Early-morning temblor centered Downstate felt nationwide

5.2 MAGNITUDE | JOLTED A-QUAKE

A pre-dawn earthquake -- officially labeled as "moderate'' --mostly damaged work and school productivity Friday as Chicagoans swapped stories about windows rattling and beds rumbling.

Still, Chicago building inspectors fanned out across the city Friday to check buildings, bridges and transportation lines after the earthquake, which could be felt as far away as Atlanta.

» Click to enlarge image

City officials were asking companies to check buildings and construction areas to make sure there's no damage from an early morning earthquake that rocked the Midwest; (inset) Mike Dunkel, 57, owner of the Wagon Wheel Discount Liquor cleans up damaged stock in his Mt. Carmel, Ill., liquor store.
(AP)

Facts about Friday's earthquake

* The 5.2-magnitude temblor occurred at 4:37 a.m. and was centered 6 miles southwest of Downstate West Salem and 66 miles west of Evansville, Ind.

* It was felt as far away as Atlanta and Michigan.

* The temblor was one of the strongest ever recorded in Illinois. The strongest was in 1968, when a 5.3-magnitude temblor was centered near Dale in Hamilton County, about 75 miles southeast of St. Louis.

Source: U.S. Geological Survey

No damage was reported, city officials said after checking "key locations" that included skyscrapers, the Navy Pier ferris wheel and construction cranes.

The quake, which began around 4:37 a.m., registered 5.2 at its epicenter 230 miles south of Chicago. (By comparison, the quake that hit the California Bay Area during the 1989 World Series registered 6.9.)

No serious injuries were reported, but the quake could be felt as far west as Kansas, as far north as Upper Michigan, and as far south as Georgia, said the U.S. Geological Survey.

Friday's quake was centered near Downstate West Salem and lasted a matter of seconds. About five hours later, aftershocks that registered as high as 4.5 rumbled through the region. Officials said more aftershocks may be felt in the next few days.

"Earthquakes in the central U.S. are infrequent, but not unexpected,'' said Harley Benz, seismologist for the Geological Survey.

Earthquakes occur when two blocks of the Earth suddenly slip past one another. There are 500,000 detectable earthquakes globally each year, but only 100,000 of those can be felt and only 100 cause damage, the Geological Survey said.

City operators handled more than 300 calls from alarmed residents, said Jim Argiropoulos, acting executive director of the Office of Emergency Management and Communications.

Not all Chicago buildings are built to withstand earthquakes, but modern skyscrapers "typically have some small movement built into their design,'' said city Building Commissioner Richard Rodriguez.

None of Exelon Nuclear's six Illinois nuclear energy stations were affected by early-morning seismic activity, the company said.

The quake involved the Wabash fault, which some experts believe is a northern extension of the New Madrid fault that stretches into southern Illinois.

In 1811 and 1812, the New Madrid fault produced a series of earthquakes estimated at magnitude 7.0 or greater. They were centered in New Madrid, Mo., 140 miles southeast of St. Louis. Experts say that with today's much higher population in the Midwest, another major quake there could destroy buildings, bridges and roads, disrupt communications and isolate areas.

The last earthquake in the region to approach the severity of Friday's was a 5.0 magnitude quake in 2002. The strongest earthquake on record with an epicenter in Illinois was a 5.3-magnitude temblor that occurred in 1968.