Scientists confirm 'impossible' earthquakes deep in Earth's mantle beneath Utah
University of Utah researchers confirmed nine earthquakes beneath northern Utah and southwestern Wyoming that began far below the crust, in mantle rock long thought too hot to break. A 1979 quake started about 90 kilometers down; the newest, in September 2025, was about 68 kilome
University of Utah geology professor Keith Koper's team reexamined waveform data from a 1979 magnitude 3.8 quake beneath Randolph, Utah, plus eight other suspected deep quakes in northern Utah and southwestern Wyoming. All nine began well below the crust, confirming a rare class of continental mantle earthquakes. The newest struck September 2025 near Maeser in Utah's Uinta Basin: magnitude 4.1, roughly 68 kilometers deep. Findings published in The Seismic Record and Geophysical Research Letters raise new questions about seismic hazard in the region.