Topic: Earth Science

A team of scientists from the University of Utah confirmed that a deep earthquake occurred in 1979. The earthquake was unusual because it happened at a depth of about 90 kilometers, which is much deeper than usual.

The event seemed to originate far deeper than earthquakes were thought capable of occurring beneath a continent.

In the early morning of February 24, 1979, a small earthquake struck beneath the town of Randolph near Utah's borders with Idaho and Wyoming. Although it registered a magnitude of 3.8, nobody reported feeling it. The seismic recordings also appeared unusual, prompting closer examination.

At the time, University of Utah postdoctoral researcher George Zandt analyzed the data and calculated that the earthquake originated about 90 kilometers below sea level. That depth placed it well below Earth's crust and deep within the upper mantle, a location where scientists generally did not expect earthquakes to occur.

Decades later, old data revealed a pattern. University of Utah researchers revisited the original seismic records and found that all nine events originated well below the crust, providing strong evidence for the existence of what scientists call continental mantle earthquakes (CMEs).

Their analysis confirmed that the unusual quake was real and part of a rare category of seismic events happening deep within Earth's mantle. The findings gained additional significance when another deep earthquake struck on September 10, 2025, near Maeser in Utah's Uinta Basin.

This type of earthquake occurs in an environment characterized by extreme heat and pressure. At such depths, rocks are generally expected to deform slowly rather than fracture suddenly.

To determine where earthquakes begin, seismologists examine the travel times of different seismic waves recorded by instruments at the surface. Small differences in arrival times help researchers pinpoint the earthquake's origin.

Why It Matters

This discovery helps scientists better understand how earthquakes occur and can improve our ability to predict when they might happen. This knowledge is important for people living in areas prone to earthquakes, such as India.

Key Facts

• A deep earthquake occurred beneath the town of Randolph in Utah on February 24, 1979.
• The earthquake was unusual because it happened at a depth of about 90 kilometers.
• Decades later, researchers confirmed that all nine events originated well below the crust, providing strong evidence for the existence of continental mantle earthquakes (CMEs).
• Another deep earthquake struck on September 10, 2025, near Maeser in Utah's Uinta Basin.
• This type of earthquake occurs in an environment characterized by extreme heat and pressure.

Key Terms

Continental mantle earthquakes (CMEs)

A rare type of earthquake that occurs deep within Earth's mantle.

Implications

This discovery helps scientists better understand how earthquakes occur and can improve our ability to predict when they might happen. This knowledge is important for people living in areas prone to earthquakes, such as India.