NPI's Cascadia Advocate

Offering commentary and analysis from Washington, Oregon, and Idaho, The Cascadia Advocate is the Northwest Progressive Institute's unconventional perspective on world, national, and local politics.

Friday, November 30th, 2018

Magnitude 7.0 earthquake shakes Anchorage, Alaska, causing widespread damage

A pow­er­ful mag­ni­tude 7.0 earth­quake shook the City of Anchor­age, its sub­urbs, and points beyond this morn­ing, caus­ing wide­spread dam­age in Alaska’s largest city. The quake was the strongest to hit the city in more than fifty years.

Thank­ful­ly, no fatal­i­ties have been report­ed, and build­ings through­out the region appear to be struc­tural­ly intact. How­ev­er, dam­age trans­porta­tion, elec­tric, ener­gy, and water infra­struc­ture appears to be rather exten­sive. Res­i­dents are grap­pling with pow­er out­ages, road clo­sures, and wrecked belong­ings.

It will be a long time before Anchor­age has recov­ered from this event.

Here’s a syn­op­sis of the quake from the Unit­ed States Geo­log­i­cal Sur­vey:

The Novem­ber 30, 2018, Mw 7.0 earth­quake near Anchor­age, Alas­ka, occurred as the result of nor­mal fault­ing at a depth of about 40 km.

Focal mech­a­nism solu­tions for the event indi­cate slip occurred on a mod­er­ate­ly dip­ping fault strik­ing north-south (dip­ping either to the east at about 30 degrees, or the west at about 60 degrees).

At the loca­tion of this earth­quake, the Pacif­ic plate is mov­ing towards the north­west with respect to the North Amer­i­ca plate at about 57 mm/yr, sub­duct­ing beneath Alas­ka at the Alas­ka-Aleu­tians Trench, approx­i­mate­ly 150 km south-south­east of this event. The loca­tion and mech­a­nism of this earth­quake indi­cate rup­ture occurred on an intraslab fault with­in the sub­duct­ing Pacif­ic slab, rather than on the shal­low­er thrust-fault­ing inter­face between these two plates.

Earth­quakes are com­mon in this region. Over the past cen­tu­ry, 14 oth­er M 6+ earth­quakes have occurred with­in 150 km of the Novem­ber 30, 2018 event. Two of these – a M 6.6 earth­quake in July 1983 and a M 6.4 event in Sep­tem­ber 1983 – were at a sim­i­lar­ly shal­low depth and caused dam­age in the region of Valdez.

The M 9.2 great Alas­ka earth­quake of March 1964, was an inter­face thrust fault­ing earth­quake that rup­tured over sev­er­al hun­dred kilo­me­ters between Anchor­age and the Alas­ka-Aleu­tians trench, and to the south­west.

And here’s a run­down of roads the quake left either com­plete­ly impass­able or unsafe to trav­el on from the Anchor­age Dai­ly News:

The Glenn and Seward high­ways in town reopened ear­ly Fri­day after­noon, accord­ing to an update from Anchor­age police. But detours and delays con­tin­ue. Dam­age was a mov­ing tar­get, with new updates still com­ing in Fri­day evening.

There were sev­er­al reports of seri­ous road dam­age. The Glenn High­way had closed north of Eagle Riv­er because of dam­age to the south­bound Eagle Riv­er bridge, and an on-ramp at the inter­change of Inter­na­tion­al Air­port Road and Min­neso­ta Boule­vard col­lapsed.

A sec­tion of high­way between Eklut­na and Mir­ror Lake cracked and crum­bled, clos­ing south­bound lanes for sev­er­al days, accord­ing to Alas­ka Depart­ment of Trans­porta­tion project engi­neer Rod Cum­mings. South­bound traf­fic will be rout­ed around the area until crews can repair the dam­age.

The Palmer exit off the high­way was closed after a gap appeared between the abut­ment and the bridge, offi­cials said.

Vine Road near Wasil­la also suf­fered major dam­age and a sec­tion is closed. From above, the heav­i­ly used con­nec­tor road looked like a giant bowl­ing ball hit it. Point MacKen­zie Road sus­tained seri­ous dam­age as well.

The City of Anchor­age and the State of Alas­ka have each declared a state of emer­gency. A request for fed­er­al assis­tance has already been approved.

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