When a powerful earthquake occurs, the Earth literally “rings”—seismic waves propagate across the globe. For seismologists, this is an opportunity to peer into the depths: by tracking how the waves speed up, slow down, and reflect in different layers, they obtain something akin to an X-ray of the planet. Now, an international team of researchers, having analyzed about 5300 major quakes since 1995, has constructed the most detailed map yet of the mantle-core boundary—the layer at a depth of approximately 2900 km.
The findings revealed that ancient tectonic plates, which once plunged into the interior (subducted) hundreds of millions of years ago, have not dissipated without a trace. They accumulate on the surface of the outer core, forming gigantic “plate graveyards,” and then sort of spread sideways along the core-mantle border, initiating slow but substantial flows of rock there. A significant portion of the recorded seismic anisotropy—the directional passage of waves—is precisely connected to these zones of residual plates.
The core-mantle boundary, contrary to simplified textbook diagrams, is far from smooth. Previously, colossal hot structures were discovered there—large regions with low shear velocity, hundreds of kilometers high, and surrounding them, “mountain ranges” of chaotically piled plate fragments. The new study clarified: a substantial part of the lower mantle is permeated by a complex flow system formed precisely by these sunken plates.
The authors worked with a network of seismometers worldwide, gathering subtle variations in the speed of waves circling the core. In some sections of the lower mantle, data density increased by 100 times compared to prior models. This allowed for the first correlation of global geodynamic models with observable structure: how ancient plates sink and spread along the core directly influences mantle convection, plate tectonics, and ultimately, volcanism and the movement of continents beneath our feet, reports planet-today.ru.
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