Illinois May Have Faced a Massive 7.5 Quake, Not New Madrid

There's a reason why many in Illinois think of the New Madrid Fault when they think about earthquakes, but the largest in the state's history may not have come from that seismically-active region. Geology says the Land of Lincoln may have been rocked by a 7.5 magnitude quake once, but not from the fault in the southwestern part of the state.

What is the largest earthquake in Illinois history?

I was under the impression that the largest non-New Madrid earthquake in Illinois was a 5.4 magnitude quake on April 8, 2004. That is true, but not if you travel back into prehistoric times. According to Wikipedia, a paper by Washington University said that there is evidence in the rocks that Illinois was once shaken by a monstrous 7.5 magnitude Wabash Valley Seismic Zone quake in prehistoric times. Another paper theorized that the Illinois Basin is the most structurally-complex region on the North American continent.

What is the most powerful earthquake the Wabash Valley Seismic Zone is capable of today?

The Illinois Emergency Management Agency estimates that Illinois could get rocked by up to a 7.0 magnitude quake today. While it's not necessarily likely, there have been an uptick of quakes on the eastern side of Illinois over the past few years. That's one reason why it's good to be quake aware in Illinois and not just because of the New Madrid Fault.