NWS had issued a tsunami warning after a 7.5-magnitude earthquake off the coast of Alaska. Tsunami warnings were in effect for the Pacific West coast. Hawaii was not facing a destructive tsunami threat according to the National Weather Service on Jan. 5, 2013.
While no tsunami warning was in effect for Hawaii, the National Weather Service (NWS) does advise that some coastal areas in Hawaii could experience small non-destructive ocean seal level changes and strong or unusual currents on Jan. 5, 2013.
Tsunami warnings had been issued by the West Coast and Alaska Tsunami Warning Center.
The tsunami warnings were especially in effect for parts of southern Alaska and coastal Canada, areas closer to the 7.5-magnitude earthquake. The affected areas include coastal areas from Cordova, Alaska to Vancouver Island, Canada.
The tsunami warnings were following a powerful earthquake which occurred in the Pacific Ocean off the coast of Alaska around midnight from Friday to Saturday.
The earthquake’s epicenter was located about 63 miles west of Craig.
In its Tectonic Summary, USGS reports that the Jan. 5, 2013, earthquake off the west coast of southeastern Alaska happened “as a result of shallow strike-slip faulting on or near the plate boundary between the Pacific and North America plates. At the location of this earthquake, the Pacific plate is moving approximately northwestward with respect to the North America plate at a velocity of 51 mm/yr.”
According to the United States Geological Service (USGS), the earthquake is most likely deriving from the movement of the Queen Charlotte fault system offshore of British Columbia, Canada, “which forms the major expression of the Pacific: North America plate boundary in this region. “
During the past 40 years, eight other earthquakes of a magnitude 6 or greater have occurred in this region. About 230 km south east of today’s earthquake, a 8.1-magnitude earthquake occurred in 1949. In 2012, a 7.8-magnitude earthquake happened about 330 km south east of today’s earthquake.
USGS reports that today’s earthquake “is related to that Haida Gwai earthquake three months previously, and is an expression of deformation along the same plate boundary system.”
Today’s earthquake was originally reported as a 7.7-magnitude earthquake but was later downgraded to a 7.5-magnitude earthquake. Aftershocks of about 4.7-magnitude continued WSW of Craig, Alaska.
The National Weather Service cancelled the tsunami warning after no damaging waves occurred as expected. About 3:30 a.m. on Jan. 5, 2013, NWS reports in its update that,
"SEA LEVEL READINGS INDICATE A TSUNAMI WAS GENERATED. IT MAY HAVE BEEN DESTRUCTIVE ALONG COASTS NEAR THE EARTHQUAKE EPICENTER. FOR THOSE AREAS - WHEN NO MAJOR WAVES ARE OBSERVED FOR TWO HOURS AFTER THE ESTIMATED TIME OF ARRIVAL OR DAMAGING WAVES HAVE NOT OCCURRED FOR AT LEAST TWO HOURS THEN LOCAL AUTHORITIES CAN ASSUME THE THREAT IS PASSED. DANGER TO BOATS AND COASTAL STRUCTURES CAN CONTINUE FOR SEVERAL HOURS DUE TO THE CONTINUING SEA LEVEL CHANGES AND RAPID CURRENTS. AS LOCAL CONDITIONS CAN CAUSE A WIDE VARIATION IN TSUNAMI WAVE ACTION THE ALL CLEAR DETERMINATION MUST BE MADE BY LOCAL AUTHORITIES.NO TSUNAMI THREAT EXISTS FOR OTHER COASTAL AREAS IN THE PACIFIC ALTHOUGH SOME OTHER AREAS MAY EXPERIENCE SMALL NON-DESTRUCTIVE SEA LEVEL CHANGES LASTING UP TO SEVERAL HOURS."