Earthquake Hits Near Alaska, But Tsunami Warnings Cancelled
By Roxanne Palmer | January 6, 2013 3:17 AM EST
A magnitude 7.5-magnitude earthquake that struck off the coast of Alaska at about 4 a.m. EST time generated a tsunami, but the monster wave posed no threat to land, according to officials.
Tsunami warnings were issued for parts of Alaska and Canada shortly after the earthquake struck about 60 miles west of Craig, Alaska, but were canceled after the Alaska Tsunami Warning Center found that areas were seeing only small sea level changes.
The quake was the result of the Pacific and North America continental plates bumping together in a fault area known as a “strike-slip,” according to the U.S. Geological Survey. Strike-slips are where a fault between two tectonic blocks is nearly vertical, and where the blocks have moved mostly horizontal along the fault.
Saturday's earthquake has been pinpointed to what's known as the Queen Charlotte fault system, which has been involved in eight earthquakes with a magnitude of 6.0 or greater over the past 40 years, according to the USGS. An 8.1-magnitude earthquake struck in 1949, 230 kilometers (143 miles) southeast of the site of this latest earthquake.
Scientists say the Jan. 5 earthquake is connected to a 7.8-magnitude earthquake centered off the coast of British Columbia that occurred last October, sparking warnings that stretched all the way to Hawaii -- but which, like Saturday's tsunami, proved relatively harmless.
This latest quake “is an expression of deformation along the same plate boundary system,” the USGS said.
Undersea earthquakes lead to tsunamis when they cause the sea floor to deform in a way that vertically displaces the water above it, generating a powerful wave.
The 2011 Tohoku earthquake that led to widespread devastation in Japan was vastly stronger than any of the recent quakes centered off of Alaska, ranking a 9.0 on the moment magnitude scale used by seismologists to quantify earthquakes. Though the difference in measurements on the scale might seem small, a 9.0-magnitude earthquake is about 178 times stronger than a 7.5-magnitude earthquake.
Though a 7.5 magnitude earthquake is pretty powerful, it isn't rare -- there were 12 such earthquakes across the globe in 2012 alone, according to the USGS. But the vast majority of the 16,667 earthquakes that occurred last year registered between 2.0 and 6.0 on the moment magnitude scale.
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