We Might Still Feel Aftershocks From 1800s Quakes

So finds a new study that looked at three historical North American quakes
By Kate Seamons,  Newser Staff
Posted Nov 23, 2023 12:50 PM CST
Aftershocks Can Come Centuries Later
   (Getty Imges / Michael H)

If you live around the Missouri-Kentucky border and have experienced an earthquake, there's a roughly 30% chance it was an aftershock from a trio of quakes that struck the area between 1811 and 1812, or so says a new study. The Guardian reports on the research into the lifespan of aftershocks, and the results might surprise: The researchers say some areas can experience aftershocks decades or even centuries after the original event. To determine that, they zeroed in on three historical quakes that are thought to have measured 6.5 to 8.0 in magnitude and occurred within the "stable continental interior of North America."

They looked at the aforementioned Missouri-Kentucky quakes along with one that hit south-east Quebec in 1663 and an earthquake in Charleston, South Carolina, in 1886. As a press release explains, "The stable continental interior of North America is located far from plate boundaries and has less tectonic activity than regions close to plate boundaries, such as North America's west coast. As a result, the three study areas don't encounter earthquakes often, raising even more questions about the origins of their modern seismicity."

Writing in the Journal of Geophysical Research, researchers explain they used the "nearest-neighbor method to identify long-lived aftershocks." The method looks at the "time, distance, and the magnitude of event pairs, and [tries] to find the link between two events—that's the idea," says study author Yuxuan Chen said. "If the distance between a pair of earthquakes is closer than expected from background events, then one earthquake is likely the aftershock of the other." They found the aftershock activity of the 1663 Charlevoix, Quebec, earthquake has ended, but as with the Missouri-Kentucky quakes, the "aftershock activity of the 1886 Charleston earthquake in South Carolina is significant and continuing," with about 16% of quakes likely aftershocks from 1886. (More discoveries stories.)

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