Researchers use seismic waves to show how they echo through the planet following an earthquake and reveal its internal structure like radar waves. There are zones where seismic waves slow to a crawl.New research from the University of Utah finds that these enigmatic and descriptively-named ultra-low velocity zones are surprisingly layered.
Modeling suggests that some of these zones may be Leftovers from the processes that shaped the early Earth remnants of incomplete mixing like clumps of flour in the bottom of a bowl of batter.Michael S. Thorne, associate professor in the Department of Geology and Geophysics, said that all of the features we know about in the deep mantle, ultra-low velocity zones represent what is probably the most extreme.
The study is published in Nature Geoscience and is funded by the National Science Foundation.Seismic waves as they ripple through the Earth after an earthquake, scientists on the surface can measure how and when the waves arrive at monitoring stations around the world. From those measurements, they can back-calculate how the waves were reflected and deflected by structures within the Earth, including layers of different densities.
Ultra-low velocity zones sit at the bottom of the mantle, atop the liquid metal outer core. In these areas, seismic waves slow by as much as half, and density goes up by a third. Scientists initially thought that these zones were areas where the mantle was partially melted and might be the source of magma for so-called “hot spot” volcanic regions like Iceland.