New tectonic plates could explain mysterious series of earthquakes in the Pacific
For more than half a century scientists have known that continents drift over the surface of our planet, and that the ocean floor tears apart in their wake, with magma from the mantle filling the gap.
At the other end of the process, where tectonic plates converge, oceanic plates plunge into the deeper mantle in a process called subduction.
On Tuesday, Jonny Wu of the University of Houston presented preliminary evidence of possible plate tectonics within the mantle to a joint conference of the Japan Geoscience Union and the American Geophysical Union in Tokyo.
Wu and colleagues believe they have discovered tectonic plates which subducted into the mantle millions of years ago, sliding horizontally inside a water-rich layer of the mantle known as the “transition zone,” which lies 440-660km below the surface.
These subducted plates appear to travel horizontally for thousands of kilometres at speeds almost as fast as plates move at the surface.
The plate movements may explain a mysterious series of very deep, large earthquakes known as the Vityaz earthquakes, which originated in the mantle between Fiji and Australia.
Just as in conventional tectonic plates at Earth’s surface, the bends and breaks in these subducted plates can generate earthquakes.
Wu and colleagues suggest that the Vityaz earthquakes could be due to the sliding of a subducted plate within the transition zone.
“Basically, 90% of Earth’s deep seismicity (more than 500km deep) occurs at the Tonga area where we’ve found our long, flat slab,” said Wu.
The discovery has been made possible by recent advances in seismology, which have allowed scientists to generate pictures of Earth’s interior using vibrations from natural earthquakes. ■