The focus of an earthquake is a point at some depth in the earth from where radiation of seismic waves starts. Earthquakes are caused by the strain in the earth’s crust which in turn is a result of a number of factors. The point directly above the focus on the surface is called epicentre. The waves are felt most strongly at the epicentre, becoming less strong as they travel further away. The most severe damage caused by an earthquake will happen close to the epicentre.
At the epicentre, the strongest shaking occurs during an earthquake. Sometimes the ground surface breaks along the fault. Sometimes the movement is deep underground and the surface does not break.