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Seismic waves show changes occurring in the Earth’s outer core

– Rost9/

Analysis of seismic waves from two separate earthquakes, which occurred in the same region of the globe but were separated by 20 years, revealed changes in the composition of the Earth’s outer core.

“The fact that it is moving faster indicates a new, lighter material.”

Today, most of our knowledge about the bowels of the Earth comes from studying waves generated by earthquakes. The latter may indicate in particular The nature of the rocks and minerals that make up them. A vortex layer of liquid iron and nickel separates the mantle from the inner core, The outer core directly affects our planet’s magnetic field, which protects us from deadly cosmic radiation. This is why understanding it and monitoring its development is essential.

In the context of the work published in the magazine Nature Communications Earth and Environmentresearchers from the University of Virginia studied seismic data related to two earthquakes, which occurred near the Kermadec Islands (South Pacific) between May 1997 and September 2018. It turned out thatA certain type of wave took one second less to propagate through an area of ​​the outer core More than two decades ago. which Leeds to Changes in the composition of the latter.

SKS waves pass through the mantle as shear waves (S), then enter the outer core as pressure waves (K), before exiting the other side and crossing the mantle again as shear wave Ying Zhou, lead author of the study, explains. ” The fact that they are moving faster indicates the existence of a new, lighter material. »

Land area
– Dima Zell /

An insight into the convection of the Earth’s outer core

It occurs in liquid iron from the outer core where it crystallizes upon contact with the inner core pregnancy It causes electric currents to form and flow, controlling the magnetic field around us. However, the relationship between the latter and the outer core is still not well understood (it depends largely on hypothetical modelling).

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If you look at the geomagnetic North Pole, it is currently moving at a rate of about 50 kilometers per year, away from Canada and closer to Siberia Chu says. ” The fact that the magnetic field changes daily indicates that convection also changes over time, but there is no direct evidence. we never saw her. »

Although the differences observed here are very small, it presents Insight into the development of the outer core. The study authors believe that lighter elements such as hydrogen, carbon and oxygen have been released there since 1997, implying About 2 to 3% density loss And the The velocity of convective flow is about 40 kilometers per hour.