Friday, April 18, 2008

5.2 earthquake rocks large region of Midwest

Residents across the Midwest were awakened Friday by a 5.2 magnitude earthquake that rattled skyscrapers in Chicago's Loop and homes in Cincinnati but appeared to cause no major injuries or damage.

The quake just before 4:37 a.m. was centered six miles from West Salem, Ill., and 45 miles from Evansville, Ind. It was felt in such distant cities as Milwaukee, Des Moines, Iowa, and Atlanta, nearly 400 miles to the southeast.

The quake struck at a shallow depth of 7.2 miles, according to the USGS. The agency initially said the quake had a magnitude of 5.4 but later verified it at 5.2.

A fault zone in the area where the temblor was centered has produced quakes in the past. Experts have said soil conditions in the central United States are such that shocks in the region tend to travel farther and be felt in wider areas than in places such as California where a 5.2 magnitude quake would be more quickly absorbed.

The quake is believed to have involved the Wabash fault, a northern extension of the New Madrid fault about six miles north of Mount Carmel, Ill., said United States Geological Survey geophysicist Randy Baldwin.

The last earthquake in the region to approach the severity of Friday's temblor was a 5.0 magnitude quake that shook a nearby area in 2002

In Louisville, Ky., the quake caused some bricks to fall off a building near downtown. Television video showed them strewn in the street.

In Chicago, officials were checking structures downtown to ensure there was no damage. The quake also shook skyscrapers in downtown Indianapolis, about 160 miles northeast of the epicenter.

The strongest earthquake on record with an epicenter in Illinois occurred in 1968, when a 5.3-magnitude temblor was recorded about 75 miles southeast of St. Louis, according the USGS. The damage was minor but widespread and there were no serious injuries.

In 1811 and 1812, the New Madrid fault produced a series of earthquakes estimated at magnitude 7.0 or greater said to be felt as far away as Boston. They were centered in the Missouri town of New Madrid (pronounced MAD rid), 140 miles southeast of St. Louis.

Experts say that with the much higher population in the Midwest, another major quake along the New Madrid fault zone could destroy buildings, bridges, roads and other infrastructure, disrupt communications and isolate areas.

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