Earthquakes are vibrations or tremors in the earth's crust that are cause by the sudden release of energy along a fault line.

The seismic waves or tremors are known as shocks. The largest shock is called the main shock, the shocks before, the foreshocks, and the shocks after the aftershocks.

Shock waves or tremors travel out from the origin or focus of the earthquake. The site directly above the focus, on the surface, is known as the epicentre. Most damage is done here.

As the plates settle back to their normal positions after the earthquake (elastic rebound) more earthquakes, or aftershocks, can occur. These can do more damage to already weakened buildings and send panic through affected populations.