Earthquakes are caused when rocks underground break. This sudden release of energy gives rise to seismic wave and make the ground shake. When two plates rub against each other they stick a little. The rocks still push against each other but are not moving. Gradually, the rocks break because of the building pressure. When rocks break, an earthquake occurs. During the earthquake and afterwards, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks are called the focus of the earthquake. The place right above the focus (on top of the ground) is called the epicentre of the earthquake.