The Fault Might Not Be New Madrid's After All
The Wabash valley seismic zone may create the “big” Midwestern Quake
Seismologists predict that the Wabash Valley seismic Zone, which intersects and interacts with the New Madrid System will produce a devastating earthquake in Mid America.
The New Madrid Fault System is the better known of two major Midwestern fault systems. It extends south from Cairo, Illinois, and through Missouri, Arkansas, Mississippi, and parts of West Tennessee. The less famous Wabash Valley Seismic Zone, is centered in the Wabash River Valley, straddles the state line between southeastern Illinois and southwestern Indiana, and extends into part of Western Kentucky.
Seismologists believe that the Wabash Valley Fault runs through rocks from the Precambrian Era - 4,500 -542 million years ago - of the earth’s history and that the fault has always been active. Earthquakes have rocked this tectonic zone for the past 20,000 years and some have registered a 7.5 on the Richter magnitude 10 scale.
Famous New Madrid Zone Earthquakes The most famous series of earthquakes in the New Madrid Fault System occurred in 1811-1812. Dr. Michael Wysession associate professor of earth and planetary sciences at Washington University in St. Louis, believes that a recent re-analysis of data by United States Geologic Survey shows that the New Madrid fault risk is much less than was thought three decades ago. The three notable earthquakes that occurred at the end of 1811 and the beginning of 1812 were not magnitude 8s, rather magnitude 7s. A magnitude 8 is 30 times more energetic than a magnitude 7.
Another New Madrid Zone earthquake rocked Illinois on November 9, 1968, and measured 5.4 on the Richter scale. It affected 23 states over a 580,000 square mile area and caused much structural damage to buildings, but no fatalities. When they were researching the1968 Illinois earthquake, seismologists discovered the Cottage Grove Fault in the Southern Illinois Basin. The Cottage Grove fault is a small tear in the earth’s rock running west to east under Saline County, near Harrisburg, Illinois. It connects to the north-south running Wabash Valley Fault System at its eastern end.
Wabash Valley Zone Earthquakes The next Wabash Valley Seismic Zone earthquake rocked Indiana on June 18, 2002. It measured 5.0 on the Richter scale and struck near Evansville. According to the Indiana University Geological Survey, the earthquake warned the residents of the Wabash Valley Seismic Zone that earthquakes can, and do, strike in their own back or front yards.
Dr. Won-Young Kim, a seismologist at the Lamont-Doherty Earth Observatory at Columbia University, investigated the probabilities of future earthquakes in the Wabash Valley Seismic Zone. He discovered that an ancient fault line from the Precambrian era – 4.6 billion to 570 million years ago - has reactivated and probably caused the 2002 earthquake. According to Won-Young Kim, “This area was once as seismically active as the Gulf of California is today. The reactivation of this fault may be due to the forces that are moving the North American Plate over the Earth’s mantle. The depth of this earthquake suggests that these forces are quite large, even though they are far away from present plate boundaries.”
On April 18, 2008, the 102nd anniversary of the 1906 San Francisco earthquake, a magnitude 5.2 earthquake along the Wabash Valley Seismic Zone struck near the community of West Salem, Illinois. It jolted communities across southern Illinois, southern Indiana, western and central Kentucky and eastern Missouri. People in Chicago and St. Louis, 123 miles away, felt its vibrations.
The Wabash Fault May be Taking Over Douglas Wiens, also a professor of earth and planetary sciences at Washington University in St. Louis, speculates that the New Madrid Fault may be inactive and the Wabash Fault is taking its place. He says "the strongest earthquakes in the last few years have come from the Wabash Valley Fault, which needs more investigation."
Both Dr. Wiens and Dr. Wysession say that an earthquake in the Midwest is felt at greater distances than those in the Western United States because the earth's crust beneath the Midwest is ancient, stiff, and cold. They state the the rock is about 1.7 billion years old and the seismic waves travel long distances through this type of crust, mkaing an earthquake felt hundreds of miles away, even if it is a small earthquake. The rock is hotter in the Western United States, which dampens the shock waves and they are not felt as far away.
Seismologists Predict 90 Percent Chance of Quake Before 2055 Many seismologists predict that a future earthquake in the Midwest is likely, forecasting a 90 percent chance of a 6-7.0 magnitude quake before 2055. They say it will very likely originate in the Wabash Valley Seismic Zone and much less likely in the New Madrid Zone.
The Mechanics of Earthquakes and Faulting, Christopher H. Scholz, Cambridge University Press, 2002.
An Introduction to Seismology, Earthquakes and Earth Structure, Seth Stein, Michael Wysession, Wiley, Blackwell, 2002.
Geodyanmics, Donald L. Turcotte, Cambridge University Press, 2001
"Fault-Plane Determination of the 18 April 2008 Mount Carmel, Illinois, Earthquake by Detecting and Relocating Aftershocks", H.F. Yang, L.P. Zhu, R.S. Chu, Bulletin of the Seismological Society of America, Volume 99, December 2009, Issue 6, pages 3413-3420.
"Evidence of Possible Induced Seismicity in the Wabash Valley Seismic Zone from Improved Micro Earthquake Locations", Kevin C, Eagar, Bulletin of the Seismological Society of America, Volume 96, Issue 5, October 2006. Pages 1718-1728.