This week's earthquake 'swarm' was 'very standard' Yellowstone stuff

JACKSON – Scientists have called a swarm of about 60 earthquakes under Yellowstone Lake on Tuesday and Wednesday “normal.”

Bob Smith, the University of Utah geologist who wrote the book on Yellowstone National Park’s geology, and Michael Poland, the scientist in charge of the Yellowstone Volcano Observatory, said as much Wednesday afternoon.

“It’s background, normal seismicity,” Smith said.

He said the northern part of Yellowstone Lake where the earthquakes occurred has seen a lot of tremors over the years. It’s right on the edge of a magma reservoir to the west.

The “swarm,” which occurred over two days, included two larger magnitude 3.1 and 3.7 earthquakes. In a press release, the University of Utah said that 44 earthquakes of magnitude 3.0 or higher have occurred within 16 miles of the magnitude 3.7 earthquake since 1962.

The largest was a magnitude 3.9 earthquake reported in 2008, about four miles south-southeast of Fishing Bridge. One larger magnitude earthquake, a magnitude 4.8 tremor, has been recorded within 32 miles of the recent seismicity: 2.8 miles north of Norris in 2014.

Swarms of earthquakes are exactly what they sound like. They’re a sequence of mostly small tremors with no “main shock,” or primary earthquake, according to the U.S. Geological Survey.

Poland said they’re also incredibly common in Yellowstone.

“Sixty events is not much,” Poland said. “We’ve had swarms with thousands of earthquakes that have lasted months. This is pretty garden variety for Yellowstone.”

Poland, however, said that earthquakes in the Greater Yellowstone Ecosystem pose a far greater risk to humans than any other seismic activity — once they reach a certain size.

The 1959 Hebgen Lake earthquake, for example, was a magnitude 7.3 convulsion that rumbled just outside Yellowstone’s western boundary. It caused a large landslide that carried some 50 million cubic yards of debris into a canyon, partially burying a campground on the valley floor and killing at least 28 people.

While none of the slides reported over the past few days come close to that magnitude, Poland said hullabaloo over the Yellowstone Supervolcano can distract from more pressing geologic dangers.

“That sort of hazard is real and under-appreciated in many ways by folks that look at these earthquakes and think it’s ‘volcano, volcano, volcano,’ ” he said.

Poland said the earthquakes are not a harbinger of volcanic activity: “Volcanoes are like people; they have personalities. Yellowstone’s personality is to be noisy. It makes a lot of earthquakes all the time.”

The Yellowstone Caldera occupies substantial space in the world’s collective imagination. A Russian pundit recently suggested nuking Yellowstone would activate the volcano, which scientists said wasn’t true.

But the park’s resident magma pit has a reputation for opening its mouth without putting any muscle behind it.

The University of Utah encouraged people who may have felt this week’s earthquakes to report them at Earthquake.USGS.gov.

Doing so helps researchers like Poland and Smith determine the impacts of earthquakes, and how different people feel earthquakes of different magnitudes and at different depths.

This story was published on March 30, 2023.