University of Utah Confirms 9 Continental Mantle Earthquakes, Including 1979 Randolph Quake at 90 Kilometers
Updated
Updated · Earth.com · May 29
University of Utah Confirms 9 Continental Mantle Earthquakes, Including 1979 Randolph Quake at 90 Kilometers
3 articles · Updated · Earth.com · May 29
Nine earthquakes beneath northern Utah and southwest Wyoming were confirmed to have originated 70 to 90 kilometers deep in the upper mantle, validating the long-disputed 1979 magnitude 3.8 Randolph event.
Waveform reanalysis by Keith Koper's team and graduate student Sean Hutchings showed several quakes had been misclassified as crustal events; a magnitude 4.1 shock near Maeser in September 2025 was one of the newly confirmed mantle quakes.
These continental mantle earthquakes occur alone—without foreshocks or aftershocks—and cluster near the western edge of the Wyoming Craton, where temperatures can exceed 700C.
Researchers say mantle flow diverted around the craton's rigid root builds strain and stress deep below the Moho, offering a mechanism for quakes in rock that should deform like slow-moving taffy.
The finding complicates hazard estimates because these quakes leave no surface faults to map, and researchers still do not know how large such mantle events can become.
Scientists proved quakes happen in the 'unbreakable' mantle. What long-held geology rule will be the next to fall?
With mantle earthquakes now confirmed, how must we reassess seismic risk for supposedly stable continental regions?
Earth's mantle can host earthquakes. Could deep 'marsquakes' be the key to unlocking the Red Planet's geological secrets?