Why Was There Just a Weird Earthquake in the Middle of Illinois?

It happened almost without anyone noticing, but there was a weird earthquake Wednesday night right in the heart of Illinois. Why?

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Spoiler alert that I can't answer the "why" question at this point. All I know is that the USGS reported a 2.6 earthquake Wednesday night at 10:36pm south of Springfield, Illinois right in the middle of the state.

Other than the nearby well-known New Madrid Fault in the bootheel of Missouri, I'm only aware of a couple of earthquake faults in Illinois. There's a minor fault in northern Illinois known as the Sandwich Fault. The more dangerous area is the Wabash Valley Fault System which caused a relatively large 5.4 earthquake back in 1968. If I had to guess, I'd pin this strange shaker on that one.

Thanks to Gary Auerswald who sent me a note about a 5.2 magnitude quake in Illinois on April 18, 2008. The USGS said that during that event there "were at least six felt aftershocks greater than magnitude 3 and 20 aftershocks with magnitudes greater than 2 located by regional and national seismic networks".

There's an interesting theory shared on Wikipedia that the New Madrid Fault could become less active and that energy would transfer to the Wabash Valley Fault System. Yikes. That's one reason why the state of Illinois also warns citizens to prepare for the possibility of a major quake even though it's not extremely likely to happen.

Now we wait to see if the late night Wednesday night Illinois quake, which was only felt by 1 person apparently, is an isolated event or a precursor to something larger. Let's hope it's that first option.