Earthquakes in Illinois?

The United States Geological Survey is reporting that it has recorded a magnitude 3.8 earthquake in northern Illinois (see also the NY Times article). This is not unheard of; earthquakes do sometimes occur east of the Rockies (my own mother has told me of a medium-sized earthquake that was felt in Northeast Ohio a few decades ago). Nevertheless, northern Illinois is well outside of any geological hotspots (the US Geological Survey maps it in Seismic Zone 0, the zone of lowest risk). And this is especially troubling given - as we noted earlier - scientists' fears that the Haiti quake forewarns increased seismic activity and the hundreds of small tremors that have been rocking Yellowstone National Park over the past few weeks.