Will a megathrust earthquake strike the NW in 2013? Some clues emerging

Will a megathrust earthquake strike the NW in 2013? Some clues emerging

Published 5:47 pm, Wednesday, January 2, 2013

There were 4,800 earthquakes in the Northwest in 2012 and a record “episodic tremor and slip” event – a string of deep mini-quakes running from Vancouver Island to below Centralia – over the summer, but does any of that mean we’re likely to see the “big one” in 2013?

While the devastating megathrust quakes that happen every 300 to 500 years in our neck of the woods (those caused by the Juan De Fuca plate’s grinding collision and subduction with the North American plate) are still impossible to predict, some clues may be emerging.

An immature science

Taken together, last year’s quakes were “mild” since so few of them were big enough to be felt, said John Vidale, director of the Pacific Northwest Seismic Network.

The biggest and most interesting quake of the year struck under Victoria, B.C., last week. It was a magnitude 4 temblor and resembled in depth and fault the magnitude 6.8 Nisqually quake that damaged Seattle and shook the region in 2001, he said.

It was felt and reported to the network’s webpage by about 800 people.

He added that a string of unusual quakes around the globe has the seismic community baffled. A big earthquake off the coast of Sumatra in the Indian Ocean six months ago was “very strange” because of its size and distance from the plate boundary.

It showed “we can get earthquakes we really hadn’t anticipated,” he said.

In the past few years, China got hit with an earthquake on a fault that wasn’t mapped, New Zealand suffered a “very rare earthquake” …

“There’s a whole series of events in the last decade that give us the impression that we know less than ever,” Vidale said. “We keep thinking that these are the specific risks we need to look out for and then earthquakes happen that aren’t the ones we thought were most likely to happen.”

Also, a roughly annual seismic event in the Northwest discovered 12 years ago – the “episodic tremor and slip,”or ETS – went wild last summer.

Doing the ‘tremor and slip’

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Anteros Oberon
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