Earthquakes occur most often along the edges of oceanic and continental plates. Oceanic plates are the large pieces of the Earth's crust that are located beneath the oceans. Continental plates hold the Earth's large land masses.
Earthquakes occur when the Earth's plates move and rub against or bump into each other. Quakes occur most frequently along the edges of plates, but they are also common along faults, which can be far from the edge of a plate. Faults are cracks where smaller sections of the plate move against each other. Cracks may be defined as normal, reverse or strike-slip faults. One of the most well-known faults, the San Andreas Fault, is a strike-slip fault.