A magnitude 4.1 earthquake shook north central Illinois early Monday morning as many residents slept.

The earthquake, originally reported at magnitude 4.5, had an epicenter about 35 miles south-southwest of DeKalb, about 3.1 miles underground.

The 1:11 a.m. earthquake was relatively minor, said Paul Stoddard, associate professor of geology and environmental geoscience.

“It’s a good size quake for northern Illinois, but it’s not unheard of,” Stoddard said.

Northern Illinois is not immune to earthquakes, Stoddard said, and sits atop at least two known inactive fault structures.

The tremor was felt from Wisconsin to Missouri and from Michigan to Iowa, according to the U.S. Geological Survey.

The last one felt in the DeKalb area was in 1999 and registered at magnitude 3.5.

Georgianna Henry, a math instructor at NIU, said she was asleep in DeKalb when Monday’s three-second earthquake hit. She said she did not notice it.

“I did wake up around that time, so maybe I did [feel it],” Henry said. “I was in an earthquake a few years ago in Buffalo [New York], and it felt like a child was jumping on the end of the bed.”

The shaking had little potential for damage, Stoddard said, and it does little but give people something to talk about.

DeKalb police were inundated with about 100 calls within a 15-20 -minute time-frame, but were not sure what had happened until 10 minutes after the earthquake when they received a call from NIU, Lt. Jim Kayes said.

In Shabbona, about 12 miles southwest of DeKalb, resident Steve Wilhelm did not feel any shaking as he slept.

Jim Bryant, director of architecture and engineering services, said he had received no reports of any damage on campus. He said with an earthquake of this size, the most you would see is some rattling.

His department would oversee inspections if some buildings may have been damaged, but no requests for inspection had been made, Bryant said.

Stoddard said there is probably not a lot to learn about an earthquake like this, especially since the funding is not there for a region with so few earthquakes.

If anything, it may help geologists better map the fault structures that are beneath glacial till in Illinois, Stoddard said.

Stoddard said the earthquake may be the bedrock rebounding from the weight that ice age glaciers placed on the continent until about 10,000 years ago.

The ice then was tens of meters thick and put significant weight on the land, and the crust is still adjusting itself, Stoddard said.

Stoddard said he was disappointed that he slept right through the quake.

“I always miss things like that,” he said.