Scientists spot 'hot, dense structures' hiding near Earth's core

Katie Ramirez
June 14, 2020

Geophysicists from the University of Maryland studied data from thousands of recorded seismic waves and sound waves traveling through our planet, to search for echoes from the boundary between Earth's molten core and the solid mantle layer above it.

This map shows a large area under the Pacific and reveals hot and dense regions below Hawaii and the Marquesas Islands in French Polynesia.

The analysts took care of it 30 years of information - around 7,000 seismograms of one specific sort of seismic wave - searching for the seismic echoes showing a ultra-low speed zone that we may have missed in past examinations. Measuring the time and amplitude of these echoes can reveal subsurface physical properties and reveal structures, but research has largely been limited and only able to illustrate this landscape in a "piecemeal way".

"By looking at thousands of core-mantle boundary echoes at once, instead of focusing on a few at a time, as is usually done, we have gotten a totally new perspective", said Doyeon Kim, the lead author of the study from UMD's Department of Geology. This process is similar to the way bats echolocate to map their environment. Pictured, earthquakes (white lines) travel through the Earth from quake sites (orange) to seismographs (blue).

"With this new way to look at the data globally, we were able to see weak signals much more clearly", said Brice Menard, astrophysicist at Johns Hopkins University and one of the team members.

The researchers were shocked by the discovery of the three-dimensional structures near the core-mantle boundary scattering almost half of the diffracted waves.

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This discovery comes after researchers from the University of Maryland in the U.S. analyzed data from 7000 recorded earthquakes, including major earthquakes, recorded in the Pacific Ocean region between 1990 and 2018.

To compensate for the issue, researchers affiliated with the University of Maryland, Tel Aviv University and John Hopkins University made a decision to turn to a most peculiar source. A comprehensive view of the deep Earth below the Pacific region was provided by the diffracted waves along the core-mantle boundary.

The scientists analyzed echoes of seismic waves traveling beneath the Pacific Ocean basin. When applied to seismograms from earthquakes, the algorithm discovered a large number of shear wave echoes. "That was surprising because we were expecting them to be more rare, and what that means is the anomalous structures at the core-mantle boundary are much more widespread than previously thought". It is known as the Sequencer, and it was originally created to run through very large astronomical datasets to look for repeating patterns.

"We were surprised to find such a big feature beneath the Marquesas Islands that we didn't even know existed before", Lekic said.

The team from Baltimore in the USA used an algorithm known as "the Sequencer" which can find trends in large-scale datasets - such as used by astronomers.

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