Small quake a boon for geologists

Updated 2/11/2010 7:12 AM

Wednesday's 3.8 magnitude earthquake near Pingree Grove will have little lasting impact on suburban residents, but scientists are looking to the quake for clues about seismic activity in the region.

The quake took geologists by surprise and revealed a new fault line in central Kane County.


"There were no warning signs about this quake coming," said Randy Baldwin of the U.S. Geological Survey. "It was right out of the blue."

While small, the quake was felt by thousands of people from eastern Iowa to Michigan, according to the geological survey.

Although experts said the wide area where the shock was felt is consistent with quakes east of the Rocky Mountains, it is rare for northern Illinois to experience an earthquake of this size.

According to geological records, northern Illinois has only seen three comparable events in the past 25 years:

• In 2004, there was a magnitude 4.2 earthquake in LaSalle County.

• In 1999, there was a magnitude 3.5 quake in Lee County.

• In 1985, there was a magnitude 3.0 quake centered in Lombard.

The lack of damage reported on Wednesday is typical for an earthquake of that size, experts said.

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"Probably the most you'll see is some things knocked off shelves," said Don Blakeman, a geophysicist with the National Earthquake Information Center.

Like most earthquakes in the continental United States, Wednesday's shock was shallow, centered an estimated three miles below the surface.

That's in contrast to some Pacific quakes that emanate from as much as 400 miles below the surface and similar to the shallow but much more powerful quake that devested Port-au-Prince last month.

"It's true of this earthquake as well," Blakeman said. "It's shallow in the crest. It's just that the earthquake was so much smaller."

In general, earthquakes are rare east of the Rockies, although the most active region, the New Madrid Fault Line, runs from the tip of southern Illinois to Arkansas.

Experts said Wednesday's quake was unrelated to the New Madrid activity but said the quake leaves many unanswered questions.

"We have a really great learning opportunity," Northern Illinois University geologist Phil Carpenter said. "It's a total surprise."