Magnitude, according to the U.S. Geological Survey, “is a number that characterizes the relative size of an earthquake.” To calculate the size difference between a 7.0 and a 4.8, we’d take the difference in magnitude — 2.2 — and raise 10 to that power.

For more info, please read the original article by Japan Times:
https://www.adn.com/alaska-news/2018/12/07/size-vs-strength-comparing-earthquakes/