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Construction of an Unattended Seismological Observatory (USO) in Permafrost
COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
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The construction of a large diameter cased borehole and surface instrument shelter for the installation of a high resolution, long term recording seismograph in marginal permafrost 15 miles west of Fairbanks, Alaska, is described. Permafrost extended to a depth of 123 ft and consisted of frozen silt, peat and sandy small gravel and was underlain by a thawed gravel aquifer. The first 48 ft of 16-in. hole was drilled with a truck-mounted auger. Forty thermocouples were installed in the fill placed over the casing and in the ground beneath to monitor thermal behavior. Data from these are discussed. Five thermistors attached to the borehole package yielded data on the ground temperature at the 80 to 85-ft depth interval. Using these data, the permafrost thickness obtained by exploratory drilling, and the mean annual air temperature, the ground temperature profile at depth is estimated.
APPROVED FOR PUBLIC RELEASE