Researchers collect seismic wave data in Antarctica. (Photo: Edward Garnero & Mingming Li).
Using seismic data collected in Antarctica over the past three years, a team concludes that millions of years ago, the ocean floor moved toward the center of the Earth and stopped as a relatively thin layer around the core. planet. The findings could affect our understanding of how heat escapes from the core, or how matter in the ocean can return to the surface through volcanic eruptions, the researchers say. They published the results of the study April 5 in the journal Science Advances .
When geoscientist Samantha Hansen and colleagues from the University of Alabama (UA) installed 15 seismometers in Antarctica in 2012, they wanted to use waves from earthquakes around the planet to take pictures of buried mountains. mostly underneath the ice. While that three-year study was very successful and produced several papers, the data revealed unusual energy that emerges after waves from earthquakes pass through the boundary between the core and mantle (CMB ) . This prompted Hansen and colleagues to conduct further research.
The CMB lies at a depth of about 3,219km below the Earth’s surface. There, the team found that seismic waves slowed down when they hit a certain layer. Although the new layer is about 5-40 km deep, it is relatively thin in terms of planetary composition. The slowing down of the traveling wave causes the region to be named the ultra-low velocity region (ULVZ) .
Analyzing thousands of seismic records from Antarctica , the team ‘s high – resolution imaging method detected unusually thin regions of matter in the CMB at every probe site . According to Edward Garnero, a professor in the School of Space Science and Exploration at the University of Arizona, the thickness of the material varies from a few kilometers to tens of kilometers, indicating that they are seeing mountains at the core, some of which are high. 5 times higher than Mount Everest.
The way the seismic wave slows down as it hits the ULVZ led the team to conclude it consisted of material from an ancient ocean floor that was pushed through the Earth’s mantle over hundreds of millions of years. That’s because such matter is even denser than the liquid rock that composes the mantle, slowing the speed of seismic waves to levels shown in the data.
Data from the study indicate that the ULVZ could encircle the entire core of the Earth. “Seismological studies like ours provide the highest-resolution snapshot of the inner structure of the planet, and we found that this structure is much more complex than previously thought. The study provides a relevant link. between the shallow and deep structure of the Earth and the processes of planetary motion”.
