Scientists have investigated a series of unusual, deep earthquakes occurring beneath northern Utah, identifying them as distinct events originating in the Earth’s upper mantle rather than the crust.
Anomalous Seismic Activity
The phenomenon was first noted in 1979 with a magnitude 3.8 tremor recorded at a depth of over 55 miles below sea level. This depth was far greater than conventional geological models at the time believed possible for seismic activity. George Zandt, a former University of Utah seismology researcher who helped record the initial event, stated that while he was convinced of the deep origin, convincing others of this anomalous mantle earthquake was challenging.
Now, a new study published in The Seismic Record, led by University of Utah geology professor Keith Koper and Zandt, has analyzed eight subsequent deep earthquakes in the region. The findings confirm these tremors occur within the Earth’s upper mantle, significantly below the crust-mantle boundary.
Archetypal Continental Mantle Events
Koper and his colleagues have classified these events as “archetypal continental mantle events.” This classification suggests they are related to movements within the Earth’s mantle that occur over extremely long geological timescales. The research underscores the vast unknowns surrounding deep tectonic dynamics and how they differ from more familiar, shallow crust-based earthquakes.
“It’s sort of a mystery in terms of fundamental physics,” Koper commented, questioning the mechanisms that allow these deep events to occur. He also highlighted the uncertainty regarding their potential size, contrasting it with the more predictable maximum magnitudes of crustal earthquakes, which can be estimated by mapping surface faults.
Wyoming Craton Interaction
Unlike shallow earthquakes, these deep events do not typically exhibit foreshocks or aftershocks. The research team has located their occurrence at the western edge of the Wyoming Craton, a stable, ancient block of the Earth’s lithosphere that extends across northern Utah and southwest Wyoming. Temperatures in this region can surpass 1,300 degrees Fahrenheit.
The prevailing hypothesis is that these deep earthquakes are triggered by the slow squeezing of the mantle by the Wyoming Craton. Koper explained that over millions of years, the mantle interacts with and flows around this rigid cratonic structure. This interaction, where mantle flow is diverted around the “hard cratonic root,” leads to increased strain rates and deformation, generating additional stresses that can cause seismic events.
“We think it’s that interaction between the keel of the iceberg and the medium around it that’s leading to these earthquakes,” Koper added, likening the craton’s base to an iceberg’s keel.
Norman Pearlstine is the Chief Editor of News Raise and focuses on Business news. His responsibility is to oversee the editorial content including business, commodities, personal investments and the stock market.
