There are at least two active seismic zones in the US Midwest. Small tremors and quakes are not unknown or all that unusual, altho IME they're not something we expect with the same level of awareness as folks along the San Andreas fault, for instance. There have been 3-4 that I remember feeling here in SW Ohio in the past 25 years or so.
More serious seismic activity is a possibility in the case of both, there is at least some geological evidence that it's happened with the Wabash Valley zone. For the New Madrid zone, there was a well documented series of 7+ magnitude quakes in the early 1800s, one of which was strong enough to cause a wave in the Mississippi that flowed upstream and to create geological shifts that left waterfalls and lakes where there weren't any before.