April 24, 2008

Earthquake More Than 100 Miles Away Awakens Many in Scotland County

Alarms clocks were replaced early Friday morning by quite a surprise for most area residents that were shaken awake by the rumblings of an earthquake centered more than 100 miles away.

“It woke Mark up, and he asked me “what was that?’” said Carla Myers. She looked at the clock and went back to sleep and likely wouldn’t have thought much about her husband being awakened without hearing the news about the earthquake the next morning.

That was the response for most folks in Scotland County. The vast majority slept right through the unusual event.

Later that morning, those that were awakened by the brief concussions that hit the area learned that a magnitude 5.2 earthquake centered near Bellmont, IL, had more than just woke people up early in southern Illinois and western Indiana at 4:32 a.m. when the natural disaster occurred.

But despite being the largest earthquake in the region since 2002, there were no major injuries or significant damage reported.

According to the United States Geological Survey, reports were received of minor structural damage in West Salem, Illinois and Louisville, Kentucky. The earthquake however was felt over a wide area of the Midwest, with the USGS receiving “felt” reports as far west as Kansas, as far north as the Upper Peninsula of Michigan and as far south as Georgia.

According to the Missouri Association of Insurance Agents reports of damage and shaking poured into the U.S. Geological Survey from areas across Missouri including numerous reports in St. Louis and towns along the eastern state border. By 11:00 a.m., nearly 25,000 independent reports had been recorded.

The Missouri Department of Transportation sprang to action with bridge inspectors mobilized in force, examining all state bridges in the eastern part of the state that may have been affected.

MoDOT officials indicated inspectors reviewed about 2,500 bridges located in the eastern third of the state and no damage was discovered.

“Our top priority today is making sure all our bridges are safe,” said State Bridge Maintenance Engineer Scott Stotlemeyer. “We’ve got hundreds of people checking bridges today. If we find any damage we’ll deal with it right away, and we won’t hesitate to close a bridge.”

In all, four tremors were reported Friday morning. A pair of smaller magnitude aftershocks were reported at 5:03 and 5:15 a.m. Both registered a 2.5 magnitude. Then at 10:14 a.m. a 4.6 magnitude earthquake was reported northwest of the original activity, about four miles from Noble, IL.

All of the seismic activity was centered on the Wabash Seismic Zone. The USGS points out that this large region borders the much more seismically active New Madrid seismic zone on the north and west, affecting parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas, stretching from Indianapolis and St. Louis to Memphis.

The Friday tremor was the second strongest on record for the region. The largest occurred in 1968, registering a 5.3 magnitude. Quakes of this magnitude strike the region once every decade or two according to the USGS, with smaller events happening as often as once or twice a year.

Dave Overhoff, geo-hazards geologist with the Missouri Department of Natural Resources’ Division of Geology and Land Survey in Rolla said, “While the movement was along the Wabash Valley Fault System, this system is independent of the New Madrid Seismic Zone.” Scientists understand that the Wabash Valley Fault System runs perpendicular to the New Madrid Fault along the north end of the system.

Moderately damaging earthquakes occur on the Wabash Valley fault about once every decade or two. Smaller earthquakes are felt about once or twice a year, which is considerably less active than the New Madrid Seismic Zone.

Overhoff said that the New Madrid Seismic Zone is the country’s most active seismic zone east of the Rockies and produces more than 200 small earthquakes each year along the zone. Most are too weak to be noticed by the public; however, the Center for Earthquake Research and Information in Memphis, Tenn., registered a magnitude 3.4 earthquake on Oct. 18, 2006, near New Madrid.

The New Madrid Seismic Zone extends 120 miles southward from the area of Charleston, Missouri, and Cairo, Illinois, through New Madrid and Caruthersville, following Interstate 55 to Blytheville and southward to Marked Tree, Arkansas. The zone crosses five state lines and cuts across the Mississippi River in three places and the Ohio River in two places.

In 1811 and 1812, the New Madrid Seismic Zone produced a series of earthquakes estimated at magnitude 7.0 or greater. Several thousand smaller earthquakes followed through mid-March. Fifteen of these quakes were magnitude 6.5 to 8.

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