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Originally posted by radpetey
Are they going to move up into the area that this thread covers??
Sep. 12, 2013: While there was a short burst of tremor in south-central Puget Sound on Sep 4, 2013, there was a clear and sustained period of tremor on Sep 7 and every day since then. Starting down dip (mostly west of Hood Canal) it moved first south a bit and then on Sep 11 seems to have jumped back slightly north and up-dip. This is a characteristic type of start to these ETS events. Since there have been false starts to these in the past we typically want to see ten days of tremor in a row before it is pretty much assured to be a real ETS thus we will wait for another several days before officially declaring a start.
Sep. 14, 2013:
Tremor continues and is definitely moving north. In fact between 13 and 14 Sep. it jumped from the northern Olympic Peninsula almost to southern Vancouver Island and seems to be significantly more down-dip (eastward) than the track of previous ETS events in this area. The speed with which it is moving seems quite unusual.
An intriguing feature is the variety of speeds and directions in which tremor migrates over the course of a slow-slip episode. Major episodes, such as the one shown in figure 4, migrate along the plate boundary at about 10 km/day. The progress is fitful hour by hour, but fairly steady day by day.
Sep. 16, 2013:
Oh dear, it may be dying out. There was only about 5 hours of weak tremor today located just south of yesterday's tremor. It may be trying to fill in the gap left when it jumped from the Olympic Peninsula to the southern coast of Vancouver Island late on Sep 13. This gap is well resolved by two diferent subnetworks of stations and is pretty unique in the record looking back to other tremor episodes. This gap is unusual enough to get the attemtion of Dr. Herb "ETS" Dragert of PGC who seems more than a little interested in such an observation. Herb looked into possible GPS signals and reports:
What I can add at this stage is that as of yesterday, I have not been able to resolve any displacements for GPS stations in the tremor region which is unusual for 9 days of tremor. This would be consistent with slip (if any) on the plate interface being very small at this stage (i.e. less than ~0.5 cm) or slip occurring deeper which would result in reduced surface displacements.