...... PNSN ETS HISTORICAL RECORD

Summer 2005 ETS

Deep Tremor in Cascadia Zone - Special Seismic and Geodetic studies
Sept. 6-30, Summer, 2005

This ETS is over. There is a new set of pages for the fall 2006 ETS.

This page will have frequent updates from observations and studies of Cascadia deep tremor expected during the late summer and early fall of 2005. News will be posted (latest at the top) and figures from time to time.

NEWS (latest at the top)

• Sep 30, 2005 - Garry Rogers of PGC reports that the ETS seems over. In the past 48 hours there was only 6 hours that contained any tremor and that was very weak. The last few tremors emanated from a region just west of Port Alberni.
• Sep 26, 2005 - Garry Rogers of PGC reports that the ETS event continues and continues to migrate northwest along Vancouver Island. Present tremor activity is now north of Alberni Inlet in central Vancouver Island but has dropped in intensity and volume over the weekend.
• Sep 22, 2005 - Garry Rogers of PGC reports that some strong tremor bursts and frequent milder ones are continuing in southern to central Vancouver Island in the Cowichan Lake region northwest of Victoria.
• Sep 20, 2005 - Very little tremor is seen in Puget Sound area over the past few days and most of this is probably coming from sources to the north. Dan Johnson of UPS reports that Puget Sound/Olympic Peninsula GPS stations stopped moving as of a few days ago. Motion on southern Puget Sound station was not observed at all during this ETS. His portable instruments will be left out for another month to six weeks to make sure there is a good baseline for after the event. At this point it seems that the ETS has moved totally on to Canada and theUS part of it is over.
• Sep 18, 2005 - Tremor has become weaker on Washington stations and only is obvous for limited periods on the most northerly ones. Garry Rogers of PGC reports that the tremor continues on Vancouver Island with some very strong periods showing up well north of Vicotria.
• Sep 15, 2005 - Tremor in Washington has decreased in duration and intensity over the past couple of days as the ETS event moves north on Vancouver Island as expected. Garry Rogers of PGC reports that tremor on Southern Vancouver Island is a bit lower than before (only 8 hours of last 24) but s centered under souther Vancouver Island. Herb Dragert documuments as much as 4-5mm of westward motion at northern Olympic/Southern Vancouver Island GPS sites.
• Sep 14, 2005 - Press release from the PGC of the Geological Survey of Canada issued.
• Sep 13, 2005 - Herb Dragert of PGC reported last night that westward motion of selected sites on southern Vancouver Island (ALBH, BCES, PGC5) and northern Puget Sound (SCO2,SCO3) are confirmed. Dan Johnson of UPS adds that there is no motion within the Puget Sound area south of about 47.7N. John Cassidy of PGC reports that tremor has picked up over the past several days in southern Vancouver Island with some being observed as far north as Nanaimo. Tremor on PNSN stations indicate that it may also have spread a bit to the south. Periods of very strong tremor are observed on station HDW.
• Sep 12, 2005 - Strong tremor in northern Puget Sound and some to the south also. Tentative confirmation of GPS signals from several sites in northern Puget Sound were provided by Dan Johnson of UPS for stations SCO3, WHD2. He reports that the beginning of the ETS geodetic signal may have been as early as Sep 7 though it takes at least four or five days to resolve the change.
• Sep 11, 2005 - As of the earliest hours of September 10th, the tremor is now strong during most hours. Still no GPS confirmation.
• Sep 9, 2005 - Tremor has continues and is almost constant but still at a very low level and occasional periods of stronger tremor. No GPS confirmation yet.
• Sep 6, 2005 - Tremor has continued and increased in amplitude and duration on Sep 5 and 6. The tremor seem to be occuring in the northern Olympic Penninsula- Strait of Juan de Fuca region. Tremor has also been noticed on the southern most station of the PGC.
• Sep 4, 2005 - Brief bursts of tremor were seen on stations in the central Puget Sound on Sep 3 and 4th. There were five bursts of 10-20 minutes each on Sep 3 and three similar length but slightly stronger bursts on Sep 4.
• Aug 22, 2005 - Both today and on Aug 19 there were bursts of tremor from Northern California (general Lake Shasta area). California data is only reviewed once a week and because of field work I was more than a week behind. Nine hours on Aug 19 had tremor bursts from 5 to 45 minutes long. Twelve hours on Aug 22 had tremor bursts from 5 to 55 minutes long. This tremor is apparently NOT related to that in northern Oregon and Washington.
• Aug 14, 2005 - Early this morning there was about 20 minutes of very low level tremor from the south Puget Sound area; not likely the beginning of anything big.
• Aug 13, 2005 - Installation of the seismic array just south of Port Angeles was completed today. The array, which involves a total of 11 EarthScope Flexible Array seismometers from the IRIS PASSCAL instrument center, is comprised of 6 short-period 40T's and 5 broadband 3T's with an average spacing of 500 meters between the short-period instruments and 2200 meters between broadband stations.
• Aug 8, 2005 - Dan Johnson reports that 10 GPS stations have been successfully installed in the Olympics with another 8 to be done in the next few days. The seismic array siting has been done near Port Angeles with installation to take place by the end of this week. No tremor has been observed from northern California to Northern Washington yet.
• Aug 2, 2005 - The campaign GPS deployment to monitor the upcoming Cascadia Episodic Tremor and Slip event is underway, with the first 3 of an expected 30 stations installed on 2 August in the western Olympic Peninsula. The photo of installing a GPS station, (OL11) above Clallam Bay shows PI Dan Johnson of UW, University of Puget Sound undergraduate field assistant Nick Carman, and UNAVCO Facility Project Engineer Nicole Feldl.
• July 26, 2005 - Seismic instruments from the USArray (flexible component) arrive at the UW from the PASSCAL instrument center. Unpacking and initial testing of these instruments begin. Several siting trips to the field site have already been made for preliminary work.

BACKGROUND INFORMATION

In anticipation of a main ETS event taking place sometime between Aug and Oct, 2005 the PNSN has requested seismic instruments from the flexible array of NSF's EarthScope program to install in the northern Olympic Peninsula. These instruments will be installed in a combination of array configuration and distributed network configuration in the Sequim-Port Angeles area. A small NSF grant has been awarded to help with the logistics of these installations. Combined with the regular seismic stations of the PNSN, strain and seismic stations of the Plate Boundary Observatory (PBO) and the PANGA array, and the Pacific Geoscience Centre we should get some very high quality data from this expected ETS.