What is the focus of an earthquake?

The focus of an earthquake, often referred to as the hypocenter, is indeed the point beneath the Earth's surface where the rocks initially fracture and begin to move as a result of the accumulated stress. This point serves as the source of the seismic waves that propagate outward from the focus and cause the shaking felt during an earthquake.

Understanding the focus is essential in seismology because it helps scientists determine the extent and magnitude of the seismic activity. The focus is typically located at varying depths depending on the type of fault and the geological conditions, which in turn can influence the characteristics of the earthquake's impact on the surface.

The concept is distinct from other related terms such as the epicenter, which describes the point directly above the focus on the Earth’s surface, and seismic waves, which are the energy waves that travel away from the focus. By identifying the focus, geologists can better assess earthquake risk and understand the mechanics behind fault movements.