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Another earthquake shakes central Idaho. Here’s how big it was

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In this file photo, Idaho Transportation Department crews had to work to clear avalanches and rockslides from Idaho 21 after the March 31, 2020, earthquake shook debris into the road between Stanley and Lowman. 

STANLEY — Two weeks after central Idaho’s biggest earthquake of 2021, another one tied that record and it happened in almost the same spot.

A 4.0-magnitude quake shook Stanley at 5:47 p.m. Saturday, the U.S. Geological Survey reported. A second earthquake was recorded at 7:34 p.m. with a magnitude of 2.8.

The first one tied the 4.0-magnitude quake on Sept. 18, which shook 11 miles northwest of Stanley. Until Saturday, that was central Idaho’s only earthquake this year with at least a 4.0 magnitude.

Saturday’s first was centered 5.6 miles northwest of Stanley and the second was 6.2 miles northwest of Stanley.

One difference between Saturday’s earthquake and the one two weeks ago was that the USGS reported Saturday’s was likely not felt by most people in the Boise area, according to the Modified Mercalli Intensity Scale. The one two weeks ago had a larger reach and a greater likelihood of being felt in the Boise area, albeit still weak given the distance from where the earthquake originated.

Central Idaho has been producing earthquakes for the past year and a half. Scientists have been researching the Sawtooth fault since a 6.5-magnitude earthquake on March 31, 2020. An Idaho State University professor discovered the Sawtooth fault a decade ago.

Prior to September, the last earthquake in central Idaho with at least a 4.0 magnitude was Nov. 25, 2020.

The Sept. 18 earthquake happened at almost the exact same time as the end of the Boise State football team’s loss to Oklahoma State. Saturday’s quake was about 45 minutes after the Broncos lost their second straight home game.


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