Dear Tom,
Is it true that one of the largest U.S. earthquakes occurred in Illinois? How often do they occur here?
J. Swidler, Deerfield
Dear J. Swidler,
The earthquakes that you are referring to are the trio of New Madrid earthquakes that occurred in 1811-12 along the New Madrid seismic zone that extends from northeast Arkansas to southern Illinois. These three quakes, with magnitudes estimated at greater than 8.0 on the Richter scale, devastated the settlement of New Madrid, Mo., and literally changed the course of the Mississippi River. According to the Illinois State Geological Survey, earthquakes occur in Illinois about once a year, but ones strong enough to cause damage occur only about once every 20 years. The last major Illinois quake was a 5.0 event that did minor damage in the southeast part of the state near Lawrenceville and Olney.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
