Installing a "Cold and Dark" Seismic Station in the Yukon using a Trillium 120 Posthole
Installing a "Cold and Dark" Seismic Station in the Yukon
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A three-man team from the EarthScope Transportable Array and IRIS/PASSCAL installed a prototype "cold and dark" seismic station at Eagle Plains, Yukon Territory, Canada, just 30km south of the Arctic Circle from October 8-13, 2012. The station installation developed new methodologies for drilling a shallow, 55" deep borehole in exposed bedrock. Protection for electronics, power, and communication subsystems (from the elements, and from large wildlife) was provided by an all-weather hut bolted to bedrock.
The late-season install required 2 days of driving north from Whitehorse, Canada, along the Dempster Highway. Eagle Plains is a remote outpost in the wilderness, consisting of a hotel and diesel repair facilities for truckers and tourists stranded by bad weather. Temperatures on-site rarely rose above 10oF, but the long nights provided many opportunities to observe magnificent aurora borealis.
One day was spent preparing the site and drilling the sensor borehole using core drilling equipment designed for concrete work. A Multiwave Azimuth Pointing System using differential GPS allowed for the Nanometrics 120PH borehole broadband seismometer to be correctly oriented at depth. An onboard, self-leveling gimbal system provided final leveling for the seismometer.
Site preparation took just over four hours; two hours of this time was spent waiting for the drill's anchor epoxy to cure. The actual drilling time was 57 minutes, at a rate of 1"/min. The rate would be less for non-eroded igneous or metamorphic rock. Much more time was spent removing the cores than for the actual drilling. When the drilling was finished, the rig was packed away, and the borehole was ready for sand and the sensor.
Once the sensor was placed down the borehole, fiberglass insulation was added, and the hole was covered with a concrete cap. Data transmission is via FreeWave RF radio to the nearby settlement, and from there, a dedicated DSL line over microwave link inserts the waveform data into the internet.
The final phase of construction was installing the hut. Bolted to bedrock and populated with over 500 lbs of batteries and electronics, the hut is intended to provide protection from curious bears, heavy snow and high winds. A GPS antenna and a weather station were bolted to the outside of the hut.
Upon completion of the installation, the team heads back home via the Dempster Highway, made infamous by the TV series "Ice Road Truckers." The station equipment was purchased by the Yukon Territory Geological Service, and was installed by TA and PASSCAL staff.
Jun 27, 2013