Weather Insider: Why do we sometimes see earthquake magnitures change after the fact?

California is the most seismically active state in the country. We know that very well here in Southern California. The reason why we have so many earthquakes is because of the countless fault lines running through the state. There are hundreds running through or around the Coachella Valley alone.

Sometimes, an earthquake will be registered at an initial intensity. However, as we get more information from other sources, scientists are then able to go back and decipher what the true magnitude of the earthquake was. Dr. Kate Scharer from the USGS compared it to when you hear something fall in your house, but you're not exactly sure what fell or where until you go and check it out for yourself.