"We don't even have a single seismograph in the Wabash Valley zone," he said. "We haven't spent the money looking up there as in the New Madrid zone."

That means that the shock waves for that quake were measured using instruments 100 or more miles away, in places like St. Louis, New Madrid and Kentucky.

"We're missing how much amplification you're getting at the epicenter. It's not going to tell you how strong it was at the earth's surface," he said.

The 1968 quake, with its epicenter due west of Evansville, was about 35 miles from the Wabash River. It measured 5.4 on the Richter scale. In June 1987, a 5.0 magnitude quake was centered just north of today's earthquake.

Rogers said a 5.2 quake, which today's was, might cause shaking for 10 seconds and shouldn't cause a whole lot of damage.

Across many otherwise dark neighborhoods, lights went on as people climbed out of bed to check for damage. Dozens of houses in a Freeburg neighborhood lit up before the shaking stopped, and emergency phone numbers began ringing almost immediately, police said.

"Everyone's been calling," said a woman answering phones for the Freeburg police.

J. W. True, a security garage at The Lofts at Lafayette Square in St. Louis, was patrolling near an abandoned factory next to the apartments when he heard a sound in the metal vents above him.

"It rattled them real good," True said. "I was nine hours into my shift, and that really woke me up. I thought, 'Did I really feel that?"'

He started walking back to the apartments and one of the tenants shouted down from a 4th floor window and yelled, "Is that what I thought it was?"

Kusky said the quake originally had been recorded at 5.4 on the Richter scale by the U.S. Geological Survey, but it was downgraded to 5.2 by about 6 a.m. The force produced by a 5.4 are less than 10 times greater than a 5.2

Kusky said it's not unusual for the number to be revised.

"It's a complicated calculation and we have to take measurements from different seismic stations all around," he said. "It takes a little bit of time to average all the stations."

The earthquake should be a reminder to St. Louis residents, Kusky said, that we do live in an earthquake prone area. He suggested that residents consider acquiring earthquake insurance, recommends they not sleep with any large objects on the wall above them and keep life-sustaining supplies on hand. But not to worry, the huge earthquakes like the devastating series of quakes in 1811 and 1812 come just once every 400 or 500 years.

"We do live in an area that has earthquakes every once in a while," Kusky said. "We can have larger earthquake events and we should be prepared."