Scientists from UCLA and UC San Diego have found pockets of molten rock deep inside a region of Earth where they did not expect to find any, according to a report in today's Nature. John Vidale of UCLA and Michael Hedlin of UC San Diego analyzed seismic waves from 25 earthquakes, magnitude 6.0 or higher, that have struck the southwest Pacific island of Tonga since 1975. More earthquakes have hit that area than anywhere else on Earth.
"The strength of the scattering is the biggest surprise," Vidale said. "The best, and perhaps only, explanation for the large amount of scattering in the seismic waves is that part of the rock in the mantle is melted." The study detected molten rock across a 300-by-600-mile region deep beneath Tonga. Geologists had previously believed that Earth's mantle was solid rock.