It's not rare to have an earthquake in the Missouri, Illinois, indiana, area as far as geologic time goes. Back in 1812, The New Madrid fault line shifted and set off a 8.0 or better earthquqke. It even changed the course of the Mississippi to flow north for a while.

Check it out.

http://en.wikipedia.org/wiki/New_Madrid_Earthquake

My wife said some of her students felt it here in NW Ohio this morning about 6:30 am.