The Applicability of Seismic Refraction Soundings in Permafrost Near Thule, Greenland

Book excerpt: The applicability of the seismic refraction method for engineering purposes was investigated in the Thule area of Greenland. Special attention was given to the cases in which shallow ice overlies frozen ground and in which frozen glacial drift up to a few hundred feet thick overlies bedrock. Seismic velocities were measured in different types of sediments of the Thule formation and in the crystalline basement rock. The velocities in rock and frozen ground were generally high, cementation by ice being the most likely reason at the relatively low ground temperatures of about -10 C. It was found that, with comparable velocity discrimination, the refraction method gives more complete information in permafrost than in unfrozen material, since later seismic events can be identified on the records shortly after the first arrival. Later events also made wide angle reflection soundings possible at a depth as shallow as 200 ft. A nagative velocity gradient in the frozen ground is believed to be responsible for the rapid attenuation of tthe direct wave. (Author).