Northern Illinois averages one earthquake every five years. Compare that to southern Illinois, near the New Madrid Fault, which is a lot more active, there is at least one earthquake a year. Even though Monday's night's quake lasted about 3 seconds, it will have a long lasting impression on scientists.
The earthquake just outside of McHenry may not have made an impact on the community-- at a magnitude of 2.4, it's considered minor -- but it means a big discovery for local geophysicists.
"We don't know much about the faults in northern Illinois because everything is covered by soil," said Northern Illinois University's Philip Carpenter. "We can't really see the bedrock. So whenever we have one of these earthquakes, it tells us there's a fault buried in that location."
Carpenter says earthquakes in this part of the state are not common and the challenge is to map out the actual fault line in the region.
"We have these sporadic small earthquakes like we experienced last night. They're sort of mysterious, but they're interesting at the same time," said Carpenter.
Carpenter studied the readout of Monday night's 3-second quake on the school's seismograph. He says, at the most, it felt like a snow plow rumbling down the street.
There have been a handful of quakes in the state in recent years that were stronger. This quake was only one-tenth of the strength of the earthquake east of Sycamore two years ago.
Still, it was enough to have residents near the epicenter talking.
"I thought it was very bizarre. I never thought there'd be an earthquake in Illinois," said resident Dawn Dages.
"My husband and I were watching television. All of a sudden, it was almost like a large truck must have come up to the house. As quickly as you felt the motion was as quickly as it went away, and it shook the whole home," said resident Karen Lewis.
The Illinois Emergency Management Agency is holding a drill next week to help residents know what to do before, during and after an earthquake. It is called the Great Central US Shakeout. It will take place next Tuesday, February 7, in several states.
