...... PNSN ETS HISTORICAL RECORD

Summer 2010 ETS

Deep Tremor in Cascadia - a continuation of Array of Array experiment
March, 2010- .... (Summer 2010)

We will update this page with information, observations and studies of Cascadia deep tremor expected during the summer of 2010. The Array of Array experiment is a follow up to the CAFE experiment of the previous few years that explicitly uses up to eight arrays of 20-40 seismometers each in the northern Olympic Peninsula to study the ETS tremor as it moves under this region. News will be posted on this page (latest at the top) and references to figures from time to time.

There is a map of AofA installed stations for operation during the expected ETS period.

NEWS (latest at the top)

• Sep 20, 2010 - Very little tremor in northern Cascadia since the ETS ended on Sep 8, but there have been moderate burbles of tremor in southern Cascadia since then extending from just south of Roseburg to near Redding, CA. While very noticable this tremor does not seem to be continuous enough in time or space to be a real ETS. Processing of the AofA data recovered recently is going smoothly with the first array being loaded into a Winston waveserver right now. We hope to have a few example plots to display soon. In the mean time there is a summary of spectrogram plots that cover he whole period for station HDW (best response to ETS tremor) and sample times at a few other stations.
• Sep 16, 2010 - A massive effort took place over the past couple of days to get all rt-130, three-component stations serviced to collect all the data during the ETS. The story goes that Justin, il Capo di tutti capi serviced 26 stations in one day, half of them with no GPS to help find them. All flash cards are back in the lab and the down-loading, processing has begun. A better story was Abhi getting locked behind a logging gate in the rain with no cell recpetion for a few hours before hiking far enough to be able to contact someone to rescue him. Data downloading and processing will take many days to complete before we will have a good picture how good (or bad) the data are.
• Sep 12, 2010 - Oh dear. Is it really over? No tremor in the north but in the past two days there has been renewed activity at the south end of the ETS zone, two sets of burbles just north and south of Longview. I am going to again call it "after-tremor".
• Sep 10, 2010 - There was just a bit over an hour of tremor along the west side of Vancouver Island today; an "after-tremor". I think that this doesn't change the ending time of the latest ETS of Sep 8. In the meantime a few changes of possile interest to others is underway. Dr. Wech of the famous wech-o-meter is preparing to leave for a post-doc in New Zealand. As a parting gesture of good will he has added a feature to the Interactive Tremor Map (AKA the "wech-o-meter) to allow anyone to download selections from the tremor catalog for their own use. Cool! He also has added some pull-down menus to help find additional information or explanations. The operation of this system has been ported to one of the PNSN's product generating computers and the maintenance of the system is being turned over to PNSN staff (ie ex-professor, ex-director, ex-seismologist, retired, goof-off, but blogger extraordinaire S. Malone).
• Sep 9, 2010 - No tremor today anywhere so this ETS is over.... even if there are a few burbles over the next few days a break in the activity indicates this one is done. Thus this ETS lasted exactly one month and extended from Longview in southern Washington almost to Port Alberni on Vancouver Island, a distance along strike of about 360km.
• Sep 8, 2010 - END OF ETS During the last two days the tremor has decreased in intensity a lot. It seems to be down to only one quarter as many locatable bursts in the north and today there were none in the south near Longview. So maybe this ETS is over.
• Sep 6, 2010 - This ETS seems to still be going on as strong or stronger than most. Strong and lengthy tremor continues to move slowly north on Vancouver Island almost reaching the Port Alberni area. The southern batch keeps moving south, now concentrated under Longview, WA. A report from Tim Melbourne of Central Washington University confirms this seismologist's suspicion that geodetic motions seem bigger than many ETS in the past. He thinks motions are on average 40% larger than seen in previous ETS including detectable uplift to the west of mapped tremor locations. Also his "Long Baseline Tilt meters show a beautiful recording (praise be summer weather), maybe 350nr of total tilt, and interesting time dependence." In another week or so some calculated slip models should be available.
• Sep 4, 2010 - The AofA experiment is over but this ETS continues with lots of very strong tremor on Vancouver Island and a continuing but weaker batch to the south nearing the Washington-Oregon border. While no experts have sent us any specific information even a seismologist can see substatial motions on many of the GPS instruments in and around the Olympics processed at Central Washington University. It seems that even instruments out near the coast are showing significant motion.
• Sep 2, 2010 - All Texans have been recovered and all their data off-loaded and stored safely. The post processing will be run on it shortly and then it will be loaded into a Winston waveserver for access by the experiment team. Still no specific plan for servicing the rt-130 three-component stations. AND, the ETS continues. Today was an active time in southern Vancouver Island with a second batch of tremor farther north just west of Nanaimo. Also, after a day's break the southern batch of tremor reapeared between Centralia and Longview. We have had no word from any of the geodetic lookers (GPS, strain, tilt) since very early in this ETS but assume that this ETS has a geodetic signal at least as significant as previous ones.
• Sep 1, 2010 - While the ETS seems to be continuing with tremor moving NW on Vancouver Island it is now far enough from the AofA to call this experiment over. The RT-125s (Texans) were removed from four of the arrays today and the remaining two arrays will be stripped of their Texans tomorrow.
• Aug 30, 2009 - Today was the last day for regular servicing of the Texans. However, since a big rain is forecast for tomorrow we decided to let them all go one extra day and not start the pull out until Wednesday. They all should have batteries to keep clocks going until at least Thur even if they stop recording on Wednesday morning. Tremor continues on Vancouver Island; with most of it quite a bit north-west of Victoria. However there was a small burst yesterday evening near Sooke on the south coast that might be recordable on the AofA.
• Aug 29, 2009 - The tremor continues to move noth (and the southern batch to move south). Today the souther edge of the main tremor batch was a far away from the AoA arrays as when the whole thing started almost three weeks ago. Thus, it is well outside the region where the AofA can record it well. So, we will do one more Texan exchange tomorrow and then pull them all out of the field on Tuesday and Wednesday. We will wait at least a few more days to a week before we do a full service run of the RT-130s.
• Aug 25, 2010 - Most of the tremor is now north and west of the AoA experiment and thus we are starting to talk about when to pull the plug on the Texans (which take daily diaper changes). To help we have produced a set of comparative tremor plot maps for the most recent 4 ETS broken down by weeks. The last column is for the current ETS and will be updated with another week in a few days. Anyone care to guess when we can figure this puppy is too far away to be seen by Texans?
• Aug 24, 2010 - The main ETS tremor is now on southern Vancouver Island but with a persistent patch continuing just south of Olympia. However, the total number of tremor locations by the wech-o-meter is down quite a bit compared to the past week or so. The AofA team has switched with John and Steve returning to Seattle and Ken and Heidi talking over doing the servicing. Reviewing the course of the tremor associated with this ETS it seems to be following very closely the previous two ETS. At this rate it will be over in about 7-10 days.
• Aug 22, 2010 - Yikes! Lots of Cascadia is lighting up with tremor today. The main ETS patch is now straddling the Straits (Honn's TAMS system using only Canadian data has been reporting tremor being seen on southern Vancouver Island stations for a few days). The patch of tremor just south of Olympia continues. There is a new patch just south of Portland and a burble in southern Oregon. What the heck is going on? Time will tell.
• Aug 21, 2010 - The main ETS tremor is now located in the middle of the Straits of Juan de Fuca with the leading edge under Victoria. The Canadians must be happy now. There also continues to be a separate persistent patch of tremor near Olympia that seems to be slowly spreading south with its leading edge near Centralia. Do we have a double ETS this time? Time will tell.
• Aug 20, 2010 - Watch out Candians, the tremor is now on your door step. Several wech-o-meter locations this evening are just outside Victoria harbor. By tomorrow Dr. "ETS" Dragert will have them under his garage.
• Aug 19, 2010 - The tremor continues to slowly move north with the leading edge in the middle of the Straits. On the spectrograms it appears to be getting weaker but that is probably only because the best stations for seeing it without cultural noise are to the south (HDW and DOSE). It is now weakly but clearly seen on MCW and SNB. The leading edge of it should be crossing into Canada in about two days. Tomorrow we will have completed three full service runs of all 8 AofA arrays. Preliminary checks of the data using a couple of small local earthquakes for waveform comparisons indicate that the Texans are doing well. Today a switch was made in crew. Mario La Rocca from Osservatori Vesuviano left after five days of great work to be replaced by the big boss himself, John Vidale.
• Aug 17, 2010 - There seems to have been a bit of a lull in tremor amplitude over much of the last day compared to the previous several days when it was roaring. There is a summary envelop plot of the first 10 days of this ETS that shows the daily fluctuations and recent lull. The northern edge of the tremor is now north of the Olympics coast and there is a southern bunch of tremor clearly separated from the rest, south of Olympia.
• Aug 16, 2010 - The first complete round of servicing of all AofA arrays is now complete and a quick check of a teleseism shows that all data recovered looks Good. So far so good.... The tremor is now located directly under the arrays so this should be fun. Also, Tim Melbourne of CWU reports that preliminary analysis of several GPS sites in southern Puget Sound are now seeing the ETS but need to wait on final orbits to nail down the details. And, Kathleen Hodgkinson of UNAVCO confirms that several strain meters are showing well resolved ETS signals and she provides a summary plot of the obvious ones.
• Aug 15, 2010 - The northern edge of the tremor has reached the Array of Arrays, so good data should be being recorded right now. Some of the tremor locations are right under the AofA team's motel in Sequim (but we are feeling nothing). Here is hoping that everything is working well. The Canadians should soon be seeing it coming at them from the south. There is still a pocket of tremor south near Shelton so it is quite spread out now.
• Aug 14, 2010 - Tremor continues as before with a hint it is bifurcating into a cluster southwest of where it started (now its just east of Shelton) and then a more dispersed patch moving into the eastern Olympic Mountains. The northern edge of this patch is very near the location of our BS array. There is a summary map from the wech-o-meter showing the first week's progression of tremor color coded by time.
• Aug 13, 2010 - The tremor is again moving to the northwest. Comparing the northern edge of it now compared to on Aug 8 it has moved about 35km in 6 days even though the center of each day's locations has moved less than that (~15 km to the west). It remains as strong as ever with some strong bursts showing clearly on stations in the Cascades and San Jaun Islands. At the AofA site the first service run for the two most easterly arrays was completed today but there is no report yet on the nature of the recorded data.
• Aug 12, 2010 - After moving slightly to the northwest over the past few days the tremor seems to have moved back to near where it started or even slightly to the south. Uhmmm. What is going on here? On the slip side Evelyn Roeloffs points out that one strain meter, B018 has a clear change from its background starting on Aug 8.
• Aug 11, 2010 - Tremor continues similar to yesterday. The AofA team completed densifying the 8 arrays and will take a day off to get the servicing schedule in a sequence where two arrays wil be serviced each day in a four day rotation.
• Aug 10, 2010 - Tremor is even stronger today with over 18 hours reported by the Wech-o-meter. There is also evidence that it is starting to slowly move north but is still mostly in the central to southern Puget Sound. Evelyn Roeloffs reports that the PBO strain meters in the region seem very stable for the past few weeks and so are well poised for recording this ETS without unusual artifacts. She also reports a possible beginning of a small extentional strain on B018. Today two AofA field teams installed 10 Texans in each of the four most easterly arrays (BS, CL, GC, TB). A UW Press Release about the ETS start and the AofA experiment was released today.
• Aug 9, 2010 - The southern Puget Sound tremor bursts got stronger and longer today and thus we are declaring that this is the beginning of the next ETS (at least until it goes away). Two AofA teams, led by il capo di tutti capi, Justin are leaving first ferry in the morning to add ten Texans to each array over the next two days.
• Aug 8, 2010 : ETS START - About 5 hours of fairly weak tremor was seen today located in the south Sound area near where previous ETS start. This seems a bit too far east but if it continues for most of another day we will probably begin the installation trip for Texans (Reftek RT-125 single component, highly portable seismograph) to densify the already installed arrays.
• Jul 27,2010 - Only a small burble of tremor in our part of the world on July 25 but not enough to get excited about. A final field trip of two crews will do a final check of all AofA sites within the next couple of days.
• Jul 1, 2010 - It has been very quiet over the past month; a few days of tremor in northern California. Additional preparations have been made for the AofA experiment. A crew of 6 people spent three days doing some minor repairs, some station relocations and some surveying for Texan sites at Lost Cause (LC). Also, all of the AoA data collected thus far has been loaded on a Winston wave-server for easy access. We are ready so bring it on.
• Jun 1, 2010 - A few days of tremor took place in western Washington from May 27-31, starting south of Olympia and ending in central Puget Sound. This does not appear to be an early ETS but we are watching things closely.
  Evelyn Roeloffs reports that: It looks like a small strain excursion started about May 29 at B018. Easiest place to see it is on the processed plots that Kathleen Hodgkinson posts on the UNAVCO website (NO LONGER AVAILABLE). The meaningful ones are the "shears" 2Ene and Eee-eNN.
• May 27, 2010 - Little tremor anywhere in Cascadia over the past month. A couple of tasks have been completed. Aaron has streamlined the Interactive Tremor maps so that they work much faster by storing the tremor catalog in a database and querying that to get subsets. Also, three different trips were made to the AofA sites to do service runs and restart those arrays that were shut down for the middle of the winter. As of today all rt130s at all of the arrays are operating other than one or two at each array that have hardware problems. We are in the process of down loading and processing data for a period in mid March when there was local strong tremor.
• Apr 28, 2010 - The realtime RMS-plots have been restarted again to show the average envelope level of filtered data at a few key stations. These plots, unfortunately also commonly show variations in background noise levels and thus are harder to interpret that we would hope.
• Apr 12, 2010 - Little tremor anywhere these days. But, one of our up and coming star grad-students (try to take some glory from Wech), Abhijit Ghosh has a nice page illustrating array processing of 2008 ETS tremor from one seismic array. Check it out. He is starting to work doing the same sort of thing from preliminary data from the Array of Array experiment.
• Apr 6, 2010 - Some northern California tremor these days but nothing much in the north of Cascadia.
• Mar 29, 2010 - Tremor is back in the southern Vancouver Island area. For the past four days there has been increasing amounts of tremor just north-west of PGC. What are those dudes doing?
• Mar 25, 2010 - Wech has done it again; a new and improved NEAR Realtime Tremor Map that runs hourly and shows the "possible" most recent tremor locations. One can turn on the cluster selection part of his location routine (more likely to be real tremor locations) or turn it off to see everything that gets located even if it may not be tremor. The map also includes black triangles showing the location of the AoA arrays. What a guy. Will he ever stop improving this and finish his dissertation?
• Mar. 24, 2010 - No tremor in Washington now. Diagnostic spectrograms plots show color intensity as a function of frequency. For stations HDW and B001 in particular tremor will show up as bright spots in the 2-6 Hz range.
• Mar. 20, 2010 - It seems that the tremor reported two days ago was indeed an inter-ETS burst. By today the north-easter Olympics tremor had mostly died out. The AoA crew was starting to gear up to head for the field tomorrow but by evening had decided to cancel. The Texans have been ordered to stand down. There is a map of north-east Olympics for Mar 16-19 showing the located events during this mini-tremor burst.
• Mar 18, 2010 - Oh dear, we have had three days of tremor in the northeast Olympic Peninsula area as reported by the Wech-o-meter and confirmed by TAMS. Today's lasted for 8 hours. This is too early for it to be the regular 14 month major ETS....... we hope. The locations seem to be on the eastern edge (down-dip) of the usual area for major ETS tremor and so the hope is this is a strong chunk of "inter-ETS" tremor and it will go away in a couple of days.
• Mar 11, 2010 - After several days of seeing no tremor from the recent sequence on Vancouver Island I think we can consider it over. The last minor tremor seems to have occurred on Mar. 8. Now we wait for something new.
• Mar. 4, 2010 - It should be noted that the ETS that started about Feb 20 in south-central Vancouver Island seems to be still going but perhaps weaker and has moved north. Herb Dragert reports about 3mm of western motion at their coastal GPS stations. Several PBO strain sites (particularly B012) show a very strong signal starting about Feb 22-23. Ongoing processed strain data is updated by Langbein of USGS Menlo Park.
• Mar. 3, 2010 - In trying to get the current best estimated time for the next ETS this blogger querried that most famous of ETS prognosticators, H. Dragert (semi-official ETS consultant to the gold medal Canadian hockey team) who reported:
  A regression of the start times of tremors as recorded by the Canadian Seismic Network over the past 18 years suggests the next one will pass beneath Juan de Fuca Strait on August 14 plus or minus 29 days (standard error of residuals about our linear fit and not a 95% confidence interval).
  He also provides a caveat about a break in the pattern going back more than 18 years but mumbles about a "system reset" back then and thus suggesting that the last 18 years are the ones to use. If this is correct then given that recent ETSs have recently started in southern Puget Sound about 10 days before it emigrates to Canada, then its earliest appearance should not be before about the first week of July. The AofA team will be ready to react instantly to anything after mid April.
• Feb. 26, 2010 - Vancouver Island tremor continues but seems to be moving north rather than threatening to come south with an even earlier ETS in northern Washington. Also, final agreement has been made between the PNSN and Natural Resources Canada to share real-time seismic data between a large selection of stations from both arrays for tremor processing. Both tremor detection and location systems will be looking at common data. Thus Honn's TAMS/SSA and Arron's "wech-o-meter" should be reporting pretty much the same thing between 47 and 60 degrees north in Cascadia.
• Feb. 22, 2010 - Honn Kao's TAMS Reports and SSA locations report strong tremor in southern Vancouver Island. Aaron Wech's Interactive tremor map (wech-o-meter) also picks up this tremor activity.
• February, 2010 - After the AofA experiment missed the ETS of last summer we decided to run the basic arrays right on through the next year shutting down half of the arrays for different months to save batteries. As of the end of January they all had been turned back on and (other than a couple of stations that were stolen) are now all running again. We plan on making one service run in early April to check all stations, replace memory chips and be as ready as we can for when the next big ETS starts.

BACKGROUND INFORMATION

In the past using stations from the PNSN and the USArray Transportable Stations (TA) we used a semi-automated processing system to track the general occurence of where and when deep tremor takes place. Starting in the fall of 2009 a completely automated tremor detection and location systems was put on line by Aaron Wech with an Interactive tremor map web interface.

As in the past we 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 maintains this blog
• Tony Qamar wrote the original tremor envelope plotting software
• Ken Creager and Aaron Wech of UW developed the cross-correlation location plots
• Aaron Wech developed and maintains the Interactive Tremor Web pages.
• 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.
• Justin Sweet and Ahbijit Ghosh are the Array of Array field specialists
• Realtime seismic data is primarily from the PNSN but also uses data from the Canadian National Seismograph Network, the Northern California Seismic Network, Pnd the late Boundary Observatory and USArray, both of EarthScope.

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.
• Ken Creager, John Vidale and Heidi Houston are PIs for the Array of Array experiment supported by EarthScope of the National Science Foundation.