Two new stations were deployed this summer in the NWT of
Canada at Sachs Harbour and Paulatuk.
USArray is cooperating with the Global Terrestrial Network for Permafrost to profile soil temperature at stations.
During 2013 the Incorporated Research Institutions for Seismology (IRIS) will begin to deploy seismic stations in Alaska as part of EarthScope’s USArray observatory. EarthScope explores the structure and evolution of the North American continent using continuous recordings from broadband seismometers and strain deformation measured from precision GPS sensors. IRIS is in its 9th year of operating the USArray Transportable Array (TA), which deploys 400 seismic stations in a west-to-east rolling footprint, that has migrated continuously across the lower-48 United States since project began in 2003. To-date over 1,400 individual station sites have been completed. TA stations are sited in a wide variety of settings, typically operate for 2 years or more, and produce extremely high quality data with an average return of over 95%. The IRIS SAGE Proposal, including the redeployment to Alaska through 2018, has been awarded funding for FY14. The final budget for the TA portion is $7.7M. The migrating footprint extending to the eastern seaboard is now complete, and the TA will begin a single footprint deployment to Alaska and the Yukon in FY14.
As outlined by the report and white papers stemming from a recent Alaska-themed workshop, there are numerous well-defined scientific motivations for shifting the TA to Alaska. In concurrence with recommendations contained within the Autonomous Polar Observing Systems Workshop Report, IRIS is enthusiastic about collaboration with members of the Arctic science community during the development and implementation of USArray in Alaska.
The TA stations in Alaska will be arranged in a grid-like pattern with ~85 km spacing (Figure 1), and are planned to cover all of interior Alaska and westernmost Canada, including parts of the Yukon, Northwest Territories, and British Columbia. Installation of ~290 sites is projected to begin in October of 2013 and finish during summer 2015. IRIS is working with the Alaska Regional Network, Alaska Volcano Observatory, and the Alaska Tsunami Warning Seismic System to build on infrastructure associated with earthquake monitoring during this process. All stations are targeted for deployment lasting between 3 and 5 years. Removal of the stations would then commence in May 2017 and be completed by September 2018.
Figure 1: Potential TA Sites in Alaska and NW Canada 11/20/2013 (map links to original PDF)
The configuration of Alaska-deployed stations will require significant modification from the TA’s current station design in order to operate in the challenging conditions of the far northern latitudes (Figure 2). Remote stations will likely be contained in an insulated, above-ground enclosure similar to those developed for EarthScope’s Plate Boundary Observatory (PBO) GPS stations, which already operate in Alaska. This hut will contain a seasonally dependent power system, with an EFOY/methanol fuel setup functioning throughout the winter and a solar power system for use during the summer. Both systems will periodically charge lithium/air cell batteries. The batteries will power a Quanterra Q330 datalogger connected to a three-component broadband seismometer (STS-2 or 2.5, T120PH or T240, CMG-3T, etc.) residing in an augered hole of several meters depth or cored hole directly into bedrock. The standard TA atmospheric sensor package containing a MEMS state-of-health barometer, NCPA infrasound sensor, and SETRA microbarograph will be included with each station. Additional sensors that have been suggested for deployment include a meteorological pack, strong-motion sensor and/or soil temperature profiler. The footprint of each site will be around 10 by 20 feet. Our goal is to maintain near-real time (12-24 hours, many within seconds) state-of-health telemetry via cellular or satellite phone service at some stations, but full data will only be obtained during the (bi-)yearly in-person servicing of stations. With a datalogger capacity of up to 32 GB storage, the stations are capable of maintaining a complete record from a lengthy deployment.
Figure 2: Design schematic of Alaska TA station TOLK
Figure 3: Earthquakes occurring during 1970-2012 for Alaska and vicinity from the AEIC and USGS PDE catalogs. Figure courtesy of Natasha Ruppert, Alaska Earthquake Information Center.
This design of station is currently being tested at station TOLK (Figure 4), located at Toolik Lake Research Station, north of the Arctic Circle. Performance of the station at Toolik Lake has already yielded important findings on how to auger a sensor hole in permafrost to resist the seasonal freeze-thaw cycle and exposed necessary design changes needed in the vault design. Initial measurements of the seismic power-spectra show that the TOLK station is remarkably quiet compared to other Transportable Array stations in the lower-48.
Figure 4: TOLK - exterior (top left), vault interior (top right), sensor hole (bottom right)
In additional to TOLK, in October 2012 four new stations were deployed across Alaska and Yukon in order to evaluate sensor emplacement strategies and winter-time station performance in continued preparation for the USArray TA Alaska deployment. These stations are deployed in a variety of environments and will be analyzed and compared to determine a preferred deployment scheme. Currently all five stations are online and telemetered with data being delivered in real-time and accessible through the IRIS DMS. Station EPYK has been deployed with the support and cooperation of Yukon Geological Survey and Natural Resources Canada.
Current Alaska TA Stations:
A M 4.0 earthquake in the Yukon is recorded at EPYK.
Maps and Resources
Alaska/Canada Seismicity Map by Natasha Ruppert, University of Alaska, Fairbanks
Robert Woodward, USArray Director Telephone: 1-202-682-2220 ext. 206
Bob Busby, Transportable Array Manager Telephone: 1-800-504-0357
In May 2011, NSF-EarthScope held a workshop dedicated to discussing scientific opportunities in Alaska that could be explored specifically with the Transportable Array and Plate Boundary Observatory. White papers and a workshop report highlight the geologic background of Alaska and outline the key questions in solid earth science that can be addressed through EarthScope in Alaska.
In September 2011, NSF-GeoPRISMS held a workshop to determine research focuses in Alaska and coordinate with EarthScope investigators to maximally leverage the planned deployment of EarthScope’s facilities in Alaska.
Plafker, G. and Berg, H.C. (1994) An overview of the geology and tectonic evolution of Alaska, in Plafker, G. and Berg, H.C. (Eds.), The geology of Alaska: Boulder, Colorado, Geol. Soc. of Am., The Geology of North America, v. G1, p. 989-1021. Note: GSA Online Archives only date back to 1995, so this is probably only available in print.
Freymueller, J.T., P.J. Haeussler, R.L. Wesson, and G. Ekstrom (Eds.) (2008), Active Tectonics and Seismic Potential of Alaska, Geophys. Monogr. Ser., vol. 179, 431 pp., doi:10.1029/GM179, AGU, Washington, D. C.
Servicing TOLK, October 2011