Will a megathrust earthquake strike the NW in 2013? Some clues emerging
By JAKE ELLISON, SEATTLEPI.COM STAFF
Published 5:47 pm, Wednesday, January 2, 2013
[snip]
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'
The boundary between the Juan De Fuca plate offshore and the North American plate runs under the Puget Sound area from California up to Canada. That's where we get the megathrust quakes of magnitude 9 or better. Below that danger zone, deeper in the subduction, is where the ETS happens.
The tremor and slip this summer was "one of the biggest ETS events yet monitored," the seismic network reported in its blog. And that had the experts "ever so slightly nervous."...
