Your questions on Tuesday’s earthquake answered

IDAHO FALLS — Idaho has experienced more than 60 aftershocks and lots of questions after a powerful earthquake struck the Gem State on Tuesday evening.

More than 39,000 people reported to the USGS that they felt shaking all over Idaho and parts of Utah, Montana and Washington when the initial temblor hit. The magnitude 6.5 earthquake struck about 45 miles west of Challis and 20 miles northwest of Stanley just before 6 p.m. Tuesday, according to the U.S. Geological Survey. As of Wednesday evening, 67 aftershocks had been recorded.

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What made this earthquake different?

“Analysis of the seismometer shows that it was a strike-slip fault. … It moved horizontally. The left side moved south, and the right side moved north,” BYU-Idaho Professor of Geology and Geophysics Robert Clayton said. “But the location is kind of unusual. Usually, earthquakes are farther south or east from there, near Challis or south of Stanley.”

Idaho State University Professor of Geosciences Glenn Thackray seconds Clayton. He said there’s some surprise that the faults that cut through that area are active.

“There’s been suspicion but no confirmation that those faults are active,” Thackray said.

Omg… I just realized I recorded that entire earthquake… My camera was sitting on a table as I was getting ready to do a Facetime interview.
My significant other was taking a nap in the other room at the time (don't make fun of my freaked-out calls for him, LOL). pic.twitter.com/KvJRld2GDy

— KIVI Madeline White (@madelinewhiteTV) April 1, 2020

Over the past 50 years, no earthquakes of a magnitude 5 or greater have occurred within 30 miles of where this earthquake took place, USGS said.

Both professors said this is the second-largest earthquake in Idaho, after the 1983 Borah Peak earthquake. That one was a magnitude 6.9 and killed two people in Challis near the quake’s epicenter.

Clayton said aftershocks could go on for months, but he said they do get smaller over time.

“We’ve (probably) seen the only magnitude 4 or bigger aftershocks we’re going to have, although you never know,” Clayton said.

What does Tuesday’s earthquake mean for Yellowstone?

Some EastIdahoNews.com readers have wondered if Tuesday’s initial earthquake could trigger Yellowstone volcano activity. Clayton and Thackray both firmly said no.

“The reason that it’s a no is this earthquake is in a very different part of the region. There’s a lot of geology between this earthquake and Yellowstone,” Thackray said. “It’s a long way away and the effects at that location weren’t great.”

Thackray said Tuesday afternoon there were two small earthquakes in the West Yellowstone area. He said small earthquakes in the Yellowstone region are typical.

“Yellowstone does its own thing. That’s the best way to look at it,” he said. “Those (small earthquakes) were happening yesterday as well, totally independently of this one.”

Did Utah’s earthquake cause Idaho’s?

Clayton and Thackray said it’s not likely Utah’s recent earthquake caused Idaho’s earthquake.

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“There have been a few cases with very large earthquakes where we could demonstrate that they triggered another earthquake somewhere else, not that far away,” Clayton said. “Earthquakes can trigger other earthquakes. But a 5.7 down in Utah — it’s unlikely that it would trigger an earthquake 200 miles away.”

Thackray said as far as he knows, it’s a “complete coincidence.”

“Sometimes the shaking from one earthquake will stress another fault. But the shaking from the Salt Lake earthquake should have been almost nothing in the Stanley area where this one occurred,” Thackray said. “Any connection by the waves, there’s just so much rock for that to go through to have any effect.”

Does this earthquake say anything about future ones?

The problem with determining what this earthquake means for future Idaho earthquakes is tough because they are unpredictable.

“Earthquakes often don’t obey patterns in time,” Thackray said.

Clayton said quakes in Idaho have taken place in three areas. One area is from around Challis down to about Sun Valley and Ketchum, another around West Yellowstone and Hebgen Lake, and the third in the southeast corner of the state near Star Valley, Wyoming.

“There’s been some decades that have had two or three magnitude 6 earthquakes. Other decades had none,” Clayton said. “They don’t follow a regular pattern.”

Thackray said people need to be aware earthquakes can happen in Idaho. Clayton said more “sizable earthquakes” will occur in the future.

“I compare it to wearing seatbelts. It’s important to wear your seatbelt every time you get in the car because you never know when an accident will happen. If you don’t know when it’s going to happen, you have to be prepared all the time,” Clayton said. “Same thing goes with earthquakes. We know it will happen. We don’t know when — therefore, we need to be prepared all the time.”