Explain how plate tectonics form faults and how faults cause earthquakes.

A fault is formed in the Earth’s crust as a brittle response to stress. Generally, the movement of the tectonic plates provides stress, and rocks at the surface break in response to this. If you whack a hand-sample sized piece of rock with a hammer, the cracks and breakages you make are faults. An earthquake is caused by a sudden slip on a fault, much like what happens when you snap your fingers. Stresses in the Earth’s outer layer push the sides of the fault together. The friction across the surface of the fault holds the rocks together so they do not slip immediately when pushed sideways.