Mysterious fluctuations discovered 2,900km underground

An international team of scientists has just recorded a huge geological anomaly: a mysterious change occurring at a depth of nearly 2,900km, right at the boundary between the Earth's mantle and core.

The GRACE satellites, which flew in succession from 2002 to 2017, detected changes in Earth's gravity - Photo: NASA

The study, published in Geophysical Research Letters, shows that rock structures in the deepest part of the mantle can change dynamically on short timescales. The findings could have important implications for understanding how large earthquakes form or how the magnetic field, the "shield" that protects life on Earth, is created.

The research team, led by scientist Charlotte Gaugne Gouranton (Université de Paris), with the prominent participation of geophysicist Isabelle Panet (Université Gustave Eiffel, France), exploited data from the GRACE satellite mission (2002 - 2017), a US-German cooperation project designed to measure the Earth's gravitational field.

The two GRACE satellites fly in tandem at a fixed distance, making them exceptionally precise instruments. When the lead satellite passes over a large mass, such as a mountain range or aquifer, its stronger gravitational pull causes it to shift slightly, changing its distance from the trailing satellite. These millimeter-scale changes accurately reflect changes in gravity.

GRACE was initially intended primarily for studying the water cycle: melting ice, groundwater levels. But thanks to its extreme sensitivity, the team realized it could also "catch" fluctuations deep underground, and they had previously used this data to detect signs at depths of hundreds of kilometers, related to large earthquakes.

In the new analysis, an unusual signal appeared, most clearly in 2007, centered under the Atlantic Ocean, off the coast of Africa. The nature of this signal completely ruled out the possibility of it being caused by shifting water or ice on the surface. “At least part of the cause must come from inside the solid Earth, from very deep,” Dr. Panet emphasized.

Notably, at the same time in 2007, satellites that monitor magnetic fields also recorded a geomagnetic anomaly in the same area. The coincidence in space and time suggests that the two phenomena, gravity and magnetism, may be two aspects of the same deep geological process.

The team hypothesizes that at the base of the mantle, where rocks rich in perovskite minerals are found, a change occurs at the atomic level. Under enormous pressure, the mineral's crystal structure may "collapse" into a denser form, a process known as a phase transition.

This change densifies the rock, causing the area to increase in mass, creating a gravity signal. Nearby rocks are forced to rearrange, causing the boundary between the mantle and core to warp by about 10cm. That may sound small, but the change is enough to affect the convection currents of molten iron in the outer core, which are the source of Earth’s magnetic field and caused the geomagnetic disturbance in 2007.

Dr Panet cautioned that this scenario would need further testing: "This is just a hypothesis, we still need more evidence." However, the mere observation of such an event would be considered a major step forward in Earth science.

"For the first time we have compelling evidence that dynamic processes at the base of the mantle are happening fast enough to be studied as they happen," said Professor Barbara Romanowicz, a seismologist at the University of California, Berkeley.

So far, the team has not detected any similar gravity signals since 2007. But monitoring continues. Data from the next generation of GRACE satellites is expected to help reveal more mysteries at the deepest levels of the planet, where the Earth quietly "breathes" and moves.

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Source: https://tuoitre.vn/phat-hien-bien-dong-bi-an-sau-2-900km-duoi-long-dat-20250918183852224.htm