Explain the difference between a focus and an epicenter?

Question

Explain the difference between a focus and an epicenter?

Answer 1

The term focus is somewhat vague but it usually refers to the hypocenter of an earthquake. A hypocenter (focus) is the center point of an earthquake in 3 dimensions x,y,depth.

The epicenter is the surface point directly above the hypocenter where the earthquake was centered. If you were to plot an earthquake on a map you would be looking at the epicenter location.

Answer 2

The actual three-dimensional location where an earthquake rupture starts is the focus (also called hypocenter).  The place on the surface of the ground above the focus is called the epicenter.  So the epicenter you could plot on a map, but the focus would be below ground level so you'd need a cross-section of the earth to see it.