How do earthquakes happen?

Earthquakes are caused when rock underground suddenly breaks along a fault. This sudden release of energy causes seismic waves that make the ground shake. When two plates are rubbing against each other, they stick a little. They don't slide smoothly making the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates start moving and continue to move until they get stuck again.