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8.2 magnitude quake in Alaska’s Aleutian Chain generates small tsunami

A tsunami watch was issued for Hawaii following a large quake off Alaska
A tsunami watch was issued for Hawaii following a large quake off Alaska(Hawaii News Now)
Published: Jul. 29, 2021 at 5:02 AM CDT
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ANCHORAGE, Alaska (KTUU) - A preliminary 8.2 magnitude earthquake struck off the coast of the Aleutian Chain late Wednesday night, generating a small tsunami and prompting a tsunami warning and evacuations for several communities along the Gulf of Alaska coast, KTUU reported.

The tsunami warning has since been downgraded to an advisory.

The Alaska Earthquake Center originally reported an earthquake struck 66 miles southeast of Perryville in the Aleutian Chain at 10:15 p.m. Wednesday night, with a preliminary magnitude of 7.3. The U.S. Geological Survey has reviewed the quake and released a revised report of a preliminary 8.2 magnitude earthquake 91 kilometers, or about 56 miles, southeast of Perryville.

The USGS reports a depth of about 29 miles.

The quake is the largest since 1965, according to USGS earthquake records for Alaska.

An initial tsunami warning was issued for the Alaska Peninsula and the Aleutian Islands, according to the U.S. Tsunami Warning System. The warning included the Pacific coasts from Hinchinbrook Entrance to Unimak Pass, and from Unimak Pass to Samalga Pass.

It was downgraded to an advisory by 12:40 a.m. Thursday.

According to the Tsunami Warning System, a tsunami was generated by the earthquake, but the forecasted maximum tsunami height is less than a foot.

Jeremy Zidek, a spokesperson for the Alaska Department of Homeland Security and Emergency Management, said the state’s emergency operation center was activated and that staff was called in.

“We contacted Perryville, the community that’s closest to the epicenter,” he said. “Pretty sparsely populated out there. The folks in Perryville said that the shaking was very violent, and that they started their evacuations.”

Potential tsunami activity was originally forecasted to begin first in Sand Point at 10:55 p.m., to reach Seward around 12:20 a.m. and Homer around 1:15 a.m.

In Sand Point, where potential tsunami activity was estimated to begin first, Denise Mobeck sounded the alarm herself, literally. The community’s tsunami warning system is not automatic, she said, so when the quake happened, she had to go to where the alarm is located and activate it.

Mobeck is the administrator for the Sand Point Police Department. She said officers were also on the ground working on moving people to higher ground.

The earthquake seemed to last around 2 minutes, Mobeck said.

“It started getting stronger and stronger,” she said. “And I ended up going out into the living room because I started hearing glass break.”

Those in a tsunami advisory area were asked to be alert and follow instructions from local emergency authorities.

“Move out of the water, off the beach, and away from harbors, marinas, breakwaters, bays and inlets,” the advisory stated.

Several coastal communities had their residents evacuate to higher ground.

Zidek said the Department of Homeland Security and Emergency Management will be checking in on Perryville again to see if they need any assistance.

The emergency operation center contacted every community covered under the tsunami warning to make sure they received it, he said, and to make sure they took action.

Zikek said at this time, it’s not known what type of tectonic fault movement triggered the earthquake.

“Back a couple years ago, we had a 7.9 (magnitude earthquake) near Kodiak, and that was a slip strike fault, so the faults are moving past one another,” he said. “And that doesn’t really create a tsunami wave.”

The movement that generates larger and more dangerous tsunamis is when one edge of a fault drops and the other gains elevation, he said. What the Tsunami Warning Center can do with the types of sensors that they have is estimate potential wave arrival times, not what type of fault movement caused a quake.

“We have to wait until that first estimated arrival time comes and goes before we know if a wave has been generated,” Zidek said.

In Sand Point, Mobeck said she got reports of the dock and boats moving in the harbor. She and a neighbor watched the water move a few feet.

“We have a little island called Range Island, that’s ... kind of in the middle of where Sand Point is,” she said. “And the water was rising a couple feet.”

According to the National Tsunami Warning Center, a half-foot wave was detected in Sand Point, a 0.7-foot wave was detected in Old Harbor, Alaska, a 0.4-foot wave was recorded in King Cove, and another half-foot wave was recorded in Kodiak.

Since the initial earthquake struck, there have been subsequent earthquakes in the area, including three quakes of magnitude 5 or above, and one aftershock that was magnitude 6 or above.

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