the area immediately above the origin of an earthquake

center of activity

a meeting-point of rays of light, heat etc; a point, distance, where the sharpest outline is given (to the eye, through a telescope, through a lens on a camera etc)

center of attraction

the central part of a church where the people sit

middle point

a central pin or point on which something turns; something on which an argument or discussion depends

center point about which something

an apparatus for operating several telephone connections, e.g. in an office

center of activity