I am in central Missouri so did not feel the M5.4 earthquake in east Illinois. The link is to the tectonic summary, which is interesting.
"In addition, geologists have found evidence of eight or more prehistoric earthquakes over the last 25,000 years that were much larger than any observed historically in the region. "
See the map for the "Illinois basin-Ozark Dome" region. The last couple of earthquakes larger than M2.5 in Missouri, including a M2.8 a couple of weeks ago, were west of the New Madrid zone proper..just west of the flat area of the Mississippi embayment. They were within area of Ozark dome as outlined in the link. Hmm, anyone want to find a link to the reference of the 8 or more larger quakes? We may have to reconsider not having earthquake insurance.
I'll email a geologist/seismologist L. Seeber who works (somethime with S. Hough) on intraplate earthquakes in eastern US and elsewhere and see if he has any comment and get permission to post that comment here. There are a couple people at the university here who also work on the region. I was planning on working at home and going out and buying some azaleas to plant this weekend, but maybe I better head in this PM.

The quake was strike-slip. It was consistent with ENE-WSW shortening (strain). The eastern USA is under ENE-WSW maximum principle stress (stress). Guess theer are some people in Illinois and Indiana who are feeling a little stress now.

I wonder if the high water levels have had any effect? I wonder if the water levels have been high there now or in the last few weeks. The depth of earthquake on the USGS page is 11.6 km "set by location program". Might be interesting to see the actual depth later.
Chris.

• Illinois earthquake history