Based on a new method of analyzing seismic data, this research reveals that the imposing blocks of dense matter located at the limit between the nucleus and the mantle of the planet are much more widespread than scientists previously estimated. .
An algorithm dedicated to the study of stars to probe the bowels of the Earth
The limit of earth core located some 2,900 kilometers below the surface of the Earth, scientists are forced to be creative in order to probe the bowels of our planet. By studying the way in which earthquakes and earthquakes propagate through different types of materials, seismologists were able to establish a global map of its structure, revealing the presence of imposing blocks of hot materials, which can be the size of a continent, on the border between the nucleus and the earthly mantle.
The heat causing higher degrees of fusion, these zones have the effect of slowing the speed of propagation of seismic waves towards the Earth’s nucleus, they are therefore known as ” ultra low speed zones ” Although the nature of these structures is still unknown (it could be magma or molten iron escaping from the nucleus), better knowledge of their location would allow scientists to better understand the geological processes involved in such depths.
However, the classic approach to studying earthquakes only provides snippets of information: each earthquake probes only a narrow area, and the weakest signals can get lost in the wider noise. In order to get around this problem, an international team of researchers, whose work was presented in the journal Science, relied on the Sequencing, an algorithm designed for the study of stars and capable of traversing large sets of astronomical data in order to identify scientific models.
After having modified it, the researchers fed it with nearly three decades of seismic data, that is to say approximately 7000 seismograms of a particular type of wave, in order to identify seismic echoes indicating the presence of zones of ultra speed bass that might not have been detected by previous searches.
” By examining thousands of echoes at the boundary between the nucleus and the mantle simultaneously, rather than focusing on a few at the same time, as we usually do, we have obtained a completely new perspective. “Says the geologist Doyeon Kim of the’university of maryland. ” This analysis showed that the region located at the limit between the nucleus and the Earth’s mantle shelters many structures which can produce these echoes, something that we had not realized before because we had only a limited vision.. “
The results returned by the algorithm revealed subtle changes in the seismic waveforms from earthquakes in Asia and in Oceania, suggesting an ultra low speed zone under the Marquesas Islands, in the South Pacific, having never been identified before.
” We were surprised to discover such an important structure under the Marquesas Islands, the existence of which we had previously ignored “, Underlines the geologist Vedran Lekić of the’university of maryland. ” It’s really exciting, because it shows how the Sequencer algorithm can help us contextualize seismogram data around the world better than we could have done before.. “
“We expected them to be much rarer”
It also turned out that the ultra low speed zone previously identified under Hawaii produced much more intense seismic echoes than scientists previously estimated. This suggests that the latter is much more extensive than what previous studies had estimated. More generally, this new research suggests that these structures are much more widespread than previously thought.
” We have identified this type of echo for around 40% of all seismic wave paths “, Advance Lekić. ” Which turned out to be surprising, since we expected them to be much rarer. “
Having demonstrated the effectiveness of the algorithm for this type of wave, the team’s approach will now be able to be applied to other types of waves and frequencies. This could make it possible to draw up a new high-resolution map of the bowels of the Earth. In return, the physical properties thus revealed could help geologists to deduce the chemistry and temperature of these structures, and thus determine the causes of their presence.