DID YOU KNOW? An earthquake is the shaking that results from movement under Earth's surface. Earthquakes are caused by forces of plate movement, and they occur most commonly at transform plate boundaries. At transform plate boundaries, plates slide past each other in opposite directions. As the plates try to slide past each other, stress builds, especially along faults. If you recall, faults are cracks on Earth's surface that appear between plates. Excess stress causes rocks to break, which makes the plates release and move past each other with an abrupt movement. As a result, an earthquake begins.