Updated

Updated · SciTechDaily · Jun 12

Utah Seismologists Confirm 9 Mantle Earthquakes Beneath Utah as 4.1 Quake Strengthens Case

Updated

Updated · SciTechDaily · Jun 12

Utah Seismologists Confirm 9 Mantle Earthquakes Beneath Utah as 4.1 Quake Strengthens Case

Q: Scientists just confirmed 'impossible' earthquakes deep in the mantle. How powerful could these mysterious tremors actually become?

Scientists do not yet know how powerful these deep mantle earthquakes can become. So far, the confirmed Continental Mantle Earthquakes beneath Utah and Wyoming have been modest: a magnitude 3.8 event near Randolph in 1979 and a magnitude 4.1 quake near Maeser in 2025. Those are the clearest documented examples, and both originated far below the crust, at roughly 90 kilometers and 68 kilometers deep. What makes them unusual is not their size so far, but where they happen. At those depths, rocks are expected to deform slowly under extreme heat and pressure rather than break suddenly. That means scientists lack the usual tools used to estimate an earthquake’s upper limit. In crustal earthquakes, researchers can often map faults at or near the surface and use their length to infer how large a rupture could get. For these mantle events, there are no visible surface faults and no established magnitude ceiling. Keith Koper’s team has been explicit on that point: there is currently no reliable way to say how big these tremors might ultimately become. The events also appear to occur in isolation, without the foreshocks or aftershocks commonly seen in shallower quakes, which further limits forecasting. The best evidence today is that these are real but rare upper-mantle earthquakes concentrated near the edge of the Wyoming Craton. Their confirmed magnitudes are small to moderate, but their maximum possible strength remains an open scientific question.

3 articles · Updated · SciTechDaily · Jun 12

Nine earthquakes beneath northern Utah and southwestern Wyoming were confirmed to have originated in the upper mantle, validating a 1979 magnitude 3.8 event once considered nearly impossible beneath a continent.
A magnitude 4.1 quake near Maeser on Sept. 10, 2025, provided the clearest recent evidence: researchers placed it 68 kilometers deep, more than 20 kilometers below the crust-mantle boundary.
University of Utah scientists reanalyzed decades of archived seismic records and wave-arrival times, with graduate student Sean Hutchings identifying several events previously classified as shallower crustal earthquakes.
The quakes cluster near the western edge of the Wyoming Craton, where researchers say mantle flow diverted around the ancient lithospheric root raises strain and stress enough to trigger these rare events.
The finding challenges standard expectations that hot, high-pressure mantle rock should deform slowly rather than rupture, and leaves scientists uncertain how large such isolated quakes can become.

Sources

SciTechDaily3d ago

University of Utah Seismologists Confirm Rare Deep Continental Mantle Earthquakes Beneath Utah

MSN3d ago

Scientists investigate strange rumbling beneath Utah

Yahoo! Voices3d ago

Scientists Investigate Strange Rumbling Beneath Utah

Scientists just confirmed 'impossible' earthquakes deep in the mantle. How powerful could these mysterious tremors actually become?

If Earth's mantle flows like taffy, how can it suddenly fracture? What is the secret behind these deep 'impossible' earthquakes?

The 2025 Maeser Quake and the Mystery of Continental Mantle Earthquakes: Implications for Seismic Risk

Overview

On September 10, 2025, the Maeser earthquake struck Northeastern Utah with a magnitude of 4.1, marking a breakthrough in seismology as it was identified as an 'Archetypal Continental Mantle Event.' This rare deep earthquake, confirmed by research published in The Seismic Record and Geophysical Research Letters, became a key example for understanding seismic activity within the Earth's upper mantle. The University of Utah Seismograph Stations also found four other suspected mantle earthquakes in 2025, highlighting the importance of studying and confirming these deep events to advance knowledge of Earth's interior dynamics.

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