Most severe earthquake in 30 years a 'wake-up call' to New Madrid Seismic Zone

·5 min read
A researcher points to seismic data displayed on a computer screen in 2008 in St. Louis. A 4.0 magnitude earthquake in southeast Missouri last November was a wake-up call for those living in the New Madrid Seismic Zone, says Jeff Briggs, Missouri State Emergency Management Agency Earthquake Program manager.
A researcher points to seismic data displayed on a computer screen in 2008 in St. Louis. A 4.0 magnitude earthquake in southeast Missouri last November was a wake-up call for those living in the New Madrid Seismic Zone, says Jeff Briggs, Missouri State Emergency Management Agency Earthquake Program manager.

When a 4.0 magnitude earthquake occurred Nov. 18 about 4 1/2 miles south of Williamsville in southeast Missouri, it was even lightly felt in Columbia.

This was the most severe earthquake for the region since 1991 and was a wake-up call for those living in the New Madrid Seismic Zone, said Jeff Briggs, Missouri State Emergency Management Agency Earthquake Program manager.

The smallest earthquakes people generally feel are 2.5 magnitude. Earthquakes of 4.0 magnitude can cause moderate damage, with the largest in the 8.0 magnitude range, which is what happened at the New Madrid Seismic Zone in late 1811 and early 1812.

The New Madrid region sees about 200 small earthquakes per year, the Missouri Department of Commerce and Insurance reported.

Missouri's earthquake risk

"(We want to) outline the earthquake risk centering in southeast Missouri. It is one of the largest active seismic zones," Briggs said

Reports after the November earthquake in southeast Missouri noted car alarms were activated, photographs wobbled on walls, dishes were broken and a couple of buildings had structural damage, Briggs said.

"It was more of a scary event, more of a wake-up call for people in southeast Missouri than it was an extremely damaging event," he said.

If a similar earthquake were to happen in the region like those from from 210 years ago, the damage would be extreme throughout Missouri and the Midwest, Briggs said.

"We want people to be aware of the risks and to know how to prepare, because when that really big one does happen, we want to minimize the risks," he said.

The New Madrid Seismic Zone sees regular activity. The majority of earthquakes over the past six months measured between 1.0-2.0 magnitude, according to a recent earthquakes map from the University of Memphis Center for Earthquake Research and Information.

New Madrid Seismic Zone an enigma for researchers

There are at least two schools of thought regarding the New Madrid Seismic Zone, said Eric Sandvol, professor of geological sciences at the University of Missouri and vice chair of the Missouri Seismic Safety Commission. Sandvol has an emphasis in geophysics, tectonics and solid earth processes.

Some people believe there is no longer a chance for earthquakes as severe as those in 1811-12, while others believe we are about due for another major earthquake, he said.

"Those are both extreme positions," Sandvol said. "I understand both arguments. The problem is we don't understand these earthquakes. They are probably the most enigmatic earthquakes on the planet."

An October 2009 impact study conducted by the Mid-America Earthquake Center, with the Federal Emergency Management Agency, notes if the three fault segments in the seismic zone rupture in a single event, it could result in a 7.7 magnitude earthquake.

An estimated 715,000 buildings in an eight-state region would be damaged, including 130 hospitals. There possibly would be as many as 86,000 casualties and direct economic impacts of $300 billion within the region, the study found.

The New Madrid Seismic Zone is unique, though, because by all accounts it should not even exist in the first place, Sandvol said.

"The (fault) is not even supposed to be there, according to standard plate tectonic theory," he said.

There are interesting theories as to why earthquakes happen in this seismic zone, but they are not yet well-supported by evidence, Sandvol said.

It is a bad idea to give predictions about when a major earthquake event could happen, he added.

"That is the main message to know. These are not like your typical earthquakes in California or Japan or Tonga," he said. "Because we do not understand the (New Madrid) earthquakes very well, that is why there is a wide range of opinions on them."

The majority of earthquakes occur at the edges of large and relatively rigid tectonic plates because of their motion against each other, Sandvol said. In the case of New Madrid, it is in the middle of a tectonic plate.

"You are nowhere near a plate boundary," Sandvol said. "So where is that (earthquake) energy coming from?"

Other regions have seismic zones that aren't near plate boundaries, but there are more easily defined reasons for earthquakes happening there than at New Madrid, he said.

Limited resources available to explain New Madrid earthquakes

So if there are so many conflicting opinions on why New Madrid has earthquakes, is more research being done to explain their cause?

The answer is both yes and no.

Research is being done on the New Madrid Seismic Zone, but the degree to which it is done is limited based on funding availability.

"Doing science can be an expensive thing," Sandvol said. "The (United States Geological Survey) and its Earthquake Hazards Program is always underfunded."

Sandvol has seen funding resources decline over the past 10 to 15 years. The Earthquake Hazards Program in fiscal year 2021 saw a budget reduction of $24.5 million.

Most of the research on New Madrid is older, but that does not mean there is not any new research done, he added.

This includes surveying land movement on the sides of the fault zone to see if there is an accumulation of energy. There also is the general earthquake monitoring system.

Sandvol's research involves earthquake imaging, similar to a medical CT or PET scan.

"We take pictures of the inside of the earth and we want to look and see if we can see something interesting about the structure inside New Madrid," he said.

He was a co-author on research into what is known as site amplification. Areas with softer soil, such as near a river, will feel a more severe ground shake than areas closer to hard rock.

The City of New Madrid's southern border is the Missouri River. The 1811-12 earthquakes caused it to flow backward.

This article originally appeared on Columbia Daily Tribune: Southeast Missouri earthquake in November 2021 prompts safety seminars