Aftershocks can often occur hours or days after an earthquake, sending additional tremors through the earth. However, new research suggests that some modern earthquakes may be aftershocks themselves from some of the strongest earthquakes recorded in the 1800s.
A new study, which was published in the Journal of Geophysical Research: Solid Earth, says that there may have been frequent aftershocks from a trio of quakes that occurred near the border of Missouri and Kentucky between 1811 and 1812. Further, a separate quake felt in Charleston, South Carolina in 1886 could also be continuing today.
These particular regions are especially problematic as the nature of their seismic activity is now well understood. Scientists typically measure the time, distance, and magnitude of event pairs to figure out if there is a link between two quakes. If the distance is close enough, then it’s likely that one quake is an aftershock of another.
While looking at many of the modern earthquakes felt near the Missouri-Kentucky border between 1980 and 2016, researchers found that 30 percent might be aftershocks from the three major quakes that struck the area almost 200 years ago. The older quakes were registered between magnitude 7.3 and 7.5, and the newer ones all range from 2.5 to greater.
Additionally, the researchers say that around 16 percent of the modern earthquakes felt around the Charleston area could be aftershocks from the 1886 quake, which registered a magnitude of 7.0 when it struck. Of course, identifying whether these are just aftershocks or new quakes altogether is a tricky business. However, it does raise some additional questions about how we measure seismic data.
The scientists say that much of this theory that modern earthquakes are aftershocks comes from the overall spatial distribution. However, they say that even these closely knit earthquakes could be full-on new quakes themselves, as there are reasons they might be closely clustered together like so.
If they aren’t aftershocks, then it is likely that these quakes are part of an ongoing process of creep, which the scientists aren’t sure how to explain just yet.