After the earthquake at about 9.30am GMT, the Alaska Earthquake Center said the epicentre was located about 175 miles south east of Kodiak City.
“No reports of damage yet, but we have felt reports from across the state,” the centre tweeted. “This quake was felt very widely, with even a few reports from Whitehorse.”
National Tsunami Warning Center has now cancelled tsunami warnings and watches which had stretched all the way from Alaska down the West Coast of America.
But a tsunami advisory has been issued for South Alaska and the Alaska Peninsula from Hinchinbrook Entrance to Chignik Bay, Alaska.
The National Tsunami Warning Center said: ”A tsunami has been confirmed and some impacts are expected.”
At 11.46am GMT, the Alaska Earthquake Center tweeted: “Given the location and type of mainshock, we anticipate vigorous aftershocks in the magnitude 4-5 range and can expect aftershocks of magnitude 6 or larger.
“We have no reason to suspect a follow-on earthquake of comparable, or larger, size than the M7.9 mainshock.
“Regarding aftershocks: The largest is ~M5 as of 2 hours into the sequence.
“It looks like the aftershocks extend North-South, suggesting the fault ruptured along along a North-South oriented fault.”
For the latest list of aftershocks and earthquakes visit the Alaska Earthquake Center website. The US Tsunami Warning System website has all the latest warnings.
The Pacific Tsunami Warning Center said: “Based on all available data a tsunami may have been generated by this earthquake that could be destructive on coastal areas even far from the epicenter.“
The USGS has released a “tectonic summary” of the 7.9-magnitude earthquake and how it was caused.
The report read: “The January 23, 2018 M 7.9 earthquake southeast of Kodiak Island in the Gulf of Alaska occurred as the result of strike slip faulting within the shallow lithosphere of the Pacific plate.
“Focal mechanism solutions indicate faulting occurred on a steeply dipping fault striking either west-southwest (left lateral) or north-northwest (right lateral).
“At the location of the earthquake, the Pacific plate is converging with the North America plate at a rate of approximately 59 mm/yr towards the north-northwest.
“The Pacific plate subducts beneath the North America plate at the Alaska-Aleutians Trench, about 90 km to the northwest of today’s earthquake.”