What causes an earthquake exactly?

Earthquake!!!!!! Just the mere thought of the word sends chills down the spine of the toughest, meanest, angriest individual. When they occur, the first thing I would think is, is it the end of the world? So what cause earthquakes? Can you say, "are you near a faultline"? Faultlines are what plates of rock meet like a crack in your pavement where one side is a little higher than the other. These plates of course cover the whole world. Some times they seperate, sometimes they press against each other till one over comes the other. So a earthquake is the shaking or breaking of rocks. One would think that the earth is also a living thing because it has never stopped moving, and is always changing. One thing to think about. Another thing, this happens due to force and one would wonder, what causes the force? Some scientists call it "elastic rebound" and are still studying it.