Little known seismic zone could spell trouble for Upper South

CAPE GIRARDEAU, Mo. – When Hannah Ward moved to southeastern Missouri to study four years ago, earthquakes were the last thing on her mind – though she had heard rumors.

“I didn’t really know that much about it before I got here,” she said. “Just that it could happen – a big one.”

She is right. That “big one” could come from the New Madrid fault line, which runs through northern Arkansas, the “boot heel” of southeastern Missouri, southern Illinois and into Kentucky and Tennessee. Unlike more famous earthquake zones, like California’s San Andreas Fault, few people see massive tremors as a big risk in the American heartland.

But they should. It turns out that a “big one” in the Midwest may be more imminent than previously thought.

A recent study conducted by the U.S. Geological Survey and published in Earth and Planetary Sciences Letters reported that the seismic zone – which is famous among earthquake experts but little known to many of the general public, especially outside the region – continues to pose a significant threat to parts of the Midwest and beyond, despite its relative recent inactivity.

“There’s a hint that there’s something different about the New Madrid Seismic Zone deep in the mantle,” said Charles Langston, director of the Center of Earthquake Research and Information at the University of Memphis. “That part of the mantle is a bit weaker than the surroundings. If it’s weaker, it can’t support stress from the tectonic plates.”

Langston, who read the USGS study, said data suggest that a large earthquake of a magnitude-6.0 or higher may come to pass in the next 50 years. However, he noted there is no sure way to predict when an earthquake will occur.

Using a new technology, geologists were able to look at high-resolution images of the New Madrid fault, and found that there are weaker rocks significantly deeper in the earth’s mantle than in other similar seismic zones in the central United States.

Those rocks are more susceptible to movement and stress, and could produce larger quakes, according to a statement released by the USGS.

Ward, who made the move to Southeastern Missouri State University from her home in Kirkwood, Mo., to study education, is coming up on graduation at the end of this school year. However, four years later, earthquakes still aren’t on her radar. In fact, Ward said, her fellow students haven’t heard much in terms of preparation and spend more time worrying about tornadoes rather than earthquakes.

“It’s just there,” she said. “Nobody really acts like it’s a big deal.”

Ward said she vaguely remembers a small earthquake in Cape Girardeau last spring. Langston feels small tremors in Memphis every now and then. In November, a 2.6-magnitude earthquake centered near the town of Bonne Terre, Mo., shook the region.

But when it comes to earthquakes in Missouri, it is stories from the 19th century that always take the cake. In 1811 and 1812, four powerful earthquakes struck the region, which scientists believe approached 8.0 on the Richter scale. At the time, the largest settlement in the area was New Madrid, Mo., giving the fault line its name.

The earthquakes were so powerful that they altered the course of the Mississippi River. The region has changed drastically since then – Memphis and St. Louis have grown in population, and larger towns like Cape Girardeau have sprung up. Interstate natural gas pipelines pass through the fault zone, and there are several nuclear energy plants in the surrounding region, though not in the fault zone itself.

That’s why the next “big one” could be a real problem.

“Now when that may happen is somewhat unknown,” said Mark Hasheider, Assistant Fire Chief of Cape Girardeau. “But I think we, as an area, and we, as a community, do take it very seriously.”

In Cape Girardeau and other communities in the region, building codes are the first line of defense against earthquakes. Hasheider said that after California, it’s the New Madrid zone that has the highest standard of seismic-resistant building codes in the country. Even if the building itself wouldn’t survive a major seismic event, he said, the hope is that at least the construction standards set by codes would at least help protect the people inside.

Nevertheless, there’s still plenty of uncertainty about how best to prepare.

“A lot of these [codes] have yet to be proven,” Hasheider said.

Modern building codes haven’t been tested by the New Madrid fault. The largest earthquake in the region since the 1800s was 5.4-magnitude quake centered in southern Illinois in 1968. Even though seismic instruments have recorded thousands of earthquakes in the past few decades, most are too small to be felt.

Communities like Cape Girardeau won’t know until the “big one” if their preparedness was enough, but that doesn’t mean they aren’t emphasizing readiness. Hasheider added: “It’s not gone by the wayside.”

If and when there is a major seismic event in the New Madrid zone, the effects of the quake would reach farther than this part of the Upper South.

“There’s a mentality that only the facilities and people on top of the earthquake zone are going to be affected,” said Edgar Portante, a researcher at Argonne National Laboratory. “They don’t know that it’s going to extend all the way to the east.”

In 2009, at the request of FEMA, Portante and a team of scientists at Argonne studied the risk the New Madrid Seismic Zone posed to the country's transnational natural gas pipelines. There are ten interstate lines that pass through or near the New Madrid fault, leaving them vulnerable to a major seismic event, according to the study.

“The intensity of the [major] earthquake would probably break them,” Portante said. “Even if they were new.”

What makes the New Madrid zone especially prone to damage is the nature of the soil. Some soil in the region is susceptible to a geological phenomenon called soil liquefaction. When that soil is shaken during an earthquake, the ground’s ability to support structure fails.

“Even a little amount of shake, not even the highest, could cause the soil to liquefy and collapse,” Portante said. “If that were to happen, it could also break the pipeline, if it’s long enough.”

The study found that a major event in the zone with the potential to damage the pipelines could lead to significant shortages of natural gas supplied to states including Missouri, Illinois, Wisconsin, Indiana and Michigan. In some cases up, such a 30 percent reduction of gas supplied could spell trouble for customers, especially when trying to heat their homes in the winter.

“People say, ‘I’m here in, say, Pennsylvania. I won’t be affected.’ Of course you will be,” Portante said. “It’s kind of a wake up call to many people who are not conscious that they’re downstream.”