New Madrid Seismic Zone

The bulk of seismic activity on the New Madrid fault impacts Arkansas, Tennessee and southeast Missouri. It is the most active seismic area east of the Rocky Mountains.

The theory of plate tectonics would suggest that the central and eastern United States, including the New Madrid Fault Zone centered in southeast Missouri, should have no earthquakes at all.

Nevertheless, the New Madrid earthquakes that shook significant parts of the country in December 1811 and February 1812 were among the most powerful in the U.S. east of the Rocky Mountains, with magnitudes between 7.3 and 7.5. The three major earthquakes and their aftershocks rumbled across Missouri, Tennessee and Arkansas, causing sand eruptions, landslides and even backward flow of the Mississippi River.

Although the New Madrid Fault itself cuts across the Missouri Bootheel and enters Tennessee and Arkansas, the larger seismic zone includes parts of five other states: Illinois, Indiana, Kentucky, Oklahoma and Mississippi.

Recent earthquakes in California’s Mojave Desert, which registered 7.1 and 6.4 on the Richter Scale, have reminded some residents of the Midwest what can happen in a seismic zone. Quakes that happen here, however, differ from those in California.

Mian Liu, chair of Geological Sciences at MU, said the California quakes are unlikely to trigger any trouble in the New Madrid area.

“It is a different fault system, and we don’t know any existing mechanisms that could link these two places,” Liu said.

California earthquakes are common along the well-known San Andreas fault between the Pacific and North American tectonic plates. The July 4 -and 5 earthquakes, however, happened along smaller, individual fault lines.

MU geology professor Eric Sandvol, who researches seismology, explained the causes of earthquakes.

“We live on this planet that is made of puzzle pieces, and the puzzle pieces are moving all the time,” Sandvol said. “Those puzzle pieces are called plates. Tectonic plates.”

Earthquakes happen when the Earth’s crust breaks, and it always breaks quickly because it is bending. Seismologists use GPS to measure movement in the Earth’s crust and the bending that occurs with it.

“We can see it in California; that makes perfect sense,” Sandvol said. “The very strange thing is we don’t see that bending process here in Missouri.”

He said professionals have been making measurements in the New Madrid area for nearly 30 years and have seen no bending. The science surrounding the seismic zone, however, is heavily debated.

A number of researchers and professionals predict there will be no more earthquakes in the New Madrid area. But Paco Gomez, associate professor at MU’s Department of Geological Sciences, said that given the power of the early 19th-century quakes, it’s important to consider how often such large temblors have happened as a means of forecasting the likelihood of similar earthquakes in the near future.

Gomez’s research looks at how often faults repeat the production of large earthquakes. By examining sand deposits, he can determine how often quakes repeat along a fault on average. Although he hasn’t researched the New Madrid zone specifically, other scientists have.

In the New Madrid area, large quakes appear to happen about every 500 years based on geological information from the past two millenniums. Smaller events happen more frequently, though.

“Based on that assumption, the other experts have estimated the probability of large events within the next 50 years,” Gomez said. “Earthquake statistics suggest that, even if the probability of a large earthquake is very remote, there is a reasonable likelihood for a moderate (magnitude 5.5 to 6.0) earthquake, which could still be damaging.”

Liu explained the difference between a prediction and a forecast.

Earthquake predictions require three elements simultaneously: time, place and magnitude. “So, long story short, at the present time scientists cannot make earthquake predictions. All the claims of predictions are questionable.”

Forecasts, on the other hand, are assessments of probability. So instead of saying when and where a 7.0 quake might happen within the next 50 years, forecasts merely estimate what the chances of that happening are.

Liu said that the science surrounding the New Madrid Fault is controversial and that there are all kinds of different data and models.

Although forecasts aren’t perfect, they’re useful for planning risk and hazard assessments.

So, what would happen if a large quake struck along the New Madrid Fault today?

Data on the impact of the 1811-12 New Madrid earthquakes all comes from east of the Mississippi River, given that there were few settlements to the west. Although the quake was felt as far east as Boston, major effects were limited to areas very close to the fault.

Sandvol said that if we assume the impact of another quake would be symmetrical, Boone County could expect strong ground shaking, some fallen tree limbs and some minor damage to buildings. Metro areas such as St. Louis and Memphis, Tennessee, could have catastrophic damage. He would expect widespread liquefaction and building collapses.

Sandvol, who is a member of the Missouri Seismic Safety Commission, said he worries about bridges failing and about schools and hospitals.

“We are trying to help the state prepare, but there’s funding limitations,” Sandvol said. “We can’t retrofit all the bridges in the state. It’s a billion-dollar proposition.”

The Missouri Seismic Safety Commission was established by the legislature in the early 1990s to make recommendations to the government and the public on how to better prepare for a seismic event. It also provides the rapid visual screening program, which sends engineers to review the structural integrity of schools in earthquake zones.

Authorities throughout the New Madrid zone, including in Boone County, have been encouraging people to prepare, even if it’s uncertain whether a quake will occur in the near future.

“This is the most enigmatic earthquake zone on the planet ... ,” Sandvol said. “There’s a lot of things scientists are still working on to try to understand it.”

  • General assignment reporter, Summer 2019. Studying Magazine Design. Reach me at kkxq2@mail.missouri.edu, or in the newsroom at 882-5700.

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