This was actually not the first reminder that Yellowstone has issued forth from her bowels. In fact, one occurred 15 minutes earlier, but I was dead to the world. Actually, the past three days have held several earthquakes over 3.0 magnitude. The one that awoke me was the largest, with a magnitude of 3.8. Click here to see more!
These clusters of earthquake activity are considered entirely normal for Yellowstone. It is to be expected, since it is a volcano.
(Borrowed from: http://www.seis.utah.edu/req2webdir/recenteqs/Maps/Yellowstone.html)