Tina Niemi
Tina Niemi sports a T-shirt from a New Madrid, Mo., museum. –Photo by Dan Videtich

Examining the past

Niemi studies earthquakes by looking at buried features and dating the surfaces where earthquakes are recorded in the subsurface sediments. “In the Mississippi Valley and surrounding areas, the data researchers collected along the NMSZ show earthquakes occurred around 1450 A.D. and 900 A.D.,” she says. Native Americans lived on some of the earthquake features during this time, helping researchers date the surface because of the artifacts and materials they left behind. The next earthquake came along and buried it. In the NMSZ, researchers have found artifacts on the surface of the sand blows located along the swampy bottomland of the Mississippi River.

This kind of geologic evidence means the earthquakes were large. “A magnitude 4 earthquake won’t leave evidence in the soil,” Updike says. “But if it’s a magnitude 7, it will leave fingerprints in the sediments that scientists can recognize.” Because there’s physical evidence of the 1811-12 earthquakes along with others in the soil, that means large earthquakes have occurred multiple times.

Looking at the future

Today, the areas potentially affected by a modern earthquake event in the NMSZ include Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi. “Whether it’s going to occur in the next two years or 20 years, we don’t know,” Updike says. “But it’s important that everyone who lives in that region has an understanding and is prepared.” Updike monitors earthquakes occurring all over the United States.

He says there’s a pattern of small concentrations of earthquakes occurring every year in the Mississippi Valley from Ohio and southern Illinois to Louisiana. “These earthquakes aren’t occurring in patterns like that in other places,” he says. To come to that conclusion, Updike adds evidence he collects to what was recorded in 1811-12. Then he combines that information with the ancient geologic evidence and careful measurements of changes in the earth’s crust and its dimensions. “All those things together give a strong indication that this is a place where big earthquakes can occur again,” he says.

Randall Updike on the job for the USGS near the U.S.-Mexico border.

When an event does strike the region, it will be different than what the public generally associates with another earthquake-prone area: California. The seismic energy in the NMSZ will travel greater distances because the sediment in the rock underneath the surface is composed of flat layers. Those layers transport seismic energy farther than in California, where the rocks are more contorted and not as uniformly solidified. “So in the central U.S., an earthquake could occur in southeast Missouri and be felt strongly in Kansas City or in St. Louis, but in California, at those distances, you wouldn’t feel as much,” Updike says. “There would be a bigger area affected in New Madrid, and a magnitude 7 there could be more destructive than a magnitude 7 in California.”

The level of destruction would also be different, because in California, codes demand that buildings withstand such an event. In most places along the NMSZ, the buildings were built without any consideration of earthquakes. “So they will not do as well in general,” Updike says. “They won’t withstand an earthquake and that means it’s more dangerous for the people living there.”

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