Past exam of the physics of the Earth as a Planet course of the University of Cambridge / 2014 / Paper 1 / 1 / a

The hypocentre is the point where rupture begins. The epicentre is its projection onto the Earth's surface. An earthquake centroid is an effective spatial average of moment release over the rupture, with a corresponding mean release time. Initiation and average release need not occur at the same place or time, especially for an extended, asymmetric rupture.