Earthquakes In Southeastern United States, Scientists Offer ‘Probable’ Explanation

Scientists recently gave a likely explanation for the unusual activity of earthquakes taking place in the southeastern part of the U.S., according to reports. The region has witnessed some notable seismic activities, the most recent of which occurred in 2011 when a 5.8 magnitude earthquake in Virginia's Mineral area shook the national capital too. As per the scientists, the periodical breaking of mantle pieces under the area, a process taking place since the past 65 million years at least, and their subsequent sinking into the earth may be the underlying cause for the increased seismic activity.

According to a recent report, the Southeastern area should ideally be a comparatively quiet zone in terms of seismic activity, due to its location in North American Plate's interiors. The zone is situated far away from the usual plate boundaries where earthquakes take place. However, the breaking and sinking cycle thins and weakens the remaining plate, which increases its tendency to slip that subsequently leads to earthquakes. The researchers suggested that the process in ongoing and may result in more future earthquakes. "Our idea supports the view that this seismicity will continue due to unbalanced stresses in the plate," said Berk Biryol, seismologist from University of North Carolina (UNC), Chapel Hill."The [seismic] zones that are active will continue to be active for some time."

The hazards that earthquakes in the center of plates pose are usually difficult to quantify as the reason for their occurrence is not well known. The new observations could, therefore, help researchers to better understand the dangers of such type of earthquakes. It is rare for earthquakes to take place in the center of plates, but they do occur when ancient faults or rifts beneath the surface reactivate, causing the area to slip and result in seismic activity. The area of southeastern United States is more than 1700 kilometers from the North American Plate's nearest edge, which covers the whole of North America, Greenland and areas of the Arctic and Atlantic oceans.

To figure out what was taking place deep under the earth's surface, the team of scientists from UNC created 3D images of North American Plate's mantle part, in particular the region under the east of the Mississippi River and south of the Ohio River, using tremors caused by earthquakes more than 3541 kilometers away. Consequently, it was found that the plate thickness was uneven in southeastern US, and not stable as was previously thought, with thick areas of older, dense rocks that stretched downward and thin areas of younger, less dense rocks.

The scientists first thought that the older and thicker rocks were remnants of ancient tectonic plates, however the thinner and younger rocks suggested otherwise. The researchers concluded that regions of the North American Plate became denser and gravity pulled them downward into the mantle as a result of the past rifting and accretion. According to the scientists, the phenomenon is the underlying cause of earthquakes in the otherwise stable area, and their occurrence will continue in the future.