I’m probably going to get some things wrong here, really infuriating any geologists reading this blog. To which I say? Good. Our geologist readers have had it too easy.
211 years ago, the ground in and around New Madrid, Missouri shook, and it shook hard. The happenings comprise four of the nine or ten largest earthquakes to ever hit the contiguous United States, plus hundreds of aftershocks felt as far away as the Atlantic coast. It was one of the most extreme natural disasters in American history, and if it happened again today, it could be the deadliest. Thankfully…well, not much to be thankful for. Experts have some ideas about when it could happen again (as of 2009, the U.S. Geological Service gave an earthquake of similar severity a seven to ten percent chance of happening in the next fifty years), but science isn’t great at predicting earthquakes yet. And these are a little harder than Californian earthquakes to predict. Because scientists don’t know why these happen.
Theories abound, of course, about the why behind the New Madrid Earthquakes, and research is ongoing. But geologists’ current model of plate tectonics doesn’t have a perfect answer for earthquakes in the middle of a continental plate. They know there are fault lines below New Madrid, and they seem to have a pretty good idea of how they got there, but they don’t know what makes them move.
The fault lines were formed, it seems, when North America was pulled in multiple directions during a recent (750 million years ago) supercontinental breakup. A rift formed then, and while it didn’t actually break the plate apart, the weakness is still there, maybe like a piece of cloth that’s been stretched and seen a few stitches pop. This isn’t the only place in the world these sorts of fault lines exist, or even the only place on this plate. There was another huge 1800’s intraplate earthquake in Charleston, South Carolina. From my own internet searching, it doesn’t seem they know what caused that one, either, but its fault lines are a lot more inactive than those of New Madrid.
Since 1974, more than four thousand earthquakes have been recorded around New Madrid, and while most are too small to even be felt, not all of them are. Growing up in northern Illinois, I remember a few, though I usually needed someone to explain to me that that’s what had just happened. Two days ago, there was a magnitude 2.5 quake epicentered near Dyersburg, Tennessee.
Massive earthquakes can happen in the eastern half of the United States, and we don’t really know why. One of those complications that exists from your ground sliding around on a bed of hot rock.
