When the tectonic plates that make up Earth's crust move past each other, they often bump or rub against each other. The earth, or ground, above the plates moves as well. This movement is call an earthquake. Sometimes the plates get stuck. The pressure increase as the two plates try to move past each other but cannot. They finally move with a sudden and powerful jerk. This can also cause an earthquake. During a small earthquake, the ground simply shakes a little, and people may not even notice. However, a strong movement can cause the ground to shake and roll violently. It can make building and bridges fall. It can also cause the ground to split open and form a large fault, or crack.