Originally posted by PuterMan
Just an observation of course and maybe wrong but......
Episodic Tremor and Slip (ETS) is the name given to a process that occurs deep below the Earth's surface, along faults that form the boundaries of
tectonic plates. It involves repeated episodes of slow sliding, one plate over the other, of a few centimetres over a period of several weeks,
accompanied by energetic seismic noise, called tremor. Tremor is distinctly different from the seismic signals generated by earthquakes.
The simple fact that the slow slip is occurring indicates that the plates are moving. Perhaps you cannot apply logic to this, but to me that says all
is well and that while there is episodic tremor there will not be a mega-quake.
I am finding it a little difficult to get hold of tremor readings for the 100 years before the last big Cascadia quake, but I would not mind betting
that they were absent.
So are you saying that the back and forth GPS readings over the past week are residual movement from the last ETS event in the area that ended in
Oct 12, 2012 - Officially this ETS is over!
When I check the PNSN tremor map
for the past month, the Vancouver Island/Puget Sound/Olympic Mountains region
has been very quiet.
This is the movement that I posted about. Maybe it isn't significant
. I was just asking what others thought.
(Thumbnail is a sample of PNW stations (showing N-S movement) found at
(farthest left blue line shows end-date of ETS, 2nd blue line shows date of Mag 7.8 some 900km north of area)
I agree that the plates are moving, and the long-term GPS readings show that.
I was just curious about the 1.5-2.0 centimeter moves late in December.
Seems strange for such a large area of land to move so quickly without active ETS or earthquakes. I doubt the entire GPS satellite array experienced
a positioning glitch of some kind.
I'd love to see tremor data for the 100 years proceeding the last Mag 9, too! Heck, I'd love to understand the mechanism for the tremor: fluid
migration, miniscule stick-slip at the plate interface, something.
As far as applying logic to this, yes, I suppose my thought processes can be logically-handicapped at times. But I disagree with you that ETS leads
to an absence of mega-thrust danger.
I think we don't know.
and Happy New Year.
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