Ancient Slab Beneath U.S. Heartland Linked to Crustal Thinning Across the Region
A massive underground structure deep beneath the central United States is quietly reshaping the continent from below. Scientists have discovered that a buried remnant of ancient crust is dragging surface materials downward, drawing rock from a wide area into a funnel-like zone beneath the Midwest. This movement is believed to be causing parts of Earth’s crust in the region to thin significantly—a phenomenon that surprisingly stretches beyond the immediate area affected.
At the heart of the discovery is the Farallon slab, a long-subducted tectonic plate that now rests roughly 660 kilometers below the surface. Published in Nature Geoscience, the new study connects this ancient remnant to what geologists call “cratonic thinning.” Cratons are some of the oldest and most stable parts of Earth’s crust, typically untouched by tectonic shifts. But the presence of the Farallon slab seems to be disturbing this stability, pulling at the base of the continent and causing unexpected changes to the deep structure of North America.
The research was led by Junlin Hua, who conducted the seismic mapping as a postdoctoral researcher at The University of Texas at Austin. Now a professor in China, Hua described the widespread crustal thinning as an eye-opening find. According to him, the study presents a novel explanation for long-observed changes beneath the region. It’s a departure from conventional thinking, and the research team believes it provides a clearer view of how deep-Earth processes can influence surface geology over vast distances.
To explore these hidden movements, scientists relied on a powerful seismic imaging technique called full-waveform inversion. This method allowed researchers to capture detailed 3D images of Earth’s interior, offering an unprecedented look at the interaction between the lower mantle and the overlying lithosphere. Thorsten Becker, chair of geophysics at UT Austin, noted that the imaging revealed a distinctive “dripping” pattern in the lithosphere—only present when the Farallon slab was included in computer models. When the slab was removed from simulations, the phenomenon vanished, reinforcing its role in reshaping the continent from below.