News Release 211

GEOLOGISTS EVALUATE
PREDAWN EARTHQUAKE CENTERED IN ILLINOIS

Volume 36-211

Contact: Hylan Beydler

(For immediate release)

573-368-2118

ROLLA, MO, APRIL 18, 2008 -- Missourians experienced the shocks of 5.2 and 4.5 earthquakes in Mount Carmel, Illinois, along the Wabash Valley Seismic Zone. Mount Carmel is approximately 130 miles east of St. Louis. The Wabash Valley Seismic Zone is located in southeastern Illinois and southwestern Indiana.

This morning's sizable temblor was felt from Georgia to Michigan and westward into Kansas.  Several aftershocks have occurred with reports of only minor damage.  Coincidentally, the Great San Francisco Earthquake measuring greater than 7.7 struck on this date in 1906.

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.  The largest recorded earthquake on the Wabash Valley Fault System was in 1968, which registered magnitude 5.4.  On June 18, 2002, a 5.0 magnitude earthquake struck the Evansville, Indiana, area.

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 (the size range of the 1989 San Francisco, the 1994 Los Angeles and the 1995 Kobe, Japan, earthquakes). Overhoff said, "A similar size earthquake occurring along the zone in this century has the potential to significantly impact not only Missouri but also residents in Arkansas, Illinois, Kentucky, Tennessee and Mississippi."  Beyond the damage from shaking, Overhoff explained, "If a big enough earthquake hits, the ground in some areas will actually liquefy.  When you have loose soil mixed with water, the ground loses its bearing strength and is susceptible to greater devastating effects."  The Department  of Natural Resources has a plan in place to implement a clearinghouse for the scientific community, should a significant earthquake occur in Missouri.

Overhoff and other earthquake experts from around the nation will convene next week in Seattle for the National Earthquake Conference to discuss the latest research on earthquakes and the generation of tsunamis.  Forty of the 50 states have some risk of earthquake.

For more information about earthquakes www.dnr.mo.gov/geology/.  For news releases on the Web, visit www.dnr.mo.gov/newsrel. A complete listing of the department's upcoming meetings, hearings and events, is online at www.dnr.mo.gov/calendar/search.do.

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Editor:  Photo is available at http://www.dnr.mo.gov/newsrel/NMmap6flat.jpg.

Caption:  This map of the New Madrid and Wabash Valley seismic zones shows earthquakes as circles. Red circles indicate earthquakes that occurred from 1974 to 2002 with magnitudes larger than 2.5 located using modern instruments (University of Memphis). Green circles denote earthquakes that occurred prior to 1974 (USGS Professional Paper 1527). Larger earthquakes are represented by larger circles.  Map courtesy of U.S. Geological Survey.