An epicenter is the point on the earth's surface directly above where the earth begins to fracture in an earthquake. The focus lies beneath the epicenter. The epicenter is located from records of earthquake waves created by a seismograph.
Damage at the epicenter of a quake depends upon the size and depth of the fracture at the focus. Shallow quakes are most common, accounting for 75 percent of the energy produced by earthquakes each year. Earthquakes occurring more than 180 miles below the earth's surface occur in island arcs or deep ocean trenches. They are created by subduction of a tectonic plate.