The North American Plate consists of North America, Greenland, and parts of the Atlantic and Arctic oceans. The southeastern United States is fairly distant from its active margins, the closest being a little more than 1,000 miles away. Sometimes, however, the region faces seismic events. In 2011, a rare 5.8-magnitude earthquake was felt from New England to the Carolinas.
Publishing in the Journal of Geophysical Research—Solid Earth, a group of researchers postulated that recent seismic activity in the region can be linked to pieces of the mantle breaking off and sinking into the Earth.
Berk Biryol, the study’s lead author and a seismologist at University of North Carolina—Chapel Hill, said this means the region will remain seismically active for some time.
To glimpse beneath the Earth’s surface, the researchers created a 3D model of the area of interest. “Seismologists image the interior of the Earth by tracing the paths of seismic waves created by earthquakes as they move through the ground,” according to American Geophysical Union. “These waves travel faster through colder, stiffer, denser rocks and slower through warmer, more elastic rocks.”
The region, the researchers found, was fairly uneven, consisting of both thick, old areas and thin, young rock.
“Based on the distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere,” the researchers wrote.
The dense tectonic plate areas that foundered sank into the asthenosphere due to gravity. The asthenosphere sits just below the lithosphere and is a highly ductile and viscous area. Once the thick region was gone, the asthenosphere filled the mantle’s void, eventually tuning into the thin rock.
This process, the researches hypothesized, produces the region’s earthquakes.
“This region has not been active for a long time,” Biryol said in a statement. “We were intrigued by what was going on and how we can link these activities to structures in deeper parts of the Earth.”
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