Aftershocks of 1959 earthquake rocked Yellowstone in 2017-18

May 23, 2019

On Aug. 17, 1959, back when Dwight D. Eisenhower was president, the U.S. had yet to send a human to space and the nation's flag sported 49 stars, Yellowstone National Park shook violently for about 30 seconds. The shock was strong enough to drop the ground a full 20 feet in some places. It toppled the dining room fireplace in the Old Faithful Inn. Groundwater swelled up and down in wells as far away as Hawaii. Twenty-eight people died. It went down in Yellowstone history as the Hebgen Lake earthquake, with a magnitude of 7.2.

And in 2017, nearly 60 years and 11 presidents later, the Hebgen Lake quake shook Yellowstone again. A swarm of more than 3,000 small earthquakes in the Maple Creek area (in Yellowstone National Park but outside of the Yellowstone volcano caldera) between June 2017 and March 2018 are, at least in part, aftershocks of the 1959 quake. That's according to a study published in Geophysical Research Letters by University of Utah geoscientists led by Guanning Pang and Keith Koper.

"These kinds of earthquakes in Yellowstone are very common," says Koper, director of the University of Utah Seismograph Stations. "These swarms happen very frequently. This one was a little bit longer and had more events than normal."

"We don't think it will increase the risk of an eruption," Pang adds.

A long seismic tail

Taken together, the more than 3,000 small quakes of the Maple Creek swarm can be divided into two clusters. The northern cluster consists of Hebgen Lake aftershocks. The quakes fell along the same fault line, and were oriented the same way, as the Hebgen Lake event. Also, the team didn't see signs that the northern cluster was caused by movement of magma and other fluids beneath the ground.

Koper and Pang says it's not unheard of for aftershocks of a large earthquake to continue decades after the initial event. Pang, for example, has also studied aftershocks as recent as 2017 from the 1983 Borah Peak earthquake in central Idaho.

"There are formulas to predict how many aftershocks you should see," Koper says. "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."

A second culprit

The southern cluster of the Maple Creek swarm seems to have a different origin. Although the northern cluster was lined up with the Hebgen Lake fault, the southern cluster's lineup was rotated about 30 degrees and the quakes were about 0.6 miles (1 kilometer) shallower than the northern cluster.

So, the researchers concluded, although the shaking in the northern cluster influenced the southern cluster, the primarily cause of the southern shaking was likely subsurface movement of magma.

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

Koper says that the results highlight how earthquakes are different than other natural hazards. Floods, hurricanes or wildfires are over when they're over. "Earthquakes don't happen as a single discrete event in time," he says. The specter of aftershocks can continue for months, years or even, as Maple Creek shows, decades.
Find the full study here. The study was funded by the United States Geological Survey, the Brinson Foundation and the Carrico Funds.

University of Utah

Related Earthquakes Articles from Brightsurf:

AI detects hidden earthquakes
Tiny movements in Earth's outermost layer may provide a Rosetta Stone for deciphering the physics and warning signs of big quakes.

Undersea earthquakes shake up climate science
Sound generated by seismic events on the seabed can be used to determine the temperature of Earth's warming oceans.

New discovery could highlight areas where earthquakes are less likely to occur
Scientists from Cardiff University have discovered specific conditions that occur along the ocean floor where two tectonic plates are more likely to slowly creep past one another as opposed to drastically slipping and creating catastrophic earthquakes.

Does accelerated subduction precede great earthquakes?
A strange reversal of ground motion preceded two of the largest earthquakes in history.

Scientists get first look at cause of 'slow motion' earthquakes
An international team of scientists has for the first time identified the conditions deep below the Earth's surface that lead to the triggering of so-called 'slow motion' earthquakes.

Separations between earthquakes reveal clear patterns
So far, few studies have explored how the similarity between inter-earthquake times and distances is related to their separation from initial events.

How earthquakes deform gravity
Researchers at the German Research Centre for Geosciences GFZ in Potsdam have developed an algorithm that for the first time can describe a gravitational signal caused by earthquakes with high accuracy.

Bridge protection in catastrophic earthquakes
Bridges are the most vulnerable parts of a transport network when earthquakes occur, obstructing emergency response, search and rescue missions and aid delivery, increasing potential fatalities.

Earthquakes, chickens, and bugs, oh my!
Computer scientists at the University of California, Riverside have developed two algorithms that will improve earthquake monitoring and help farmers protect their crops from dangerous insects, or monitor the health of chickens and other animals.

Can a UNICORN outrun earthquakes?
A University of Tokyo Team transformed its UNICORN computing code into an AI-like algorithm to more quickly simulate tectonic plate deformation due to a phenomenon called a ''fault slip,'' a sudden shift that occurs at the plate boundary.

Read More: Earthquakes News and Earthquakes Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to