Earthquake... in Illinois?

So I went to bed last night expecting the weather front off to the west to be rumbling through last night with thunderstorms that might wake me up... what did wake me up?  Yes an EARTHQUAKE!  It went on for probably 30 seconds and I really did feel things shake, not like the earthquake when I was younger and got yelled at for kicking the table.  Apparently a 5.4 (preliminary report) magnitude quake hit somewhere in the south east part of Illinois near the Indiana border between Mt. Vernon, IL and Vincennes, IN.  You can see the details from the USGS here.