Strongest US earthquake in 56 years rocks state of Alaska, but barely leaves a trace

Residents evacuate Homer Spit after tsunami warning sounds.

The most powerful US earthquake in half a century has left Alaska mostly unscathed, thanks to the remote location and depth of its epicentre. 

The magnitude-8.2 Chignik Earthquake struck at 10:15pm local time on Wednesday, just off the Aleutian Islands, according to local officials.

It was the strongest felt in the United States since an 8.7 quake ripped through the western Aleutian Islands in 1965.

There were no immediate reports of injuries or damage to property.

Several Alaskan coastal communities were evacuated following the quake.

Among them was Seward on the Kenai Peninsula, south of Anchorage, where sirens blared and residents were told to move to higher ground.

But residents of Alaska's affected communities said they were still assessing impacts after their late-night evacuations to higher ground.

"Stuff fell down and all," said Alec Phillips of the Native Village of Perryville, the tribal government in the community closest to the earthquake.

The US Geological Survey (USGS) said the earthquake was at a depth of 32 kilometres.

It struck 105 kilometres south-east of Perryville, about 800 kilometres from Anchorage, Alaska's biggest city.

Tsunami warnings were lifted after residents in some Alaska coastal communities were evacuated. (Reuters: Brian Hudson)

Wednesday's earthquake triggered a tsunami warning and evacuations in several Alaska coastal communities.

Those warnings were later lifted.

In Alaska, small tsunami waves measuring under 30 centimetres above tide level were observed in Sand Point, Old Harbor, King Cove, Kodiak, Unalaska and Alitak Bay, according to the US National Tsunami Warning Center (NTWC).

'Strong and deep'

"Even if you were right on top of the earthquake, you'd still be 30 kilometres away from it because it was so deep," said Stephen Holtkamp, who works for the Alaska Earthquake Center at the University of Alaska Fairbanks.

The earthquake struck along a subduction zone where the Pacific plate dives under the North American plate, Mr Holtkamp said.

That particular section of the subduction zone, called the Aleutian megathrust, is a seismic hot spot, with thousands of earthquakes each year, according to the Alaska Earthquake Center.

Mr Holtkamp said Wednesday's earthquake was likely related to another powerful earthquake in the same area a year ago — the magnitude-7.6 Simeonof Island earthquake struck about 70 kilometres away on July 21, 2020.

Reuters/ABC