A major earthquake centered in the Gulf of Alaska temporarily generated a tsunami warning for much of southern Alaska's coastline early Tuesday morning.

According to the U.S. Geological Survey, the 7.9 temblor was initially reported as an 8.0, then an 8.2. It struck at 12:31 a.m. 281 miles southeast of Kodiak, at a depth of 20 kilometers.

An 8.0 earthquake struck on Tuesday, Jan. 23, 2018 at 12:31 a.m. roughly 281 kilometers southeast of Kodiak. (From USGS)

tsunami warning for Alaska's southern coastline from the Aleutian Islands to Southeast Alaska, issued by the National Tsunami Warning Center in Palmer, was downgraded at about 3:15 a.m. to a tsunami advisory for the coastline east of Seward to Chignik Bay. It was canceled at about 4:15 a.m.

Anchorage police said there was never a tsunami warning in effect for the Anchorage vicinity.

Staff at the earthquake center said the quake was the largest to hit the Gulf of Alaska since the 1964 Good Friday quake which ravaged Southcentral Alaska and destroyed Valdez's original townsite. The most recent quake of the same magnitude was a 7.9 which struck the Aleutian Islands in 2014.

According to the tsunami center, the tsunami's arrival times and sizes in various Alaska towns were as follows:

Kodiak: 2:29 a.m., 0.6 feet
Seward: 2:21 a.m., 0.4 feet
Old Harbor: 2:38, 0.7 feet
Sitka: 2:18 a.m., 0.4 feet
Yakutat: 2:35 a.m., 0.5 feet

Kodiak police had advised people to go to higher ground, advising that nearby Pillar Mountain had  By 3 a.m., water levels in Kodiak's channel were fluctuating by up to 3 feet. Officers advised on the department's Facebook page that the advisory had been canceled by 4:30 a.m.

The Kodiak Island Borough School District canceled classes for the day due to the tsunami warning, according to its Facebook page, and Kenai Peninsula Borough School District schools in Homer, Seward and the southern Peninsula were starting two hours late in response.

Larry LeDoux, superintendent of schools in Kodiak, said about 600 people had gathered at the local high school. Everyone there was calm, with the Red Cross of Alaska setting up in case it’s needed.

Kodiak resident Paul Snyder said he was asleep at his Hemlock Street home when the quake hit. Although he didn't plan to evacuate, because the 1964 earthquake which ravaged Southcentral Alaska didn't produce a major tsunami in his area, many of his neighbors did.

"It woke me up; this quake woke me up," Snyder said. "This was moderate, it was kind of medium; it was not as bad as some of them, but I've never seen a reaction this bad."

Phillip “Bear” Becker, a Kodiak resident for more than 30 years, said the quake didn’t seem very violent but “lingered for probably well over a minute.”

“It was long and steady. It built up and it just sustained,” Becker said. “We always keep that 30-second rule: if something's over 30 seconds, then that’s significant.”

Teressa Muller and Larry Pestrikoff were among the people who had evacuated to higher ground in Kodiak.

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Sitka resident Brian Schultz took to Facebook with a video where you can hear the tsunami warning siren going off.

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Over in Seward, KTVA spoke with longtime resident, Jeannie Greene, who lived through the 1964 earthquake. Since then, she said tsunamis have always been on her mind. After hearing Tuesday morning's sirens, she feared for the worst.

"It really was going on and on and I yelled for my husband, I said, 'Dennis get up, earthquake,' and he thought I was messing around or something but I said 'Earthquake come on come on'", Greene said. "We had done a drill, believe it or not, like a month before that, on what would we grab, what would we take."

Alaska’s state seismologist, Michael West, said that no significant reports of damage had come in from the earthquake itself.

“Because the earthquake was really far off into the ocean, we are not aware of any apparent results from the ground-shaking part of the earthquake,” West said. “The tsunami has been an evolving situation, and the National Tsunami Warning Center has been on it from the very beginning.”

Unlike most earthquakes in the Alaska Subduction Zone, caused when the edge of one tectonic plate slides under another at the meeting of the North American and Pacific plates, West said Tuesday’s temblor was a “strike-slip” quake – caused when the edges of the two plates slid horizontally against each other.

“This is a different cause than the majority of the quakes in the magnitude-7-to-8 range we experience in this region in Alaska,” West said. “It was not caused by the same mechanism as, say, the 1964 earthquake; it was a different kind of event.”

On the Kenai Peninsula, Homer police said the Homer Spit and low-lying areas were being evacuated prior to the tsunami's arrival. Seward Fire Department officials said sirens went off right after earthquake, leading to "controlled chaos" as people evacuated.

In Alaska’s capital city, about a dozen families headed for higher ground early Tuesday. Most lived on boats along the Gastineau Channel and parked their cars several blocks uphill from the water.

Many in Juneau posted reports on social media sites, saying they felt the earthquake.

“The alarms went off on our phone,” said Juneau resident Jan Trigg. “We thought, ‘Why just lay in bed and watch this happen? We might as well come out where it’s safe and listen.’”

West said that scientists were likely to study seismic data from Tuesday’s quake in detail due to its magnitude. Significant follow-up quakes after the initial one were unlikely, however.

“We would not be surprised to see aftershocks inching into the 6, maybe 7-magnitude range; there is a small but real possibility that it could trigger some follow-on earthquake of the same size or bigger,” West said. “We have no reason to suspect

anything like that at this time – there’s every reason to expect this event is done.”

Tuesday morning, Caltech's Seismo Lab examined the earthquake.

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Emily Carlson, Manny Creech, Melissa Frey, Scott Jensen, Ken Kulovany and Steve Quinn contributed information to this story.

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