When a powerful earthquake strikes, it shakes the ground for just a few seconds. But the Earth doesn’t stop moving. For hours afterward, it continues to vibrate at frequencies that we can’t hear. Seismometers around the world pick up these vibrations, revealing secrets about what lies beneath us.
Scientists have noticed that seismic waves travel differently in some parts of the Earth, particularly beneath Africa and the central Pacific. These waves slow down, hinting at something unusual buried 2,900 kilometers deep.
Researchers from Utrecht University in the Netherlands have been studying these unusual signals from the biggest earthquakes. They focused on how much energy the waves lose as they travel—this loss, called “attenuation,” can reveal a lot about what’s going on underground. By looking at the Earth as a whole system, they created a model to understand what’s happening at the boundary between the Earth’s core and mantle.
Their findings unveiled two enormous structures, known as Large Low Shear Velocity Provinces (LLSVPs). Each one towers about 1,000 kilometers high—almost 100 times the height of Mount Everest. They’re situated under Africa and the Pacific Ocean, stretching as wide as 5,000 kilometers. This makes them some of the largest known features deep inside the Earth.
Instead of just looking at how quickly the waves move, the researchers used a method called normal-mode seismology. This technique analyzes how the Earth oscillates after a quake. Their comprehensive study has led to a new 3D model called QS4L3, which offers sharper insights into the mantle’s composition.
Sujania Talavera-Soza, the lead author of the study, explained how they distinguished between different effects in the mantle—something earlier studies couldn’t do reliably. They noted that the LLSVPs, while not mountains in the traditional sense, are significant thermochemical structures that influence how the mantle flows.
The results showed an intriguing pattern. In the upper mantle, areas of high attenuation linked to hot rock. But in the lower mantle, this pattern flipped. The LLSVPs had low attenuation, suggesting they’re made of different materials and larger mineral grains than the surrounding rock.
Researchers believe these structures formed from ancient oceanic crust that sank into the mantle billions of years ago. They’re chemically unique, resisting mixing with the rest of the mantle. “They seem to be remnants from the early days of the Earth,” the authors note.
This groundbreaking study enhances our understanding of the inner Earth. The LLSVPs are massive anchors, influencing the movement of tectonic plates on the surface and contributing to volcanic activity in places like Hawaii and Iceland.
What’s most astonishing is that these giants lie hidden deep below us—no one will ever see them in person, yet their influence resonates with every quake that shakes our planet. The tallest mountains on Earth aren’t just on land or at sea; they’re buried far beneath us, playing a vital role in our planet’s dynamics.
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