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Deep Quakes: Utah's Mystery Shakes Unveiled
30 May
Summary
- Newly identified mantle earthquakes occur deep underground.
- These deep quakes are often unfelt due to their depth.
- Scientists are still studying these unique seismic events.
A mysterious earthquake that occurred in Randolph, Utah, in February 1979, has led geologists to identify a new category of seismic activity: mantle earthquakes. These deep quakes originate as deep as 43 to 55 miles underground, beneath Earth's tectonic plates, explaining why the magnitude 3.8 event in 1979 went unnoticed by the town's 467 residents.
Researchers now understand that such deep seismic events, unlike typical earthquakes originating closer to the surface, often lack the intensity to be felt. Geophysicist Keith Koper has led efforts to catalogue these mantle quakes, confirming nine such instances that occurred without aftershocks and originated near the ancient Wyoming Craton.
A recent magnitude 4.1 mantle earthquake in Utah's Uinta Basin on September 10, 2025, occurred at a depth of 42 miles. Scientists describe the material at this depth as behaving like "taffy" on long timescales due to high temperatures and pressures. Despite their low surface intensity, understanding these deep, potentially powerful events is crucial for assessing seismic hazards.
