• May 12, 2008 - The tremor has moved to along the north coast of the Olympic Peninsular as determined by the automatic locations. Amplitudes are consistently lower on southern Sound stations and higher in the north. A short animated film clip shows the time progression of tremor locations over the past couple of weeks. Note that there is a early burst of tremor in the northern Sound on Apr 23-25. This is not seen on a signal amplitude plot starting on Apr. 28 that shows the earlyest tremor on HDW starting about Apr. 30 but really picking up on May 2 while again decreasing starting on May 9.
• May 10, 2008 - The tremor is definitely moving north. Yesterday Garry Rogers of the PGC reported that "the tremor from beneath the Olympic Mts in Washington is starting to show up on the southernmost Vancouver Island seismographs. Since yesterday afternoon (0200 Z May 9) at least to 2200Z ther have been 11 hours containing tremor activity, all coming from south of Vancouver Island". Herb Dragert of PGC reports that there are no GPS signals yet indicating the detection of slip.
  The Big Skidder Texan array was serviced yesterday while the tremor locations seem to be slightly to the northwest. From the autolocations the tremor is definitely spread out over a larger area than it was a few days ago.
• May 8, 2008 - The tremor is really ripping over the last few days with most hours having moderate to strong tremor that is showing on many stations. According to Aaron's automatic tremor loation plots tremor seem to have started moving to the northwest and is now directly under the herd of Texans at the Big Skidder site. Justin has scheduled a service run for these 80 stations on Friday.
• May 5, 2008 - News Flash! Tremor has really picked up. Jenny Hanna reports 15 or more hours of tremor per day during each of the last three days from analyzing the detailed May, 2008 envelope plots. Is this the start of the 2008 ETS event????? Wech's automatic tremor locator has recently gone through a thorough tuning process and is tracking tremor day-by-day showing strong tremor the last few days under Hood canal. The UW crew lead by Justin Sweet deployed about 80 "Texans" today in a small-aperture array on the Olympic Peninsula to record all this activity with high fidelity.
• May 2, 2008 - Low-level tremor continues off and on since Apr 30 in the south Sound area; easily seen on HDW and weakly seen on a few other stations.
• Apr 30, 2008 - After no tremor since Apr 23 we have had low level tremor again back in the south Sound area from 02:00Z off and on until at least 20:00 today.
• Apr 24, 2008 - Suddenly, after weeks of almost no tremor in Washington, there were several hours of moderate tremor yesterday, the strongest occurring around 16:30Z. Thanks for the early heads up by Wendy McCausland. The tremor seems to be located in the north Puget Sound between the Olympics and San Juan Islands. By 20:00Z it had died out and up until 22:00Z today there doesn't seem to be much more if any. Is this just a teaser for things to come or a typical "burble" that happenes from time to time unrelated to a real ETS?
• Apr 4, 2008 - It has been very quite around here. No tremor in Washington for several weeks. However the PGC dudes (Honn Kao, Garry Rogers, Herb Dragert) report fairly strong tremor in the north Vancouver Island area lasting for four days and then quiting yesterday and without any detectable GPS motions. Maybe that section is mimicing the southern Puget Sound section and "faking" and ETS event starting.
• Mar 12, 2008 - No tremor for the past three days. A 21 day seismic envelope plot of the period Feb 28 to Mar 12, 2008 shows the 7+ days of tremor that looked to be the beginning of an ETS. Note that it is quite strong on HDW but not nearly as obvious on the nearby stations, CPW, SMW and GNW though it can be seen above the noise there too. Other noises showing up on many stations are obviously diurnal cultural noises that even are lower levels on weekends. The Auto-Tremor Map for the past few days shows almost no tremor locations.
• Mar 9, 2008 - After some very strong tremor on Mar 7 tremor seems to have decreased during Mar 8. Over the past 24 hours (Mar 9 GMT) there has only been very weak tremor now and then. It seems that the ETS has either stalled or this is not the main event. As previously scheduled the almost 90 Texan seismographs in the Olympics were serviced, swapping existing ones for new ones.
• Mar 7, 2008 - Tremor continues at moderate to strong levels during periods over the past two days but does not seem to have moved from its position in southern Puget Sound. Tim Melbourne from Central Washington University reports that no anamolous tilt is being observed on a long baseline tilt meter located at Shelton. Herb Dragert of Pacific Geoscience Centre reports that the GPS network of stations in the region are NOT showing any lateral motions consistent with an ETS. However, Wendy McCausland and Evelyn Roeloffs of the Cascade Volcano Observatory report that their analysis of the PBO borehole strain meter B018 (south of Olympia) does show a subtle signal that may be the beginning of an anamolous strain event.
• Mar 5, 2008 - Tremor is continuing at moderate levels but variable at different times. 90 high-frequency verticals (Texans) were installed today in a tight array in the central Olympics with the hope that the tremor will soon move north west right under the array. TA site, C04A has had an autonomous broad-band instrument installed. The experimental automatic tremor location routine by Aaron Wech is plotting contours of number of locations per area and shows where tremor is currently concentrated.
• Mar 4, 2008 - Tremor continues today at similar levels. A large crew is headed to the field tomorrow to deploy a heard of Texans. A CAFE station is being moved to the abandoned TA site of C04A to run autonomously for at least a month. The automatic tremor locator process is being updated with some improvements but is not yet plotting correctly. With everyone in the field tomorrow it will not be fixed until Thursday. A simple press release announcing the ETS start is being prepared.
• Mar 3, 2008 - Tremor has been detected in the South Puget Sound area starting yesterday (Mar 2). It is moderately strong on station HDW from time to time but quite weak on most other stations in the area. Unfortunately a key TA station C04A was removed a couple of weeks ago and thus is no longer available for detecting tremor. The CAFE autonomous stations were all serviced over the past two weeks and so should be working fine now. Plans are being made to do the installation of a many component array of high-frequency, vertical only sensors (Texans) at the Big Skidder site on Wednesday, Mar 5.
  An experimental auto-locator for tremor is being developed by Aaron Wech. While only in the early testing mode we are putting up its results on this web page as of today.
• Feb 25, 2008 - No ETS starting yet. Unfortunately, the USArray has been pulling stations out of western Washington to move to their next deployment much farther east. This and some heavy snow conditions causing other station failures has reduced the number of good stations for studying the next ETS. However, the Texan array deployment project is just about ready to go. Most instrument sites have been found and marked so when tremor starts we should be able to deploy most instruments in a very short time.
• Feb 7, 2008 - No obvious tremor for the past week or so. The second half of Feb 5 looks like it might be tremor on the RMS-RSAM plots but while the over all envelope rises slowly and falls together on several stations the short term (minutes to tens of minutes) details don't match. This pattern is consistent with general wind noise due to a storm. For much higher details we are now providing large PDF files of hourly envelopes for February, 2008 and for March, 2008. April, 2008. May, 2008.
• Feb 1, 2008 - The semi-realtime seismic amplitude (envelope) plots have been started again and should automatically update every hour or so. You will find these at: RMS-RSAM Envelope Plots.
• Jan 31, 2008 - A whole herd of Texans (RT125) have arrived at the PNSN labs. The PASSCAL expert, Steve Alzevedo is training a group of us to configure and operate the Texans. A siting trip will be made within the next week or so.
• Jan 29, 2008 - Again yesterday there were several hours with moderate tremor in the central Puget Sound. It seems that there will be several quiet days and then a day with some activity, but not enough to indicate a major ETS is underway. A simple plot of hours per day with tremor since the beginning of 2008 shows a few such peaks. An explanation of our current analysis process and a summary of 2007 activity is available under a Tremor Tracking Page.
• Jan 14, 2008 - During yesterday and today several hours of weak to moderate tremor was observed, mostly in the north Puget Sound region.
• Jan 10, 2008 - Discussions within the PNSN scientists are centering around doing a prototype experiment this winter using a bunch (~100) Reftek-Texan recorders in a very dense array to look for P-wave coherence from deep tremor. This experiment will be used to see if it is worth using these short-period, vertical-component only in a much larger experiment during the following ETS. Disccusions with PASSCAL indicate that we could get a set of Texans by the end of January, in time to deploy just as we first detect the arrival of the next ETS. These units will be run in continuous mode for one, two or three four day periods during the strongest tremor. They will be installed at or around the Big Skidder array site where there are 6 three-component instruments currently running.
• Jan 8, 2008 - New Tremor page started for the expected ETS of winter, 2008. According to Herb Dragert of PGC and based on his average GPS start-time interval for the 14 month ETS events of 450 days the estimated start time on southern Vancouver Island would be Apr 24, 2008 +/- 76 days. Since there may be a tendency for a long interval (previous interval was 506 days) to be followed by a shorter interval and the tremor often starts in Puget Sound area before Vancouver Island he estimates it could start as early as mid February.

BACKGROUND INFORMATION

Using stations from the PNSN and the 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

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.