On March 18, a magnitude 5.7 earthquake hit Salt Lake City, Utah, which was the state’s strongest quake since 1992, and less than two weeks later a magnitude 6.5 earthquake struck near Ruffneck Peak in the Sawtooth Mountains of Central Idaho. There were no deaths or major injuries recorded by either event, but their proximity to the Yellowstone supervolcano raised eyebrows among locals who feared they could spark a supereruption. Almost two months on, the USGS is getting calls from concerned members of the public, who are still feeling the ground rumbling.
Professor Poland took to YouTube at the start of May to explain why these events could still be felt by those that live near the caldera of Yellowstone.
He said: “I wanted to address some of the earthquake activity that we’ve been asked quite a lot about by the public.
“Some of the earthquakes are ongoing in Idaho, and also in the Salt Lake City area.
“Now these are aftershock sequences, from the strong events that happened near Salt Lake City on March 18.
Mike Poland spoke on Youtube this month
“There was a magnitude 5.7 earthquake and also a magnitude 6.5 in central Idaho on March 31.”
Prof Poland went on to explain how these aftershocks could continue for some time.
He added: “The aftershock sequence are the faults readjusting after these major events, kind of like a house settling in a way.
“The stress field changes, and so the faults have to adjust and you get a lot of these earthquakes that tend to tail off over time.
“The larger the earthquake, the longer the aftershock sequence can last.
“So, in Idaho, we might expect to see aftershocks that are ongoing for a year, at least many many months, although, this will gradually tail out over time.”
Prof Poland claimed he understood why the public would be worried about the aftershocks, but stated they were not linked to the caldera itself.
He added: “Still, very unnerving because most of these events are felt, but they are just aftershock sequences and are not related to any magmatic activity, even though it has the look of a swarm of earthquakes of the type that we see in Yellowstone.
“These are related to the settling of faults after the events that occurred in mid to late March.”
The Yellowstone volcano gets its nickname as a supervolcano due to its capability to inflict global devastation during a supereuption.
This has happened three times in the past, 2.1 million years ago, 1.3 million years ago and 630,000 years ago, leading some to claim it is overdue another.
But, the USGS has previously put minds at ease regarding any “overdue” claims.
Yellowstone Volcano Observatory’s Scientists-in-Charge Jacob Lowenstern said in 2014: “When you see people claiming it’s overdue, usually the numbers they come up with say the last eruption was 640,000 years ago, but it erupts every 600,000 years.
“But, in fact, if you average the eruption intervals, there’s 2.1 million to 1.3 million and then another 640,000 years ago.
“If you average those numbers you come up with something that’s over 700,000 years.
“So, in reality, even if you tried to make this argument, it wouldn’t be overdue for another 70,000 years.”