Saturday 1 December 2018

Magnitude 7.0 Earthquake near Anchorage, Alaska.

The Alaska Earthquake Centre recorded a Magnitude 7.0 Earthquake at a depth of 40.9 km, about 13 km to the north of Anchorage, Alaska, slightly before 8.30 am local time (slightly before 5.30 pm GMT) on Friday 30 November 2018. There are no reports of any casualties associated with this event, but people have reported feeling it over a wide area of southern Alaska, and the event has caused some damage locally, including at least one roof collapse, and damage to highways and water mains that has left people without water and closed off several major transport routes. Over a hundred aftershocks have been recorded in the area since the initial quake.

Damage to a highway near Anchorage, Alaska, following an Earthquake on 30 November 2018. CNN.

Alaska lies on the North American Plate, with the Pacific Plate underlying the ocean to the south. The Aleutian Trench runs along much of the south coast of Alaska, with the Pacific Plate being subducted beneath this and passing under Alaska as it sinks into the Earth. Off the coast of southeast Alaska the Pacific and North American Plates pass one-another horizontally, with the Pacific Plate moving northward and the North American to the south (a transform plate margin). This is not a smooth process, and the plates frequently stick together, then break apart as the pressure builds up, causing Earthquakes.

 Model of the subduction of the Pacific Plat beneath the North American Plate along the southern coast of Alaska and the Aleutians. USGS.

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here.

 The approximate location of the 30 November 2018 Anchorage Earthquake. USGS.

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