• June 4, 2009 - YEP. The AofA has missed this early ETS totally. It is now over and we had no new instruments installed. Fickle tremor! Garry Rogers of PGC (besides laughing at us) reports that there were two other back-to-back ETS-events determined by old seismic records only for which the inter-ETS times were less than a year. So when will the next one be? We should be ready for anything between early next spring and late next summer. Uhmmmm. In the mean time we will play at learning how to install, operate and interpret the data from 7-8 20-station arrays.
• May 23, 2009 - OH DEAR! This ETS came almost three months early and is now mostly over. Starting about April 27 in the southern Puget Sound and gaining hours and strength over the next week it seemes to have peaked, passing under the northern Olympic Pinensula coast on or about May 10 and then moving into southern Vancouver Island shortly there after. It now seems mostly over from our perspective with the PGC still reporting some tremor in south central Vancouver Island.
  This is playing havoc with the planned AofA experiment. We had counted on the ETS going off in July or August. The planned install time was early to mid June. Some of the equipment is still arriving. Currently our plans are to go ahead and install the arrays, run the full complement for a couple of weeks to get some background data (maybe some minor tremor if we are lucky) and then remove the Texans and turn off some of the RT-130s to conserve batteries. Later in the fall (or if tremor seems to pick up again) we will power back up some/most of the arrays to run through the spring and for the next ETS. It will arrive either early or late or on time, we are sure.
• May 10, 2009 - Tremor seems to be continuing and maybe increasing in the south Puget Sound area with some also to the north along Hood Canal.
• May 4, 2009 - Based on Aaron's automatic tremor location he reports ~60 hours of tremor during the last week and placed a request to Tim Melbourne to check on possible GPS signals from thouthern Puget Sound. He also reports the following "interesting observations":
  1. Using the same methodology and stations, I have now detected mores inter-ETS tremor since the May '08 event than I did between the '07 and '08 events. 206 hours now vs. 181 between '07 and '08 ETS.
  2. This tremor seems to be migrating north toward a region that just had 68 hours of localized tremor activity in March. With the hypothesis that the March "episode" bled off moment, I'm curious to see if the current tremor area migrates through this region or stops short of it.
• April, 2009 - Orders for equipment and batteries for this summer's experiment were finalized and a deployment schedule starting June 15 was set (day after the Hood Canal bridge re-opens). Aaron Wech completed automating his tremor location routine and set up an Interactive Auto-Tremor Map.
• March, 2009 - Planning for array locations has been underway since last fall. Several siting trips have been taken and preliminary sites have been chosen for seven possible sites. Permitting is under way for the use of these sites.
• March 4, 2009 - A new special tremor page is started for the expected ETS of summer 2009 and for the AofA experiment. (Some linked web pages are not yet functional for the coming ETS but will be by this summer).

BACKGROUND INFORMATION

Using stations from the PNSN and the USArray Transportable Stations (TA) we use a semi-automated processing system to track the general occurence of where and when deep tremor takes place.

As in the past we plan to collaborate closely with the seismologists and geodesists of the Pacific Geoscience Centre (Natural Resources Canada) and Central Washington University to follow the development of the next ETS.

Previous Studies of ETS by UW scientists

• 2003 Deep Tremor - Observed by scientists at the UW
• 2004 Deep Tremor - Two tremor episodes, one in May in the central Puget Sound and one in July in northern Puget Sound - Vancouver Island.
• Summer of 2005 Deep Tremor Study
• Fall-winter of 2006-07 Deep Tremor Study
• Winter of 2008 Deep Tremor and CAFE experiment

Other information about ETS

• Slow slip events and episodic tremor - from the Pacific Geoscience Centre of the Geological Survey of Canada.
  Note that the PGC provides a very nice near realtime plot of key GPS stations for tracking motions during the next ETS.
• Geodesy and Slow Earthquakes from the Geodesy Labs of Central Washington University.
  You can find sliding three year windows of daily grouped updates of cleaned, detrended GPS components for all of western North America. Probably the most interesting ones for the 14 month ETS are the longitude components of BC.Cordillera Region and the WA, Olympic Peninsula region though there are others here that show changes as well.
• Borehole strain meter data from the Plate Boundary Observatory (PBO) are available in near real-time.
• Processed PBO Borehole Strain meter data by John Langbein (USGS) to detect rate changes.

Acknowledgments

• Steve Malone of UW maintains this blog
• Tony Qamar of UW wrote the original tremor envelope plotting software
• Ken Creager and Aaron Wech of UW provide the cross-correlation location plots
• Bob Crosson of UW provide envelope functions from which cross-correlations are done.
• Aaron Wech has developed the automatic cross-correlation, tremor location processing routines.
• Garry Rogers of PGC provides routine update information on tremor observed in Canada
• Herb Dragert of PGC provides analysis plots of GPS data
• Tim Melbourne of CWU provides analysis and plots of GPS and long baseline tilt-meters data.
• Honn Kao of PGC provides routine tremor analysis for Canadian stations.
• Evelyn Roeloffs and Wendy McCausland of USGS provides analsyis of borehole strain meter data
• John Langbein of USGS provides strain meter analysis plots.
• USArray and Plate Boundary Observatory of EarthScope provide all sorts of data

Financial Support

• Routine operations of the Pacific Northwest Seismic Network is supported by a cooperative agreement from the US Geological Survey, a contract from the Battelle Pacific Northwest Laboratory, and funding from the State of Washington and the School of Arts and Sciences of the University of Washington.
• Special funding for deep tremor studies has been made available from EAR-Geophysics of the National Science Foundation and from EAR-EarthScope Science of the National Science Foundation.
• The CAFE experiment PIs are: Ken Creager, Geoff Abers, Steve Malone, Stephane Rondenay, Brad Hacker and Tim Melbourne and is supported by the National Science Foundation.