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Anchorage shakes, West Coasters quake

by Greg Klein | November 30, 2018

“Waiting for the big one” comprises a fairly common West Coast refrain. So far on November 30 three destructive earthquakes have hit Anchorage. More may be coming.

The first and biggest, reaching magnitude 7 on the Richter scale, struck at 8:29 a.m. local time at an epicentre 13 kilometres north, according to the U.S. Geological Survey. Six minutes later a magnitude 5.7 emanated from four kilometres northwest of the city of almost 300,000 people. Nearly two hours later the Richter scale measured 4.9 at an epicentre 17 kilometres northwest.

Anchorage shakes, West Coasters quake

Police block traffic on a highway north of Anchorage
following the November 30 earthquakes.
(Photo: JT Fisherman/Shutterstock.com)

More shocks came from the town of Big Lake, about 35 crow-flying kilometres northwest of Anchorage, ranging in magnitude from 3.7 to 5.1.

By press time no deaths or serious injuries were reported. But highways and roads have been mangled out of shape, power has been knocked out, rail transport and the 1,290-kilometre Trans-Alaska pipeline have been shut down and at least one hospital has postponed non-emergency surgeries. A tsunami warning was issued and cancelled.

The Alaskan events serve as a warning to those living in tectonically troubled regions farther afield. Some of them have experienced lighter quakes just recently. One day earlier, magnitude 4 and 4.5 quakes struck near Fort St. John in northeastern British Columbia. A November 19 magnitude 4.1 event took place in the Juan de Fuca Strait 78 kilometres southeast of Sooke, B.C. The Pacific seafloor west of the northern Vancouver Island town of Port Alice had a busy autumn with six quakes measuring between 4.2 and 6.8 at epicentres between 233 and 174 kilometres southwest of the town. Other quakes in the last six months have struck the vicinity of Victoria on Vancouver Island’s southern tip and Port Hardy on the Island’s north, as well as the southern Vancouver suburb of Tsawwassen.

In fact about 400 quakes a year take place between northern Vancouver Island and Seattle, according to Natural Resources Canada, although only a dozen or so shake things up enough to grab people’s attention.

This region’s activity comes from the Cascadia Subduction Zone, a route running from the northern Island to California in which the oceanic Juan de Fuca Plate pushes its way beneath the continental North American Plate “at roughly the same rate as fingernails grow—about four centimetres per year,” NRCan explains.

Anchorage shakes, West Coasters quake

A common sign in coastal communities.

Quakes along the plate boundaries can reach a monumentally destructive 9 on the Richter scale. The region experiences them every 200 to 800 years, with the last occurrence in January 1700.

Getting back to Alaska, where the Pacific and North American plates rub each other the wrong way, magnitude 9.2 fell upon Anchorage, Seward, Valdez and other southern state locations on Good Friday 1964. The worst quake ever recorded after Chile’s magnitude 9.5 in 1960, it killed about 140 people amid widespread destruction. A tsunami hammered towns along the coasts of Alaska, northern B.C. and western Vancouver Island, reaching as far as Hawaii.

Today, West Coast communities tend to show awareness about seismic building standards, earthquake preparedness and tsunami evacuation routes. But that wasn’t always the case. The Cold War generation of 1964 likely worried more about Soviet nukes from above than tectonic tribulations below. That might explain why some Vancouverites, on that Good Friday in 1964, actually flocked to the shoreline to watch the “tidal wave” roll in.

Luckily for them, it spared their city.

The November 30 Anchorage quakes follow new earthquake preparedness legislation passed by U.S Congress just three days earlier.

 

Update: The earthquakes in the Fort St. John district were probably caused by fracking, a Geological Survey of Canada scientist told Canadian Press.

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