Advanced analysis of over two million seismic records using artificial intelligence has revealed six previously unknown geological structures near the boundary where Earth’s rocky mantle meets its liquid outer core, nearly 2,900 kilometers below the surface, according to research published in the Journal of Geophysical Research: Solid Earth.
Unlocking Decades of Seismic Data With Artificial Intelligence
To explore the interior of the Earth without drilling—a feat that remains technically impossible at such depths—geophysical researchers rely on natural events. Every large-magnitude earthquake emits seismic waves that travel through the planet and bounce off different rock densities and structures. In a recent study, researchers processed more than two million precursor PKP waves recorded between 1990 and 2024 from earthquakes with magnitudes exceeding 6.0.
By applying artificial intelligence algorithms to three decades of global seismic data, the team identified six distinct, uncatalogued structures sitting right at the frontier between the mantle and the core. Understanding this boundary is critical for geophysicists because it governs the heat exchange that drives mantle convection, plate tectonics, and the internal dynamo sustaining Earth’s magnetic field.
The Physics of Earth’s Deepest Layers and Historic Discoveries
The Earth’s crust is a very thin layer compared to the planet’s mantle and core. What is the Earth’s mantle? The Earth’s crust is formed by more or less rigid plates that rest or float on a high-temperature viscous material called the mantle. Sometimes, these materials reach the surface through erupting volcanoes. Additionally, they flow continuously through cracks in the mid-ocean ridges to form new crust. At a depth of about 3,000 km is the Earth’s core, an area where metals predominate and which, far from being indifferent to us, influences life on the planet, as it is considered responsible for most of the magnetic and electrical phenomena that characterize our planet. The Earth has a magnetic field around it thanks to its core, and that protects us from harmful solar radiation. The heaviest materials of our planet are located in the Earth’s mantle and core and constitute most of its mass. The Earth’s mantle: The Earth’s mantle is a layer about 2,900 km thick, consisting of denser rocks where silicates predominate. At a depth of about 650-670 km, a special acceleration of seismic waves occurs, which has allowed for the definition of a boundary between the upper and lower mantle. This phenomenon is due to a change in structure, moving from a plastic medium to a rigid one, where it is possible that the general chemical composition of the entire area is preserved. The continental crust grew through a chemical differentiation of the upper mantle that began about 3.8 billion years ago. At the base of the upper mantle, the density is about 5.5 grams per cubic centimeter. In the upper zone of the Earth’s mantle, convection currents occur, similar to water boiling in a pot, moving from the hotter lower portion to the colder upper portion. These currents are the engine that moves the lithospheric plates. The Earth’s core: The terrestrial core is a gigantic metallic sphere with a radius of 3,485 km, meaning a size similar to the planet Mars. The density varies from nearly 9 grams per cubic centimeter at the outer edge to 12 in the internal part. The Earth’s core is mainly composed of iron and nickel, with additions of copper, oxygen, and sulfur. > The outer core is liquid, with a radius of 2,300 km. The difference with the inner core is manifested by a sharp increase in the speed of “P” seismic waves at a depth between 5,000 and 5,200 km. The inner core has a radius of 1,220 km. It is believed to be solid and has a temperature between 4,000 and 5,000 °C. It is possible that the inner core is the result of the crystallization of what was a larger liquid mass and that this growth process continues. The heat energy of the core influences the mant
Deep Mantle Earthquakes Challenging Geological Models
Beyond structural anomalies at the core-mantle boundary, recent historical analysis highlights unexpected seismic behavior originating deep within the mantle itself. In 1979, a team of researchers detected an unusual earthquake in northern Utah that originated at a depth of about 90 kilometers. At that time, the finding drew attention because that area of the Earth’s interior was considered too deep for rocks to break suddenly, since, according to the geological models of the time, they should deform in a slow and continuous manner.
The phenomenon occurred during the early hours of February 24, 1979, when seismological equipment detected movement under the city of Randolph, located near the Utah border with the states of Idaho and Wyoming. Although the instruments recorded a magnitude 3.8 quake, no resident reported feeling it, sparking the interest of the scientific community. Faced with these anomalies, George Zandt, who was at the time a postdoctoral researcher at the University of Utah, examined the seismic records in detail.
“The great depth explained why people on the surface did not feel it. I performed other analyses that convinced me of the reality of the great depth, but it was difficult to convince others that an anomalous earthquake occurred in the Earth’s mantle, in a region where they should not exist”, Zandt noted.
Decades after the unusual quake recorded in 1979, a group of researchers from the University of Utah re-examined the original seismic records along with other events that presented similar characteristics. The study, led by Geology professor Keith Koper, confirmed the existence of nine earthquakes that originated at great depth in northern Utah and southwestern Wyoming.
