Alaska saw largest earthquake in the world in 2020, review states

Alaska sees world's first and third largest quakes of 2020
Alaska sees world's first and third largest quakes of 2020(KTUU)
Published: Feb. 26, 2021 at 9:38 PM AKST
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ANCHORAGE, Alaska (KTUU) - Two of the top three largest earthquakes recorded worldwide in 2020 happened in Alaska. The state also had the third highest number of earthquakes recorded in a year in 2020, only behind 2018 and 2019, according to the Alaska Earthquake Center’s 2020 seismicity review.

“It’s not uncommon for us to have large earthquakes in Alaska. In any given year, we could rank anywhere in the top five earthquakes worldwide,” Lea Gardine, an Alaska Earthquake Center seismologist, said.

In July, a magnitude 7.8 earthquake struck just south of Simeonof on the Aleutian Chain — the largest earthquake in the world in 2020. In October, the same area saw a magnitude 7.6 aftershock, which was the third largest, according to the review.

Both caused damage and generated small tsunamis.

Gardine said the proximity of the two big quakes makes them interesting.

“The fact that the third largest was an aftershock of the largest is actually pretty fascinating because typically you don’t have such large aftershocks, at least not so close in magnitude,” Gardine said.

She noted their location in the state makes them unique, too.

“The area in which these earthquakes occurred has been of interest to scientists, almost going back to the 1964 earthquake. Nearly every portion of the Aleutian Megathrust ruptured at some point except, at least that we’re aware of, except for this area known as the Shumagin Gap,” she said. “The 7.8 appears to partially fill in that gap.”

The Aleutian Megathrust fault and the Shumagin Gap
The Aleutian Megathrust fault and the Shumagin Gap(KTUU)

There were many aftershocks in the Simeonof region. Aftershocks from the 2018 magnitude 7.1 earthquake near Anchorage also continued in 2020.

According to the review, there was an average of 26 aftershocks from the Nov. 30, 2018 quake each week last year. The biggest was a 5.1 on Nov. 7, 2020.

About 1,200 aftershocks were reported in 2020 from the 2018 earthquake, bringing the total amount of aftershocks since the quake to over 12,000. This contributed to 2020 being named the third largest year for the number of quakes, with a total of about 49,250 seismic events in Alaska and nearby regions.

Gardine said the year with the most amount of earthquakes recorded was 2018; it had about 55,000. In second is 2019 at around 50,000 recorded seismic events.

“2018 and 2019 had some very notable seismic sequences, some very notable earthquakes, the magnitude 7.1 Anchorage earthquake, the 7.9 offshore Kodiak, the Kaktovik earthquake on the North Slope. So there were some very, very noteworthy sequences that occurred in 2018, continued into 2019. And actually still continued into 2020,” she said.

Alaska is also still seeing aftershocks from the 6.4 magnitude Kaktovik quake in 2018, which was the largest earthquake ever recorded on the North Slope, according to the review.

Over the last several years, Gardine said more monitoring equipment has been placed, which may factor into the rise of reported quakes.

Gardine said it is always important to be prepared for earthquakes.

“Earthquakes can happen any time of day, any time of year, any magnitude. And it’s very, very important to not let down your guard. So it’s important to make sure that you’re always prepared, or that at least you have some earthquake awareness in your mind,” she said.

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