Quake Watch

CHICAGO (CBS) ― A 3.8-magnitude earthquake hit early Wednesday in the far western suburbs.

The U.S. Geological Survey said the earthquake struck at 3:59 a.m. Its magnitude was originally estimated at 4.3, but the figure was later revised to 3.8.

The epicenter of the earthquake was 1 mile south-southeast of Pingree Grove, which is about 40 miles northwest of Chicago. The epicenter has also been revised; it was originally reported farther south in the Kane County town of Virgil.

Kane County sheriff's spokesman Lt. Pat Gengler says dispatchers have been flooded with calls from startled residents, though no injuries or damage have been reported.

Gengler says several residential and business alarms were triggered, but deputies hadn't been called for assistance.

National Earthquake Center geophysicist Randy Baldwin said as of 5 a.m., there had been no reports of any damage.

"I guess if there is damage, it would probably be light, or something based upon fallen objects or something like that," he said.

A quake this small wouldn't be expected to do severe damage, Baldwin said.

"It would have been felt by many people indoors, and it would have felt like a vibration due to a heavily-loaded passing truck or something like that," Baldwin said.

The earthquake was felt widely throughout the region, as far away as Iowa, Indiana, Michigan and Wisconsin, Baldwin said.

Residents reported being shaken out of bed and finding books and tools scattered across the floor after falling from shelves.

Viewers have been sending e-mails and Twitter postings by the dozen about the quake. They reported feeling the earthquake in Elgin, Bolingbrook, Naperville, and several other far west, northwest and southwest suburbs.

"I live 6 miles from Virgil. At 4 a.m. the house shook as well as the bed I was sleeping in," wrote Kathy Ghawi. "My husband and I searched the house and outside for the source of the shaking; we thought something hit the house -- a truck or airplane? Then we figured out it must have been an earthquake. Unbelievable. Snow fell off the roof."

"Out of nowhere, my house started to shake very hard for about 10 seconds then stopped, then went again for about 8-10 seconds… I didn't know what was going on," wrote viewer Nick Howson of Hoffman Estates. "I thought a snow plow might have crashed into my house."

Viewer Y. Dinwiddie of Batavia wrote: "It was so violent that a basket full of clothes that was sitting on our dryer was thrown to the floor, our sump pump was activated and our sons were awakened. We went all through the house, worried that perhaps a tree fell in the yard or something, but there had been no sounds except our bed creaking and things falling off shelves."

Rachel Olson was working at the 7-Eleven at 404 W. State St. in Sycamore when the quake happened.

"The windows and ceiling were rattling and one ceiling tile fell out," Olson said. She thought it lasted "about a minute, if that" and had not seen any emergency vehicles on the road as of 5:30 a.m.

"Most people thought [the earthquake] was a semi going by," she said.

Winnebago County Sheriff Sgt. Aaron Booker said when he heard the quake he thought it was thunder. "I felt the whole building shake," Booker said.

One viewer even reported feeling the earthquake in the city of Chicago.

"I live in a three story house in Hyde Park and I could feel the attic moving back and forth!" wrote Twitter user Kiratiana.

WBBM's Mary Kay Kleist also felt the earthquake at the WBBM Broadcast Center in the Loop, while she prepared morning's the weather forecasts.

"Just a minute before 4 o'clock this morning, I was in the studio, and suddenly, I thought a truck was going to hit the building, just like we heard in the interview," Kleist said, "but the lights started moving in the studio, and you could tell something happened."

This was the second earthquake to strike in Illinois in the past two years. On April 18, 2008, a 5.2 magnitude earthquake struck with an epicenter about 7 miles from downstate Mt. Carmel, about 230 miles south of Chicago.

That earthquake was felt around the state, including in Chicago. Downtown skyscrapers shook, but damage was mostly seen downstate.

The next most recent severe earthquake in the area hit in 1968. That earthquake had a magnitude of 5.3.

Those earthquakes were both centered on the New Madrid fault downstate. The area where the Wednesday morning earthquake struck is not nearly as active as the New Madrid fault, but it has seen other earthquake activity in recent years.

There was a 4.2-magnitude earthquake in the area in June 2004, and before that, a 3.0-magnitude earthquake in 1985, Baldwin said.

U.S. Geological Survey geophysicist Amy Vaughn said the cause of the earthquake will be hard to determine, since there is no clearly delineated fault line in the area.

The fault where the earthquake occurred is "potentially connected" to the Wabash fault zone, a northern extension of the New Madrid fault.

But, Vaughn said, "This is not a region where we expect to have this."

In 1811 and 1812, the New Madrid fault produced a series of earthquakes estimated at magnitude 7.0 or greater.

The Wabash fault zone generated a magnitude 5.0 quake in 2002 and a 5.1 in 1987.

In 1990, scientist Iben Browning said the New Madrid fault line was due for a catastrophic earthquake, but that never happened.

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