hypocenter

The point within the earth where an earthquake rupture begins — the actual origin of the seismic energy, typically miles below the surface. Also called the focus. The hypocenter is the place where the rock finally breaks after years, decades, or centuries of accumulating stress. It may be shallow (less than 40 miles deep, where the most destructive quakes occur) or deep (down to 450 miles, in subducting slabs of oceanic crust).