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Swift
2013-Apr-09, 02:25 PM
I thought people might be interested in this article about "slow slip" from Science News (March 23, 2013; Vol.183 #6)
LINK (http://www.sciencenews.org/view/feature/id/348786/description/Quakes_in_Slo-Mo)


Herb Dragert didn’t know what to make of his wayward station.

In the early days of GPS satellites, Dragert had set up four benchmarks in the bedrock of Vancouver Island, British Columbia, to watch how their positions changed over time. Maybe, he thought, he could capture the ground moving during the earthquakes that occasionally shake the Pacific Northwest.

But instead Dragert saw one of his stations, at Albert Head on the southern part of the island, throwing a slow-motion tantrum. Every year or two it would inch westward for a few weeks, then stop, then do it again. The movement was far too slow to be an earthquake, but too fast for the ordinary creep of tectonic plates.

Twenty years later, Dragert and his colleagues know that they were seeing something new and important at Albert Head. The phenomenon, known as “slow slip,” happens when two sides of a geologic fault shift the same amount as in a large quake, but over weeks to months rather than seconds. “It’s like an earthquake, only slower,” says codiscoverer Kelin Wang, who, like Dragert, is a geophysicist at the Geological Survey of Canada in Sidney, British Columbia.

Geologists are now learning that slow slip happens in all sorts of places, from Japan to New Zealand to Costa Rica. New discoveries reveal how slow slip serves as a transition between ordinary quakes at the surface and those in deeper parts of the Earth where rocks flow like softened butter. And because periods of slow slip have heralded several large recent quakes, including Japan’s 2011 Tohoku quake, studying slow-motion events could hint at new and better ways to anticipate the next big one.

Ara Pacis
2013-Apr-09, 06:52 PM
I recall seeing a documentary that mentioned places in California that move like that. Also, something about the Marianas Trench makes it slip instead of sticking then shaking loose, maybe it was talc.

beskeptical
2013-Apr-09, 11:13 PM
The Olympic Peninsula breathes up and down in ~19 month period (the OP article says 15 months?). It's fantastic stuff for we Cascadia Fault rupture worriers.

Slow-slip evolves into megathrust earthquakes in 2D numerical simulations (https://pangea.stanford.edu/research/CDFM/pdfs2/Segall2012b.pdf)

When is an ETS an ETS? (http://www.pnsn.org/blog/2012/08/20/when-is-an-ets-an-ets)

ETS event of Summer 2012 (http://www.pnsn.org/tremor/ets-event-of-summer-2012)

Tremor is going full speed under the Puget Sound (http://www.pnsn.org/news/articles/2012/09/23/tremor-is-going-full-speed-under-the-puget-sound)

Calif. quake model looks for 'big one' in NW (http://www.kgw.com/news/Computer-model-gives-insight-into-when-the-Big-One-will-hit-186243722.html)


What I read a long while back was the area bunches up, then slow slips back down like an inch worm. But I've not been able to find the older articles that talk about the area rising before the slip.


There is a place in So California that had a long slow slip a number of years ago. I read it in one of the summaries on the USGS web site.