Researcher Shows How Mississippi River Flow Is Linked To New Madrid Seismic Zone Earthquakes

FAYETTEVILLE, Ark. - A University of Arkansas researcher has linked shifts in the course of the Mississippi River and its tributaries to earthquakes and landscape changes in the New Madrid seismic zone, helping to more accurately date past earthquakes in the nation’s heartland.

Accurate dates help scientists determine a better earthquake history and thus help forecast the frequency of future seismic activity.

Margaret Guccione, associate professor of geosciences, will present her findings today (Monday, Nov. 13) at the Geological Society of America's annual meeting in Reno, Nev.

Guccione has examined several loops of the Mississippi River in the New Madrid seismic zone that have been abandoned by the river in the past 2,400 years. Flood sediment of the Mississippi River fills the abandoned channels, which have since become oxbow lakes, and blankets the surrounding floodplain.

When an earthquake uplifts or depresses the abandoned channel, the area that floods and the type of sediment that fills the channel can change. Even the direction of the flow of small streams can be permanently altered. Guccione took core samples from sediments in one of the ancient loops of the river and used radiocarbon techniques to date the organic matter found in sediments at different levels. Some of this sediment had rapidly accumulated because of the shift in drainage direction that dates to A.D. 1470. This date correlates with other geologic estimates for a large quake in the New Madrid Seismic Zone.

"This shows how the river can be used to date earthquakes and folding based on its response to seismic events," she said.

Researchers study the Reelfoot Scarp, a geologic fold near Tiptonville, Tenn, because the formation of this ridge is related to large earthquakes in the New Madrid Seismic Zone. Guccione has spent years studying the geologic history of abandoned channels that cross the fold. She relates larger changes in the river and fill of these abandoned channels to more severe earthquakes. She estimates that an earthquake about A.D. 850 did not change the river very much in this area. Earthquakes in about A.D. 1470 and in 1811 changed the river and sedimentation a lot.

"The geologic slate is periodically wiped clean by the river and it has eroded all sediment older than 2,400 years along the Reelfoot scarp. We will not find evidence for older earthquakes in this area." Guccione said.

In 1811-1812, the New Madrid earthquakes rocked North America's interior, ringing bells in Boston and temporarily reversing the flow of the Mississippi River. Scientists today have focused their efforts on determining the frequency and intensity of past earthquakes to better determine the possibility of future quakes. Guccione has received funding from the U.S. Geological Survey, which has intensified its efforts to study the New Madrid Seismic Zone since 1990

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