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Tsunami Warning Follows 7.8 Earthquake off Alaska Peninsula

The tsunami warning originally stretched from the Alaska Peninsula to Kodiak Island and the western Kenai Peninsula, sending Alaskans scrambling to higher ground in communities such as Kodiak, Sand Point, Unalaska and Homer.

by Anchorage Daily News, Anchorage / July 22, 2020
Locator map of earthquake in Alaska. TNS
 
(TNS) - A tsunami warning across a large swath of coastal Alaska triggered by a magnitude 7.8 earthquake off the Alaska Peninsula on Tuesday night was canceled early Wednesday after the officials determined the tsunami was no longer a threat.
 
The tsunami warning originally stretched from the Alaska Peninsula to Kodiak Island and the western Kenai Peninsula, sending Alaskans scrambling to higher ground in communities such as Kodiak, Sand Point, Unalaska and Homer.
 
Though some people in Anchorage received tsunami warning alerts, the Anchorage area was not at risk, said Louise Fode, warning coordination meteorologist with the National Weather Service.
 
In its notice of the tsunami warning cancellation, the National Tsunami Warning Center said that “a tsunami was generated by this event, but no longer poses a threat. Some areas may continue to see small sea level changes.”
 
The center also urged people not to return to hazard zones until local officials said it was safe to do so.
 
James Gridley, director of the National Tsunami Warning Center in Palmer, said in an interview early Wednesday that “our procedures put us into a warning even if we haven’t measured a tsunami wave — we imply that there is until we know better.”
 
The earthquake occurred at 10:12 p.m. Alaska Daylight Time on Tuesday about 75 miles south of Chignik at a depth of about 17 miles, and was reportedly felt as far away as Anchorage, according to the U.S. Geological Survey.
 
“This is a very significant earthquake in size,” said Michael West, state seismologist with the Alaska Earthquake Center.
 
The Tuesday night earthquake was “something like 15 times more energy than was released in the 2018 Anchorage earthquake,” he said. But since it happened offshore, there was much less shaking recorded, and West said earthquake center officials weren’t expecting damage from shaking.
 
The kind of earthquake that occurred Tuesday evening was typical for the southern coast of Alaska, West said. It’s also the same style — “more or less,” West said — as the Great Alaska Earthquake of 1964.
 
“These are the style of earthquakes which can be very tsunami-producing,” West said.
 
In Kodiak, tsunami warning sirens sounded Tuesday night and residents headed to high ground. Kodiak High School opened its doors for evacuees, as did the local Catholic school. At Coast Guard base Kodiak, residents were instructed to head to Aviation Hill, high ground overlooking the nearby airport. The local public radio station reminded evacuees to carry masks.
 
“We’ve got a high school full of people. I’ve been passing out masks since the first siren sounded,” said Larry LeDoux, superintendent of the Kodiak School District. ”Everything’s as calm as can be. We’ve got probably 300, 400 people all wearing masks,” he said.
 
At the Kodiak Police Department, where local officials had set up an emergency operations center, Officer Francis de la Fuente said they had not seen a wave by 12:15 a.m. “We’re just waiting for the tsunami warning center,” he said.
 
At Kodiak High School, LeDoux said the sirens and evacuations were nothing out of the ordinary for someone who grew up in Kodiak.
 
”I’ve been doing these since I was a little kid,” he said. “Old news.”
 
In the first minutes of a seismic event, there aren’t usually enough ocean sensors to measure a tsunami wave, said Gridley with the National Tsunami Warning Center. You have to give it time to get to nearby sensors, he said, but if there’s a wave, beaches and shorelines could be impacted before then.
 
“We have to assume the worst-case scenario,” Gridley said. “The safest position is to get people moving.” It’s not like a hurricane that forms out in the ocean, days away from shore, he said — they have to go straight to a warning.
 
On Tuesday, the center issued its tsunami warning and kept the warning in place after seeing a 25-centimeter, or nearly 10-inch, wave in Sand Point. Center officials knew the tsunami wouldn’t be huge, Gridley said, but they had to be certain and wait for the entire wave cycle.
 
“If we just start seeing a little bump, we don’t know if that bump is going to get much bigger, or if that was it,” Gridley said. After about an hour and a half Tuesday, the tsunami advisories for certain areas outside of the warning zones were canceled, Gridley said.
 
“We just had to wait long enough to see whether or not we would see more of a wave develop or not,” Gridley said. “And the answer was no.”
 
The center canceled the tsunami warning, which grew to stretch from the Aleutian Islands to the Western Kenai, a little under two hours after it issued its initial warning.
 
Unalaska City Manager Erin Reinders said the city activated its emergency operations center Tuesday night and notified the community to evacuate areas below 50 feet to higher ground, before later issuing the all-clear.
 
”We were in a (city) council meeting and started feeling it rocking, and by the time I got home from the council meeting then the warnings were going and had to turn back around,” Reinders said.
 
Kachemak Bay communities including Nanwalek, Port Graham, Seldovia, Homer and further inland up to the Fox River mudflats area fell under the tsunami warning, said Brenda Ahlberg, public information officer at the Kenai Peninsula Borough Office of Emergency Management, at 11:45 p.m. Tuesday. People in those areas were told to evacuate and go to higher ground, Ahlberg said.
 
”This is a developing situation, and we are monitoring closely the information that is coming from the state and federal agencies that we’re collaborating with,” Ahlberg said before the tsunami warning was canceled. “So at this juncture, I’m not putting a time stamp on it.”
 
 
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©2020 Alaska Dispatch News (Anchorage, Alaska)
 
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