Ash from an undersea volcanic eruption, part of the uninbabited islet of Hunga Ha’apai, 63 km northwest of the Tongan capital Nuku’alofa. 90% of the Earth’s deep seismicity occurs in the Tonga area in which scientists think they have found a subducted plate. Photograph:

Preliminary findings suggest that a mysterious series of earthquakes in the Pacific could be down to previously undetected plates

Scientists say they have found a possible layer of tectonic plates within the Earth’s mantle which could explain a 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.