Earth's crust is broken up into irregular pieces called tectonic plates. These large pieces of crust were formed by the combination of gravity and rising heat from Earth's core. There are seven major plates and many smaller ones, all moving in relation to each other. The lithosphere refers to the crust and upper mantle that make up these plates.
As tectonic plates move past each other along fault zones, they sometimes get stuck. Pressure builds, and when the plates finally give and slip, energy is released as seismic waves, causing the ground to shake. This is an earthquake.
