Yellowstone feels earthquake aftershocks – 60 years later

A gargantuan number of earthquakes hit Yellowstone National Park in 2017 and 2018, sparking worries that they could eventually trigger an eruption of the world's largest super volcano.

But a new study suggests that the 'quakes may have actually been aftershocks from another seismic event — 60 years prior.

The research, published in the scientific journal Geophysical Research Letters, looks at the 3,345 earthquakes that occurred near Maple Creek, Yellowstone, between June 12, 2017, and March 13, 2018, and found that a significant number of the earthquakes came from the same fault line and direction as the 1959 Hebgen Lake earthquake.

Map of the Maple Creek swarm, made using data from the U Seismograph Stations. (Credit: USGS)

Map of the Maple Creek swarm, made using data from the U Seismograph Stations. (Credit: USGS)

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"We find that the 2017–2018 Maple Creek sequence differs from the three previous large swarms in that many of the earthquakes can best be categorized as late aftershocks of the 1959 ... Hebgen Lake earthquake," the researchers wrote in the plain language summary. The Hegben Lake earthquake had a 7.2 magnitude and was responsible for the deaths of 28 people.

“These kinds of earthquakes in Yellowstone are very common,” said University of Utah geoscientist and the study's co-author, Koper, in a statement. “These swarms happen very frequently. This one was a little bit longer and had more events than normal.”

Unlike other natural disasters such as floods, hurricanes or wildfires, Koper added that earthquakes can continue for long periods of time. “Earthquakes don’t happen as a single discrete event in time,” he said.

Damage from the August 1959 Hebgen Lake earthquake. (Credit: I.J. Witkind/USGS)

Damage from the August 1959 Hebgen Lake earthquake. (Credit: I.J. Witkind/USGS)

Though unusual, earthquakes sending out tremors years later is not unheard of. Koper and Pang cited the examples of the 1983 Borah Peak earthquake in central Idaho which sent out aftershocks as late as 2017.

“There are formulas to predict how many aftershocks you should see,” Koper continued. “For Hebgen Lake, there looked like a deficit in the number of aftershocks. Now that we’ve had these, it has evened things out back up to the original expectations.”

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Koper and the study's lead author, Guanning Pang, have attributed roughly half of the 2017 and 2018 earthquakes to the Hebgen Lake 'quake, but the other half appear to have a different origination. They believe that it was from magma moving around below the surface, as the southern cluster was rotated 30 degrees and approximately 0.6 miles shallower than the northern cluster.

“We do consider it to be one swarm all together,” Koper said. “Because they were so close, there was some feedback and influence between the two sections.”

Plot of magnitude versus time in color-matched subsets of earthquakes. The warm colors mark earthquakes in the northern cluster and the cool colors mark the earthquakes in the southern cluster. (Credit: Univ. of Utah)

Plot of magnitude versus time in color-matched subsets of earthquakes. The warm colors mark earthquakes in the northern cluster and the cool colors mark the earthquakes in the southern cluster. (Credit: Univ. of Utah)

But what about those who worried that the increase in seismic activity would cause the world's largest super volcano to erupt, disrupting nearly everything in its path? You have nothing to worry about, according to the researchers.

“We don’t think it will increase the risk of an eruption," Pang added.

Phew.

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