Earthquakes mainly happen on or near to plate boundaries.
As the plates slide under, over or past each other, friction causes the plates to lock together.
As the pressure increases, weaknesses or fault lines in the earth's crust close to the boundaries begin to fail.
The fault line breaks and the stored energy is released and travels outwards from the focus as seismic waves.
The epicentre of the earthquake is on the earth's surface directly above the focus and is likely to suffer the greatest amount of damage.
The closer the focus is to the crust the greater the damage.
The earthquake's energy is recorded by a seismometer, which measures the energy released by the earthquake using the Richter scale (1-10).
The Mercalli scale (I-XII) is a scale used to measure the damage caused by an earthquake.
Primary effects happen immediately; they include the destruction of buildings, breaking glass and falling masonry.
Secondary effects occur hours or days later; these include tsunamis, disease from contaminated water, loss of communications, fire and a damaged economy.Â