Shake, Rattle and Roll

Just after 12:30 last night, we had an earthquake.  It was a 5.8.  Five minutes later, we had the first aftershock, a 4.7.  Since then, we have had 15 more aftershocks, none as strong as the original.  The epicenter was near Lincoln, MT, about 90 miles from us.   The quake is considered to be a "moderate" one, and was not the least alarming to us, both of whom grew up in the SF bay area of California.