Earthquakes are caused when rocks underground suddenly break along a fault, releasing stored energy and causing the ground to shake. When two blocks of rock or tectonic plates rub against each other, pressure builds until the rocks break. This triggers an earthquake. During an earthquake and afterward, the broken plates or rocks will start moving again until getting stuck and pressure begins building once more. The spot where the rock breaks is called the earthquake's focus, and the area above the focus is the epicenter.