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3/10/2010 1:01:00 PM Illinois shakes, rattles but does not roll
Do you need quake insurance?
While the earthquake Feb. 10 in northern Illinois did little more than wake people from their sleep, the Illinois Department of Insurance advised consumers to review their policies for earthquake coverage.
Dick Martuzzo, an insurance agent at Duncan Insurance in La Salle, said interest in earthquake insurance picks up after a quake. Earthquake coverage is generally separate from regular homeowners insurance and requires buying additional policies, usually involving high deductibles.
"In this area, to be honest, you would have to suffer a pretty big earthquake to have the coverage kick in," said Karen Grotti, insurance agent with Hummer Insurance in La Salle.
While earthquake insurance may only be effective after a catastrophic loss, Grotti said, this hasn't kept some Illinois Valley homeowners from buying coverage over the years.
"Some people want coverage for everything and they'll buy it," Grotti said.
On Feb. 10 a minor quake centered 60 miles northeast of La Salle caused no damage or injury but was felt by residents here.
"It's not unusual that we've had one up there," said Bob Bauer, engineering geologist with the Illinois State Geological Survey. The Chicago metro area has seen eight earthquakes going back to 1804, Bauer said.
Scientists generally accept that earthquakes could occur in the future as frequently as in the recent past.
"Geology is based on what has happened in the past," Bauer said. But he added: "We've been in this area for a very short time period for human observations."
There is an average of one earthquake per year in Illinois, according to the state survey. Minor-damage earthquakes hit about once every 20 years. Quakes causing serious damage happen every 70 to 90 years. Devastating earthquakes occur in the central U.S. about once every 700 to 1,200 years.
In the past week there were 989 earthquakes in the United States, according to the U.S. Geological Survey. One hit the New Madrid seismic zone that extends into southern Illinois.
The earthquake of Feb. 10 was not caused by that. It resulted from slippage in solid granite about a mile below the surface, Bauer said.
"We don't really have a picture of the fault," he said.
Fault lines mapped in the state have little to do with observed earthquakes, Bauer said.
A 1999 earthquake near Dixon had no connection to the nearby Sandwich fault zone or any other known faults in Illinois, the state survey said.
Further, the survey said there has been no measurable movement on any faults in northern Illinois since at least the beginning of the last Ice Age about 1 million years ago.
Terry McCleary, a geotechnical engineer in Tonica, said designing and building structures in northern Illinois is not bound by fault lines and earthquakes.
"The likelihood that we have an earthquake large enough that's going to cause damage isn't very likely," he said. "The closer we get to southern Illinois, it's much more prevalent, the designs are much more elaborate down there for the liquefaction of sand."
That means sand behaving like liquid. New Madrid quakes can make waterlogged sand flow to the surface.
The New Madrid earthquake of 1812 "rang church bells in Boston," McCleary said. "They even felt it up in Canada."
The 1812 quake lifted up the Mississippi River, temporarily halting its flow, Bauer said.
There are 100 to 200 earthquakes per year in the New Madrid zone.
"I grew up in southern Illinois and we would have earthquake drills," McCleary said.
New Madrid once lay on the edge of the continent, Bauer said.
"It was being pulled apart," Bauer said. "Now it's being squeezed in an east-west direction."
The seismology of northern Illinois is less clear. Finding clues requires seismic studies.
"There's a way to do it but it's really expensive," Bauer said. "We rely on private exploration of oil and gas."
The Midwest is safer because it lies in the middle of the vast North American plate. Movements here lack the energy found on the western edge of the plate.
"You're getting to the center of the mass of our plate, and it's more stable," Bauer said.
Predicting earthquakes is easier on the West Coast because faults are more active and well-defined.
"We can't do that here in the Midwest," Bauer said.
The most damaging earthquakes lie along plate boundaries, mountain chains and volcanoes. The largest recorded earthquake in the world was a magnitude 9.5 in Chile on May 22, 1960. The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska on March 28, 1964.
McCleary has experienced a few Illinois earthquakes. One a few years ago centered near Robinson was felt by McCleary in Matoon and by his wife in Tonica, he said.
Another quake in 1999 rolled him out of bed, he said.
McCleary said the Feb. 10 earthquake provided no such thrill.
"I didn't feel it at all and that kind of disappoints me," he said.