The origin of the precursor signals, which arrive ahead of the main seismic waves that travel through Earth’s core, has remained unclear, but research led by University of Utah geophysicists sheds new light on this mysterious seismic energy.

PKP precursors appear to propagate from places deep below North America and the western Pacific and possibly bear an association with “ultra-low velocity zones,” thin layers in the mantle where seismic waves significantly slow down, according to research published in AGU Advances, the American Geophysical Union’s lead journal. (The AGU highlighted the research in its magazine Eos.)

“These are some of the most extreme features discovered on the planet. We legitimately do not know what they are,” said lead author Michael Thorne, a U associate professor of geology and geophysics. “But one thing we know is they seem to end up accumulating underneath hotspot volcanoes. They seem like they may be the root of whole mantle plumes giving rise to hotspot volcanoes.”

These plumes are responsible for the volcanism observed at Yellowstone, the Hawaiian Islands, Samoa, Iceland and the Galapagos Islands.

Thorne’s team, which included research assistant professor Surya Pachhai, devised a way to model waveforms to detect crucial effects that previously went unnoticed. Using a cutting-edge seismic array method and new theoretical observations from earthquake simulations, the researchers developed, they analyzed data from 58 earthquakes that occurred around New Guinea and were recorded in North America after passing through the planet.

Their new method allowed them to pinpoint where the scattering occurred along the boundary between the liquid metal outer core and the mantle, known as the core-mantle boundary, located 2,900 kilometers below Earth’s surface.