Missouri - A small earthquake rattled the St. Louis region early Tuesday, shaking some people awake but not causing any reported damage.

The quake, which hit at 3:10 a.m. Tuesday, was a magnitude 3.9 temblor, according to scientists examining data at the U.S. Geological Survey in Golden, Colo.

"A lot of people felt it, but we're not talking about damage," said Don Blakeman, a geophysicist with the U.S. Geological Survey. "It was pretty short duration."

The city closest to the epicenter was Richwoods, six miles northeast of the quake center.

About 2,600 people logged on to the Geological Survey's website to report having felt the quake. Several hundred people from the St. Louis area's ZIP codes reported the quake as having the intensity of subtle shaking.

The shaking lasted several seconds. Some said three or five seconds; others claimed it lasted about 30 seconds, although Blakeman said the fear a quake produces likely caused those people to exaggerate.

Mary Morgan, 52, of Bonne Terre, said she woke up to the shaking.

"If that was an earthquake, do I dare go back to sleep?" she said. "It was a constant rumbling."

In some areas, such as in Potosi, residents reported a more intense shaking. It was felt indoors by many people who reported dishes, windows and doors rattling, and the walls making a cracking sound.

Brad Barton, director of the Washington County 911 service, said police dispatchers got calls from about 30 people right after the earthquake.

"A few thought it was an explosion," Barton said.

Barton drove around the county near the epicenter to look for damage but found nothing amiss, he said.

A handful of reports came in from people in the Illinois communities of Belleville, Red Bud, Granite City and Caseyville who said they felt it. A few people as far away as Kentucky, Ohio and Alabama also reported feeling the swaying from the earthquake, according to the U.S. Geological Survey's earthquake hazards program.

It apparently occurred in what's called the Ozark dome region, outside the New Madrid zone.

Blakeman said the earthquake was shallow, at least by earthquake standards, at 3 miles deep. He said it's unclear which fault it was on; he added that authorities might never be able to pinpoint which fault.