Residents of southeast Illinois were surprised early Thursday morning when the ground beneath them shook from a 5.2 earthquake centered 6 miles from West Salem, Illinois. Skyscrapers shook in Chicago and was felt as in Cincinnati and Milwaukee.
The quake occurred in the Illinois basin-Ozark dome region that covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis. Less active than the more famous New Madrid seismic zone, this region is subject to moderately damaging earthquakes every decade or two. Smaller earthquakes are recorded more often.
Image courtesy USGS