are mild, some others are rather destructive.
The severity of an earthquake depends on the amount of energy that is released.
The point of origin of shock waves is usually at a certain depth in the earth’s crust, known as focus.
The epicentre is the point on the Earth’s surface vertically above the focus.
Shock waves that travel outwards from the epicentre at different speeds in all directions are called seismic waves.
These waves cause the ground to shake, resulting in earthquakes.