6.2 magnitude earthquake felt in Adak

A magnitude 6.2 earthquake struck 50 miles from Adak around 9 p.m. on Wednesday, Jan. 22, 2020. (Map by U.S. Geological Survey)

A magnitude 6.2 earthquake struck Wednesday night about 50 miles from Adak. There is no tsunami threat expected.

Ken Macpherson, a seismologist for the Alaska Earthquake Center, said this was a “crustal earthquake,” meaning it was relatively shallow, at a depth of about 10 kilometers (6.2 miles).

Houses built for military families on the north side of Adak, before the Base Realignment and Closure Act in 1995 led the Defense Department to shutter operations on the island by 1997. (Photo by Zachariah Hughes/Alaska Public Media)

“To give you an idea of how large that is, you get only about 100 magnitude 6 earthquakes on the globe annually,” said Macpherson. “So that’s a fairly significant earthquake.”

Adak residents felt the shallow earthquake, which followed a series of smaller quakes in the same area.

Macpherson also said there have been dozens of aftershocks.

“Some of them are in the magnitude 4 range,” he said. “We could see up to a magnitude 5. A general rule of thumb is that the largest aftershock will be about one whole magnitude less than the main shock.”

Macpherson said the activity is nothing out of the ordinary in the seismically active Aleutian Islands.

The quake struck near the Takawangha and Tanaga volcanoes. While there’s no evidence the event was volcanic in origin, the Alaska Volcano Observatory said scientists are monitoring for signs of unrest.

As of Thursday afternoon, the observatory has listed the alert levels for Takawangha and Tanaga volcanoes as “normal.”

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