A fault line is a separation or crack in the Earth's crust. It is the line where two or more of the tectonic plates in the Earth's crust butt against each other. An earthquake occurs when these plates move against each other. The amount of force applied will determine how powerful the quake will be.

external image images?q=tbn:ANd9GcTrMJ5f6UUEhqE0IAh9Yfr88-G7HLeZJi68QXljrLN1ujXG3Ay2external image images?q=tbn:ANd9GcTrJi4If8jHdzpM9KqfHQ9LNRzBJVTu71SrXK38SHQBROF8bLJ7