The entire surface of the earth is made up of several wide, thin and rigid plate like blocks. These are in constant motion with respect to each other. This causes most earthquakes at edges of plates and a few earthquakes within the plate. The movement is very slow but in some places it is as much as about 5 cm per year. Earthquakes occur almost everywhere in the world.
Some regions have more earthquakes than other parts of the globe.
Earthquakes can be caused by other reasons too. Volcanic activity can shake the ground. Blasting, quarrying and mining can cause small earthquakes. Underground nuclear explosions are also man made earthquakes. Tremendous amount of energy is released during an earthquake.