Seismologists have identified a series of “deep earthquakes” occurring in the Earth’s upper mantle beneath northern Utah, challenging long-held geological assumptions about how and where seismic activity can originate. University of Utah researchers, led by professor Keith Koper and seismologist George Zandt, confirmed in a study published in The Seismic Record that these tremors occur dozens of miles below the crust, far deeper than conventional models previously suggested was possible for this region.
Why do deep earthquakes defy conventional geology?
Standard geological models categorize earthquakes as crustal events, typically occurring at much shallower depths where the Earth’s plates are brittle. According to Koper, these deep-mantle tremors present a fundamental physics mystery because they occur in regions where high temperatures—often exceeding 1,300 degrees Fahrenheit—should theoretically prevent the buildup of stress required for a rupture. Unlike shallow earthquakes, these deep events do not produce the typical patterns of foreshocks or aftershocks, making them difficult to detect and monitor using traditional seismic arrays.
Unlike common earthquakes that occur within the Earth’s rigid outer crust, these deep-mantle tremors originate in the upper mantle, where the extreme heat and pressure typically cause rock to flow like plastic rather than snap like brittle glass.
What is the Wyoming Craton’s role in seismic activity?
The research team identified the western edge of the Wyoming Craton as the primary location for these anomalous events. The Wyoming Craton is a massive, rigid block of the Earth’s lithosphere. According to Koper, the mantle is slowly flowing around this “keel,” similar to how water flows around the submerged portion of an iceberg. This interaction creates localized strain and deformation, forcing the mantle to rupture despite the extreme environmental conditions that would usually mitigate such stress.
Are these deep earthquakes dangerous?
The primary concern for geologists is the unknown potential for the magnitude of these deep events. Koper noted that while crustal earthquakes can be mapped by measuring surface faults, researchers currently lack the data to determine the maximum possible size of a mantle-based earthquake. Because these quakes do not provide early warning signs like smaller foreshocks, they remain a significant variable in regional seismic risk assessments. The study analyzed eight specific events, confirming that these are not isolated anomalies but part of a persistent tectonic process.
Comparison: Crustal vs. Deep Mantle Earthquakes
| Feature | Crustal Earthquakes | Deep Mantle Earthquakes |
|---|---|---|
| Depth | Near the surface | 55+ miles deep |
| Warning Signs | Foreshocks/Aftershocks | None |
| Predictability | Mapped via surface faults | Unknown maximum size |
Frequently Asked Questions
How deep are these “deep” earthquakes?
Recorded data from the 1979 event and subsequent studies show these tremors occur more than 55 miles below sea level, well within the Earth’s upper mantle.
Can we predict when the next deep earthquake will happen?
No. According to Koper, these quakes do not announce themselves with foreshocks, and current technology cannot map the internal mantle flow with the same precision used for surface faults.
Is this phenomenon unique to Utah?
The study focuses on the interaction between the mantle and the Wyoming Craton in Utah and Wyoming, but the underlying mechanics of mantle flow around rigid lithospheric blocks are a subject of ongoing global geophysical research.
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