Did you know that Milwaukee feels the occasional earthquake? It's true, in fact the last tremor that Milwaukee felt was on June 28, 2004, and the epicenter was in northern Illinois. There have been at least 20 different occasions where tremors have been felt in Milwaukee in the last 140 years.
So even though Milwaukee lies within one of the zones of least hazard for earthquakes, it still gets the occasional tremor. For more information on earthquakes in the United States and the world, check out the U.S. Geological Survey's Earthquake Center web site.