Earthquake reveals path of potential hotspot under North America

Nature : A mantle plume appears to have left its mark underneath the North American tectonic plate as it drifted west over the last 100 million years. When such plumes occur in the ocean, they often produce island chains such as the Hawaiian Islands. Under continental plates, they leave a trail of heated rock behind them. Risheng Chu of the Institute of Geodesy and Geophysics in Wuhan, China, and his collaborators believe they have found such a trail. They studied seismic wave data following the 23 August 2011 earthquake centered in Virginia. Using the USArray network, they found that seismic waves from the earthquake arrived at seismometers in the midwestern US later and with lower intensity than expected. That suggested a band of warm rock, which slows and weakens seismic waves, probably runs from east to west approximately 200 km below the surface of Kentucky. That depth corresponds roughly with the bottom of the North American tectonic plate. A similar effect was found northeast of the epicenter. Chu’s team believes that the bands of warm rock are part of a single line caused by a hotspot that is now located in the mid-Atlantic.