epicentre

An epicenter, or epicentre in British English, is the point on the Earth's surface directly above the hypocenter (focus) of an earthquake—the location where rupture initiates underground. The hypocenter lies at a depth below the surface, while the epicenter is the surface projection of that point. For many earthquakes the epicenter is near the area of strongest shaking, though local geology and depth influence intensity at the surface.

Seismologists determine epicenters by analyzing arrival times of seismic waves recorded at multiple stations. P-waves travel fastest, followed by S-waves. The difference in arrival times gives a radial distance from each station to the epicenter. The intersections of these distance circles from at least three stations locate the epicenter; more stations improve accuracy. Modern methods use triangulation, waveform inversion, and data from global networks, sometimes incorporating GPS and aftershock patterns.

The epicenter is given by geographic coordinates on the Earth's surface. The term epicentral distance denotes the surface distance from the epicenter to a location. The term does not indicate fault length or rupture extent; those relate to the hypocenter and the fault geometry. Many earthquakes have some uncertainty in the epicenter due to limited station coverage or complex rupture.

The variant spelling epicentre is used in British English and many Commonwealth countries; epicenter is the standard American spelling. The concept is widely used in seismology, emergency planning, and scientific reporting.