An 8.2-magnitude earthquake struck off the southern coast of Alaska late on Wednesday (July 28), prompting a tsunami warning for parts of the state and a tsunami watch as far as Hawaii. They were lifted within hours.
It was the largest earthquake in the United States in 50 years, seismologists said.
The earthquake was detected about 120km south-east of Chignik, Alaska, about 10.15pm local time, the US Geological Survey (USGS) said.
The earthquake was felt throughout the Alaska Peninsula and on Kodiak Island, the Alaska Earthquake Center reported. In Kodiak, tsunami sirens blared and people began moving to higher ground as word of the warning spread.
There were no immediate reports of damage.
The alert issued by the National Tsunami Warning Centre was in effect for about two hours across south Alaska, the Alaska Peninsula and the Aleutian Islands.
A tsunami watch was also briefly issued for Hawaii and cancelled a little over an hour later, Governor David Ige said on Twitter.
The National Weather Service office in Beach, Hawaii, had warned that “widespread hazardous tsunami waves are possible”, based on preliminary measurements of the quake.
Tsunamis form as a series of waves caused by a large or sudden displacement of the ocean, the Weather Service said, citing serious earthquakes below or near the ocean floor as the most common cause. The waves radiate outwards in all directions from the disturbance and can move across ocean basins.
The earthquake recorded on Wednesday was one of only 17 since 1990 of 8.2 magnitude or higher around the world, according to USGS data.
There were at least two dozen aftershocks recorded in Alaska, the USGS said. One of the largest, about 112km south-southeast of Perryville, on the Alaska Peninsula, measured a 6.1.
Earthquakes in Alaska are not uncommon. The Alaska Earthquake Centre reported more than 49,000 seismic events in the state and nearby regions in 2020. The centre also said Alaska recorded last year’s most powerful and third-most powerful earthquakes worldwide.
In December, a 6.4-magnitude earthquake struck off the coast of a remote area of southern Alaska, but it did not spark any tsunami warnings that could threaten the region’s sparely populated string of islands.
About six months earlier, a 7.8 quake struck an area offshore, south of the Alaska Peninsula, close to Wednesday’s main quake activity.
An earthquake with a magnitude of 7 jolted Anchorage in 2018, cracking buildings, damaging roads and buckling bridges.
A 9.2 earthquake struck the south-central part of Alaska in 1964, making it the most powerful quake to hit North America in recorded history. The ground shook violently over a huge area for about 4 ½ minutes. More than 125 people died, Anchorage was heavily damaged, and much of the young state’s infrastructure was destroyed.
