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