1,406 af­ter­shocks shake Alaska

Tremors con­tinue to rat­tle state since Fri­day

USA TODAY International Edition - - NEWS - Kristin Lam

Two days af­ter a mag­ni­tude 7.0 earth­quake struck near An­chor­age, Alaska is still shak­ing.

Since Fri­day's tremor, the strong­est to strike The Last Fron­tier since a 7.9 in the re­mote Rat Is­lands in 2014, the U.S. Ge­o­log­i­cal Sur­vey has recorded 166 af­ter­shocks of mag­ni­tude 3.0 or higher around An­chor­age as of 4:50 p.m. PST Sun­day, USGS geo­physi­cist Brad Aa­gaard told USA TO­DAY. Earth­quakes of 3 or higher are strong enough to be felt.

There have been hun­dreds of smaller dis­tur­bances: 1,406 af­ter­shocks of at least mag­ni­tude 1.0. The af­ter­shocks will oc­cur less fre­quently as time goes on, Aa­gaard said. Over the next week, the USGS has pre­dicted 84 to 610 af­ter­shocks of mag­ni­tude 3 or higher. Af­ter­shocks of at least 3 are more than 99 per­cent likely. There's an 88 per­cent chance of a mag­ni­tude 5 or higher, too.

An af­ter­shock stronger or as strong as the ini­tial one is un­likely, how­ever. The prob­a­bil­ity for an earth­quake of mag­ni­tude 7 or higher be­fore Dec. 8 is only 3 per­cent, said the USGS.

The lo­ca­tion of the earth­quake – near the sub­duc­tion in­ter­face at a depth of 25 miles be­neath the sur­face – raised the thresh­old for what mag­ni­tudes are felt at the sur­face, Aa­gaard said. The sub­duc­tion zone is the place where two litho­spheric plates come to­gether, one rid­ing over the other, ac­cord­ing to the USGS.

"If this had been a much shal­lower one, peo­ple re­ally would be feel­ing a lot more af­ter­shocks," Aa­gaard said. "So that is prob­a­bly help­ing to some ex­tent, in terms of peo­ple not feel­ing as many af­ter­shocks, be­cause they are oc­cur­ring deeper." The earth­quake Fri­day dis­rupted power and heav­ily dam­aged the only high­way run­ning north of An­chor­age.

The mag­ni­tude 7.0 quake, maybe re­mark­ably, did not cause widespread dam­age to struc­tures or col­lapse build­ings.


Ex­ca­va­tion work was un­der­way Satur­day on a high­way near Ek­lutna, Alaska, to pre­pare for repaving.

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