Predicting when earthquakes will occur is the proverbial “Holy Grail” of geoscience. Witness the current debate over the famous San Andreas Fault – with one seismologist saying it’s “locked, loaded and ready to go” – and it’s plain to see how incredibly jumpy people are when it comes to the topic of when the next Big One will be.
A feature by The Atlantic highlights the fact there are many regions of the planet that have often been forgotten in terms of their earthquake potential. The New Madrid Seismic Zone (NMSZ), hiding beneath Middle America, is one of these, and there’s something incredibly strange about it: There’s no tectonic plate boundary in sight.
Generally speaking, if two tectonic plates are grinding past each other either in a vertical manner or a horizontal manner, then you’ll get an earthquake, so long as stress builds up. However, as new studies have shown, “mantle scars”, ancient tectonic plate boundaries, can be reactivated over time, and new seismic zones can be born.
The NMSZ is one such dormant zone, formed when the continental land mass we now recognize as the United States tried to severe itself into two pieces around 600 million years ago. It failed, but its scar remained, and it has occasionally awoken as the movement of tectonic plates around it cause it to rupture, if only slightly.
Between 1811 and 1812, three earthquakes struck the NMSZ, one of which was just shy of a magnitude 7.7. Along with multiple aftershocks, these tremors caused huge landslides, generated enormous cracks in the ground, drained lakes and briefly forced the Mississippi to flow backward. The seismic waves were able to travel through the older and denser rock in the region with brutal efficiency, and as such, the radius of seismic activity was 10 times that of the devastating 1906 San Francisco earthquake.
Image in text: a map of the NMSZ. USGS
The question, of course, is whether or not this enigmatic zone will be brought to life again, underneath a region of the US that has millions more in the firing line than there was in 1812. A major earthquake could potentially threaten swaths of at least seven states – Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee, and Mississippi – along this 240-kilometer (150-mile) fault system. One study suggests that a repeat today would displace 7.2 million people and cause infrastructural damage amounting to around $300 billion.
As noted by the United States Geological Survey (USGS), this zone is somewhat active, noting that the region has accumulated high amounts of stress. “It is the most seismically active area of the United States east of the Rockies,” they write in a 2009 report. Looking for surface deformation is perhaps a red herring, though – unlike fault zones, which regularly push the surface around even during the period between major quakes – the NMSZ will likely show little deformation until a major rupture occurs.
They conclude that, based on the available GPS data, that the 1811-1812 quakes have a recurrence time of around 500 years, so we should not expect the next sizeable one – around a magnitude 7.0 – until around the year 2300. However, they do warn that there is still a 10 percent chance that it will occur in the next 50 years. The chance of having a magnitude 6.0 quake along the NMSZ in the same time frame is up to 40 percent likely.
Memphis, Tennessee is right in the firing line. Natalia Bratslavsky/Shutterstock
It must be noted that there’s plenty of debate as to how active or dormant the NMSZ is, but it’s quite unlikely that a catastrophe in the Midwest is due anytime in the next few lifetimes. So when you see somewhat overhyped and overexcited headlines claiming that the “clock is ticking,” remember that the clock in question is likely to be ticking very slowly indeed.
[H/T: The Atlantic]