Seismic waves reveal giant structures deep beneath the Earth’s surface in the Marquesas Islands

Researchers at the University of Maryland in the United States have recently discovered giant structures in the depths of the Pacific Ocean, 2,900 km deep, between the Earth’s mantle and core.


We don’t know everything about the Earth’s core.

Scientists have discovered that there are giant structures about 2900 kilometres below the Earth’s surface. These as yet undiscovered structures lie at the boundary between the molten core and the Earth’s solid mantle. These structures are estimated to be about 1000 kilometres in diameter and about 25 kilometres deep. The discovery follows analysis by researchers at the University of Maryland in the United States of data from 7,000 recorded earthquakes, including major earthquakes, in the Pacific Ocean region between 1990 and 2018.


They discovered what they now call an ultra-low velocity zone (ULV), where seismic waves pass at slower speeds. However, scientists are not sure of the exact composition and arrangement of these structures. To do this, the scientists used a machine learning algorithm called Sequencer, developed by scientists at Johns Hopkins University and Tel Aviv University, who co-authored the study published in the June 12, 2020 issue of the journal Science.

The shear waves are talking.

Earthquakes with a magnitude of 6.5 or greater and a depth of more than 200 kilometres below the Earth’s surface have generated echoes as they passed through as yet undiscovered structures. These echoes are called « shear waves », and they were similar in several earthquakes, which distinguishes them from random noise.

By looking at thousands of core-mantle boundary echoes at the same time, instead of focusing on a few at a time, as we usually do, we got a whole new perspective, » said Doyeon Kim, a post-doctoral fellow in the Department of Geology at UMD and the lead author of the paper. « It shows us that the core-mantle boundary region has many structures that can produce these echoes, and that was something we hadn’t realized before because we had only a narrow view.

A better understanding of the planet’s evolution.

Scientists also claim that an area of ULV, previously thought to be under the Hawaiian Islands, is much larger than previously thought. « We were surprised to find such a large feature under the Marquesas Islands that we didn’t even know existed before, » says an associate professor of geology at UMD and co-author of the study.

It’s really exciting, because it shows how the Sequencer algorithm can help us contextualize seismogram data around the world in a way that we couldn’t do before. The researchers said their discovery could probably lead to a better understanding of the processes that have taken place over the years that have contributed to the evolution of the planet over time.