Puzzling features deep in Earth's interior illuminated by high resolution imaging

The University of Cambridge is the first to take a detailed image of an unusual pocket of rock at the boundary layer with Earth's core.

The enigmatic area of rock, which is located almost directly beneath the Hawaiian Islands, is one of several ultra-low velocity zones because earthquake waves slow to a crawl as they pass through them.

The research published today in Nature Communications is the first to reveal the complex internal variability of one of these pockets in detail.

These are the most fascinating and complex deep interior features. The first solid evidence to show their internal structure is a real milestone in deep earth seismology.

The iron-nickel core is surrounded by a thick layer known as the mantle, and on top of that a thin outer shell. The mantle is very hot and can flow very slowly. The internal currents feed heat to the surface and cause the movement of plates and volcanic eruptions.

The echoes and shadows of earthquakes reveal radar-like images of deep interior topography. Images of the structures at the core-mantle boundary have been difficult to see and are important for studying our planet's internal heat flow.

The researchers used the latest numerical modeling methods to show kilometer-scale structures. The methods developed by Dr. Kuangdai Leng at the University of Oxford are pushing the limits of modern high- performance computing for elastodynamic simulations.

The speed of waves traveling at the base of the ultra-low velocity zone was reduced by 40%. It is possible that this iron-rich material is a remnant of ancient rocks from Earth.

The new research could help scientists understand what sits beneath and gives rise to volcanic chains like the Hawaiian Islands. There is a correlation between the location of the hotspot volcanoes and the ultra-low velocity zones at the base of the mantle. The most popular theory is that the hot mantle material comes from the core-mantle boundary to the surface.

With images of the ultra-low velocity zone beneath Hawaii now in hand, the team can gather rare physical evidence from what is likely the root of the plume feeding Hawaii. Their observation of dense, iron-rich rock beneath Hawaii would support surface observations, and the basalts that have erupted from Hawaii have anomalies which could either be an early-Earth origin or core leaking, it means some of this dense material piled up at the base must be dragged.

More of the core-mantle boundary needs to be imaged to understand if there is a pocket of dense material at the base. Where earthquakes occur and where seismometers are installed can affect where the core-mantle boundary can be targeted.

The team's observations add to a growing body of evidence that Earth's deep interior is just as variable as its surface.

They plan to use their techniques to improve the resolution of other pockets at the core- mantle boundary. They hope to map the geological landscape across the core-mantle boundary and understand its relationship with the dynamics and evolutionary history of our planet.

More information: Kilometer-scale structure on the core–mantle boundary near Hawaii, Nature Communications (2022). DOI: 10.1038/s41467-022-30502-5 Journal information: Nature Communications Citation: Puzzling features deep in Earth's interior illuminated by high resolution imaging (2022, May 19) retrieved 19 May 2022 from https://phys.org/news/2022-05-puzzling-features-deep-earth-interior.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.