The New Madrid Seismic Zone and possible impacts to the Tri-States

Through November, 2017 was a banner year for earthquakes. Most recently, a powerful 7.3 struck the Iraq and Iran border just this week killing more than 500 people, and earlier this year, a 7.1 hit Mexico City killing over 300.

This raised a lot of questions by Tri-State residents about the very active fault line in southern Missouri. About 150 earthquakes strike this area each year, more than 4,000 since the 1974.

In the small southeast Missouri town of New Madrid, a historical museum has a detailed account of the town's claim to fame; or infamy depending how you look at it.

"Seventy to 80 percent of people that come in here in a given year are coming because they heard about the earthquakes," said Jeff Grunwald, administrator at the New Madrid Historical Museum. "Now of those, I would say maybe half know we still have earthquakes."

In recorded US history, the New Madrid Seismic Zone is the center of numerous strong earthquakes, the most recent of which were back during what's referred to as the 1811-1812 Earthquake Sequence.

Three earthquakes measuring somewhere between 7.0 and 8.0 magnitude hit this area. If the earthquake was in the higher-end of the estimates, it would surpass the 1906 San Francisco earthquake measuring 7.8.

The first struck on December 16, 1811, estimated between 7.5 and 7.9 in magnitude. The second occurred just over a month later on January 23, 1812, estimated between 7.3 and 7.6. The third and final in the sequence struck two weeks later on February 7, 1812. That's when the 7.5-8.0 estimated quake hit.

The earthquakes were felt hundreds of miles away, as far as Washington D.C. The reason why it was felt for such a large distance lies miles beneath the ground we walk on.

"The bedrock is more dense down there several miles," Grunwald said. "It has less fracturing. What you have here is a more dense, stable medium through which these waves can travel."

Those earthquake shock waves can travel hundreds of miles right up the Mississippi River Valley toward the Tri-States.

"(In) New Madrid, no plate boundaries (are here)," Grunwald said. "We're a bit of an anomaly, therefore geologists love to study us."

So how would a large earthquake impact the Tri-States? The Missouri State Emergency Management Agency put together maps of projected earthquake intensities and possible damage using what's called the county-based Modified Mercalli Intensity Scale.

While a significant 7.0 or greater magnitude earthquake is not likely in the lifetime of inhabitants of the area, a moderate 6.0 or greater is possible.

Based on the intensity scale, poorly built or badly designed buildings would suffer considerable damage, while even well-built buildings may see slight damage if a 6.7 magnitude quake were to strike.

In the event of a jump of a magnitude higher to 7.7, 10 times stronger than a 6.7 (31 times the energy), even ordinary substantial buildings may partially collapse.

Normal home insurance does not cover earthquake damage. However, there are additional premiums though that do.

"In (the Tri-State area), there are certain risk factors you look at," said Sara Bruns, an insurance agent at Quincy's Shelter Insurance. "Whether earthquakes, or water backing up in your basement, or things that may be common in this area... if you know it's not covered, you know you want to talk to a client about that."

The American Red Cross recommends having emergency kits on hand, not just for earthquakes, but for any disaster.

One gallon of water per person per day, for two weeks, should be on hand. A two-week supply of non-perishable food should also be in your home with a can opener. In addition, a flashlight, hand-crank radio, extra batteries and a first aid kit with needed medication should be in reach.

The Red Cross also recommends a change of clothes, money, copies of important paperwork, blankets, sanitation supplies and pet food if you own a pet.

"Within the next 50 to 75 years, you could be looking at the possibility of having a 6.0 magnitude type quake," Grunwald said. "This would cause some damage, it would cause some problems, (but) probably not going to be a history changing type disaster."

While a moderate 6.0 magnitude earthquake is possible in our lifetime, the possibility of one of the powerful 7.0 or greater quakes one in every 500 to 1000 years.

Research shows there were a few strong past quakes, one in approximately 1450AD, 900AD and the year 490. AD. Those years are approximate based on geological research.