My understanding is an epicenter is a position above the center of something, and that the term comes from seismology. Since the actual point at which an earthquake occurs is underground, when people refer to an earthquake being in San Bernardino, they actually mean the earthquake happened deep underground and the nearest point on the surface of the earth, the epicenter, is located in San Bernardino.
Recently, new reports from respected sources have called Wuhan, or Lombardi, or New York City, as the epicenters of the coronavirus outbreak. And Merriam & Webster gives "center" as the second meaning of epicenter.
When did the meaning of epicenter (from Greek for upon the center) expand to just mean the center of something important or substantial?