Hypocenter

The hypocenter or hypocentreor (literally: 'below the center' from the Greek υπόκεντρον), also known as the focus, is the point inside the Earth where an earthquake originates. It is directly below the epicenter at a depth known as the focal depth.

The term hypocenter also refers to the point on the surface of the earth directly below the air burst of a nuclear detonation. In this context, the term "ground zero" is synonymous with hypocenter.