A team of researchers from the University of Maryland (USA) have discovered using state-of-the-art imaging techniques a series of huge and unexpected structures near the core of the Earth, deep in the Pacific Ocean between the core and the mantle of the earth; a new reminder of how little we know about the interior of the planet where we live.
What these highly heterogeneous structures might be is still unknown – maybe it could be magma, molten iron leaks from the core, or something else, but with a more complete and detailed map of where they are, scientists will be able to better understand the geological processes behind them. occur indoors.
“The anomalous structures in the boundary between the core and the mantle are much more widespread than previously thought,” explains Vedran Lekić, associate professor of geology at the University of Maryland, co-author of the work published in the journal Science .
The experts used a machine learning algorithm called Sequencer to analyze the seismic of hundreds of earthquakes, collected over decades, to map the Earth’s interior in unprecedented detail, a process they compared to how bats use echolocation to map your environment.
Regarding the core, the central limit is about 2,900 kilometers below the surface of the Earth, so to know what the conditions are like at such a distance we have to be creative. Hence the use of earthquake tools.
When an earthquake occurs, it produces seismic waves below the Earth’s surface capable of traveling thousands of kilometers. As these waves encounter changes in the temperature, composition, or density of rocks, their velocity can change, bend, or disperse in ways that create echoes that can be detected by strategically located seismographs at locations around the world. Measuring the time and amplitude of these echoes can reveal the physical properties of the subsurface and reveal structures. But this study went further.
They analyzed thousands of seismic wave recordings as they traveled beneath the Pacific Ocean basin by looking at a specific type of wave called a shear wave, named for its “s” shape. The algorithm then analyzed 7,000 seismograms from hundreds of earthquakes with a magnitude of 6.5 or greater around the Pacific Ocean basin between 1990 and 2018 in order to systematically detect seismic echoes .
Their analysis revealed a previously unknown structure under the volcanic Marquesas Islands in the South Pacific and showed that the structure under the Hawaiian Islands is much larger than previously known.
“By observing thousands of echoes from the central mantle boundary at the same time, instead of focusing on a few at a time, as is often the case, we have gained an entirely new perspective,” said Doyeon Kim of the Department of Geology at the University of Maryland.
“This 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 only had a narrow view .”
According to the findings, the mysterious structure is composed of a vast area of unusually dense and hot rock at the boundary between the core and the mantle below Hawaii.
“We found echoes in about 40% of all seismic wave paths, ” said Vedran Lekik, also a co-author of the study. “That was surprising because we expected them to be rarer, and what that means is that the anomalous structures at the core-mantle boundary are much more widespread than previously thought.”
We continue to discover more data on how plate tectonics has shaped our planet over millions of years. Furthermore, thanks to this new method, scientists will be able to apply it to other types of waves and frequencies, which will facilitate a new high-resolution map of the interior of the Earth.
Referencia: D. Kim, V. Lekić, B. Ménard, D. Baron and M. Taghizadeh-Popp. Sequencing Seismograms: A Panoptic View of Scattering in the Core-Mantle Boundary Region. Science, 2020 DOI: 10.1126/science.aba8972
