Today’s earthquakes could be aftershocks from centuries-old quakes in the 1800s, a new study reveals.
Back in the 19th century some of the strongest earthquakes in recorded US history struck North America’s continental interior.
Scientists from the American Geophysical Union believe that almost two centuries later, the central and eastern United States may still be experiencing aftershocks from those events.
While aftershocks are smaller in magnitude than the main shock, they can still damage infrastructure and impede recovery from the original earthquake.
Lead author Dr. Yuxuan Chen said: “Some scientists suppose that contemporary seismicity in parts of stable North America are aftershocks, and other scientists think it’s mostly background seismicity.
“We wanted to view this from another angle using a statistical method.
“You use the time, distance and the magnitude of event pairs, and try to find the link between two events — that’s the idea.
“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.”
The study, published in the Journal of Geophysical Research: Solid Earth, came to these conclusions as regions near these historic earthquakes’ epicenters are still seismically active today.
However, this is still not certain, it is possible that they are actually foreshocks preceding larger earthquakes or background seismicity.
The team studied three historic events in Canada, Missouri-Kentucky and South Carolina, looking at modern quakes within 250 kilometers (820210 feet) of the historic sites.
These three areas were chosen due to their distance from plate boundaries which raises suspicion about the origins of their modern seismicity.
The team focused on earthquakes that were greater than or equal to a magnitude of 2.5 because anything smaller than that is difficult to record.
Dr. Susan Hough, however, believes that they only have one piece of the puzzle.
She said: “In some respects, the earthquakes look like aftershocks if you look at the spatial distribution, but earthquakes could be tightly clustered for a couple of reasons.
“One is that they’re aftershocks, but also you could have a process of creep going on that’s not part of an aftershock process.
“Exactly what their results mean is still open to question.
“To come up with a hazard assessment for the future, we really need to understand what happened 150 or 200 years ago.
“So, bringing modern methods to bear on the problem is important.”
Results showed that the Canadian quake’s aftershocks had ended but the other two may well still be causing aftershocks.
Near the Missouri-Kentucky border, the researchers found that around 30 percent of all earthquakes from 1980 to 2016 were likely aftershocks from major historical earthquakes.
In Charleston, South Carolina, the team found around 16 percent of the modern-day quakes were likely also aftershocks from the 1800s.
Produced in association with SWNS Talker