In earthquake science, the point on Earth’s surface directly above the underground focus is the epicenter.
The focus, also called the hypocenter, is where rupture begins inside Earth. The epicenter is found by projecting that location vertically upward to the surface. It is therefore a geographic point, not the place where the earthquake necessarily causes the greatest damage.
Seismologists locate an epicenter by comparing the arrival times of P waves and S waves at several seismic stations. Because P waves travel faster, the time difference indicates each station’s distance from the source. Circles drawn around multiple stations intersect near the epicenter.
The epicenter is often confused with the focus. The focus is underground, while the epicenter is on the surface. Strong shaking can occur far from the epicenter, depending on depth, distance, local geology, construction quality, and the direction of fault rupture.