When an earthquake occurs, the body waves travel through the interior, but it is at the surface where they are “felt” as a disaster. The epicenter is the primary contact point between the internal energy release and human civilization. It is here that the P-waves arrive first, followed by S-waves and finally the destructive Surface waves. The epicenter serves as the starting point for mapping “isoseismal lines” (lines of equal intensity). Even though the focus is the real origin, the epicenter is the geographic marker used for emergency response and for identifying the proximity of the quake to populated cities.