Earthquakes vs. aftershocksThe modern seismic activity the researchers studied is likely a mixture of aftershocks from the big quakes from the 1800s and background seismicity, Chen said. “Are small earthquakes in the New Madrid seismic zone aftershocks of 1811-1812 or not?” Hough said in an email. “The new study considers the question from a different angle, considering how tightly clustered earthquakes are, and concluding that some of the events are ongoing aftershocks,” Hough said. Aftershocks might still be continuing, but once the normal seismic rate for the area returns, she said, you can no longer identify them as aftershocks. “For this reason, we seismologists sometimes disagree about which earthquakes are foreshocks or aftershocks,” Ebel said, “and I think those disagreements are inherently unresolvable.”

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Persons: —, ”, Yuxuan Chen, geoscientist, Chen, “, Susan Hough, Hough, ” Hough, “ We’ve, . Fuller, Morgan Page, John Ebel, Ebel, John Karl Hillers, ” Ebel Organizations: CNN, Missouri -, of Geophysical Research, Wuhan University, Earthquakes, US Geological Survey, Survey, . Geological, USGS Earthquake Science, Boston College, . Geological Survey, San Locations: States, Missouri, Missouri - Kentucky, Charleston , South Carolina, Madrid, Memphis, Mississippi, Charleston, North America, China, New Madrid, Chickasaw, Reelfoot Lake , Tennessee, Boston, California, Eastern North America, Southern California, Northern California, San Andreas, Central