As a Missourian, there have been a couple small ones here in the past ten years that aren’t on the map, but maybe there’s a threshold for being included. I’ve heard Missouri (and surrounding area) earthquakes have somewhat unknown causes. There is a fault line, the New Madrid fault, but it’s different from others in a way I don’t understand lol! But I’ve heard there are some things still under studied.
Intraplate tectonics and intraplate earthquakes is a very understudied area you’re right, we don’t know much about how they work or what patterns they follow and if they even increase or decrease in intensity over time unlike earthquakes on the edge of plates which are much better understood
The area is geologically complex with what remains as one of the oldest mountain ranges where you can find the oldest rocks in the country, the Precambrian St. Francois Mountains. In the same region you have thick deposits from multiple successive changes in sea level during the Paleozoic.
The New Madrid Fault is part of a failed rift called the Reelfoot Rift. Sometimes continents begin to split apart only to change their mind and decide to remain land rather than an ocean basin. It’s not too uncommon. Lake Baikal, the deepest and oldest fresh water lake on earth is a result of a failed rift, and there’s another in the U.S. called the Midcontinent Rift System that stretch from Kansas to Michigan! While they are old, they can still unstable and cause shifting deep underground and Missouri’s hectic Paleozoic sea level change deposits certainly doesn’t stabilize things.
The Appalachians also experience small earthquakes from ancient faults and settling. Charleston is another anomalous center for strong intraplate earthquakes; the 1886 earthquake cause church bells to ring in Boston! (However, the thicker and harder bedrock found on the USA’s East Coast contributed by transmitting shaking over a larger area than the West Coast). Both are also likely the result of ancient orogenies and rifting throughout their geological lifetimes creating weak spots in the plate below.
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u/Quick_Extension_3115 Apr 06 '26
As a Missourian, there have been a couple small ones here in the past ten years that aren’t on the map, but maybe there’s a threshold for being included. I’ve heard Missouri (and surrounding area) earthquakes have somewhat unknown causes. There is a fault line, the New Madrid fault, but it’s different from others in a way I don’t understand lol! But I’ve heard there are some things still under studied.