PSN-L Email List Message

Subject: Re: VLF Quakes?
From: "Larry Conklin" lconklin@............
Date: Mon, 1 Apr 2002 14:14:05 -0500

Hi Dave,

I found your post particuarly interesting.  My sister-in-law lives in
Olympia, WA, only a few miles from the Nisqualy quake epicenter.
Fortunately, she didn't have any significant damage, despite the fact that
her house is on the side of a hill.  When the not so silent quake occurred,
I was worried the the whole house might have ended up at the bottom of the


----- Original Message -----
From: "David Saum" 
Sent: Monday, April 01, 2002 2:03 PM
Subject: VLF Quakes?

> From 3/28 Seattle Times:
> Thursday, March 28, 2002 - 11:15 a.m. Pacific
> Feel that? If not, it may be a silent quake
> By Eric Sorensen
> Seattle Times science reporter
> ELLENSBURG - Western Washington is in the midst of an earthquake and a
> rather sizeable one, but have no fear: it's silent.
> Researchers at Central Washington University, reporting in tomorrow's
> issue of the journal Science, say the region has in fact gone through
> eight "silent earthquakes" since 1992. One in August 1999 released the
> energy of a magnitude 6.7 temblor, nearly as big as last year's 6.8
> Nisqually quake. But because the quakes stretch out over six to eight
> weeks, their energy is dissipated and barely noticeable.
> " 'Slow earthquake' is the other term that's been widely used for
> these," said Meghan Miller, a CWU geologist and lead author of the
> paper. "The earthquake thing is probably a little bit of a misnomer
> because there's no real shaking associated with the event. But that's
> what they're called and I kind of like the 'silent earthquake.' It's
> poetic."
> Miller and her colleagues were inspired by work published in Science
> last year by Herb Dragert, a research scientist with the Geological
> Survey of Canada in Sidney, B.C., on the 1999 quake. Both papers rely on
> measurements taken at global-positioning sensors arrayed from Seattle to
> Neah Bay and on the southern half of Vancouver Island.
> Ordinarily, the sensors show Western Washington creeping eastward about
> one-half of an inch a year. This is because the oceanic Juan de Fuca
> plate is moving east and under the North American Continental plate,
> forcing the continental plate to compress and move east. But every 14
> months or so, the compression in the continental plate eases and
> rebounds westward.
> This would be a problem if it rebounded all at once, letting loose a
> fast, powerful tremor in the upper plate and beneath the major
> population centers of Vancouver, B.C., Seattle and Portland.
> But researchers theorize that the movement of silent quakes takes place
> in a deep, warm and well-lubricated section of the Cascadia fault -
> where the two plates meet - avoiding the jerky motion that happens when
> more shallow, cold and stickier portions of the fault give way.
> The most recent silent quake began on Feb. 7 near Friday Harbor and has
> been spreading across the region for weeks.
> The quake is at least magnitude 6, Miller said.
> Researchers say understanding these quakes gives them a new tool for
> monitoring the Cascadia fault and how it can cause large earthquakes.
> While it probably won't help them predict when earthquakes will happen,
> it should help them prepare for the next large earthquake with better
> building codes and other safety measures in areas most likely to be
> affected.
> Eric Sorensen can be reached at 206-464-8253 or
> esorensen@.................
> ------
> ...David Saum
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