After a series of earthquakes along New Madrid fault line, will we see 'The Big One?'

ST. LOUIS - Earlier in the month, Missouri and nearby states saw a string of small earthquakes triggered along the New Madrid fault line. It raises the question many have had: Will the New Madrid fault line see "The Big One" anytime soon?

"The Big One" refers to a massive earthquake that is anticipated to cause catastrophic destruction. This fear is commonly discussed along the San Andreas fault line in California. However, some have also brought up the same concept for the New Madrid fault line, which sits right along the state lines of Arkansas, Tennessee, Kentucky, Missouri, and Illinois.

Have no fear right now, though. According to Dr. Thomas Pratt, a research geophysicist at the U.S. Geological Survey, they only predict a seven percent chance of a magnitude 7 earthquake within the next 50 years.

"Large (M7) earthquakes occur about every 500 to 600 years in the New Madrid seismic zone, but there is a lot of variability in the timing, so they could come much sooner," Pratt said. "So, we don't 'expect' a major earthquake in the next 50 years, but there is a chance there could be one."

On Dec. 9, there were six small earthquakes (3.0 magnitude or less) detected in Missouri's bootheel, all within about a seven and a half-hour span.

Most of them were too small to feel in person, but seismic instruments detected them. Some have raised the question if these smaller earthquakes could relieve some of the pressure from the New Madrid fault zone, decreasing the chance of a larger one. Pratt says it depends.

"Each small earthquake relieves a tiny amount of stress on the fault it occurs on, but each earthquake also increases the stresses on nearby faults. It is thus not clear that these small earthquakes have a net effect of reducing the chances or increasing the chances of a larger quake; it depends on which faults have a reduction in stress and which ones have an increase," he said.

The last extremely large earthquake the fault line had was between 1811 and 1812, through a series of three or four magnitude 7 and 8 earthquakes. The damage left settlements destroyed, including the Great Prairie, bank failures along the river, and even made the Mississippi River flow backwards.

Seismic activity is ongoing along the New Madrid fault line. In the 1990s, a few magnitude 4 earthquakes were reported, and there have been a few more larger than that, according to Pratt.

While there is no set timeline of when large earthquakes should be occurring along the New Madrid fault, Pratt said that for every magnitude 7 earthquake, USGS expects about 10 magnitude 6 earthquakes, which translates into a magnitude 6 earthquake potentially anticipated around every 50 years.

"We can 'forecast' earthquakes, but we cannot predict when the next one will occur. They are not regular in time," Pratt said. "I like to use a baseball analogy—we can say that a hitter hits a home run on average every 10 at-bats, but we cannot tell you whether he will hit three in a row or not have any for a while. Thus, we can tell the chances of earthquakes in a broad sense, but we cannot tell you when the next one will occur."

While the predictions aren't favorable for a large-scale earthquake soon, Pratt reminds residents that they should always remain aware and diligent in the event it does occur.

"Be prepared for an earthquake. Have some emergency supplies on hand; try to make your house 'earthquake-proof' by bolting it to its foundation and making sure there are not heavy objects that can fall on people (like heavy objects on top of large bookcases). It is falling objects that injure people during earthquakes, so we advise 'drop, cover, and hold' if you feel an earthquake; get under a table or desk so that objects do not fall onto you," he said.

To learn more about the New Madrid fault and seismic zone, click here.