the fault line is where two pieces of crust have split. the point within the earths crust where they have split is called the focus. the sudden jolted movement at the focus causes seismic waves to radiate outwards. the point directly above the focus at the ground surface is called the epicentre. once the seismic waves reach the ground surface, shaking is felt with the most shaking occuring at the epicentre. further away from the epicentre the shaking is less violent.