With the New Madrid fault just a hundred miles south of St. Louis, it’s long been known that the region is at a greater risk for an earthquake than other parts of the Midwest. But new research indicates that St. Louis is part of an area that has seismic activity of its own.
Geologists have identified a new seismic zone stretching from St. Louis to Cape Girardeau along the Mississippi River called the Ste. Genevieve Seismic Zone. Their research indicates that the zone is capable of producing moderate earthquakes every few decades and has the potential to produce a major earthquake every 2,000 to 4,000 years.
“It’s a roll of the dice, right. If you’re unlucky, it could happen in your lifetime. The odds are not high,” Indiana University Geologist Gary Pavlis said.
A moderate earthquake measures about a magnitude 5 on the Richter scale. Pavlis said they can be felt but would only dislodge a few bricks here and there.
He was part of the team of geologists from Indiana University, Purdue University, Illinois University, the Indiana Geological Survey and the Illinois Geological Survey who conducted the study. The team is called OIINK after the region they are studying--the Ozarks, Illinois, Indiana, and Kentucky.
The research team confirmed the seismic activity by densely populating the region with seismographs for a year in order to gather data about low magnitude quakes.
For comparison, the New Madrid Seismic Zone is twice as likely to produce a major earthquake as the newly identified Ste. Genevieve Seismic Zone. The New Madrid Seismic Zone stretches from southern Illinois, across the Missouri bootheel and into northeastern Arkansas.
In 1811 and 1812 the New Madrid fault produced a series of major quakes that measured above a magnitude 7 on the Richter scale. Those earthquakes were felt for hundreds of miles, and produced massive waves on the Mississippi River.
Because eastern Missouri and southern Illinois already have an elevated earthquake risk due to New Madrid, Pavlis said the Ste. Genevieve Seismic Zone is unlikely to impact insurance rates.
“This adds another layer, but in the grand scheme of the way they do hazard maps, it doesn’t really change things very much,” he explained.
Follow Camille Phillips on Twitter: @cmpcamille.