Hypocenter and Epicenter   The region of initiation of seismic energy within the Earth during an earthquake is the focus or hypocenter (Figure 2).  This is the initial region along which a new fault forms or an old fault ruptures.  From the focus, slip along the fault spreads quickly.  The position on the land surface immediately above the hypocenter is the epicenter (Figure 2).  As rupture along a fault initiates, waves of energy travel outward from the hypocenter in a spherical fashion.   These waves of energy are strongest nearest the hypocenter but gradually grow weaker further away from the site of initial rupture.