Search

Mapping shallow permafrost by electromagnetic induction — Practical considerations

Kawasaki, K. / Osterkamp, T.E.

AbstractThe performance of shallow-sounding, commercial electromagnetic induction (EM) instruments for geotechnical purposes in permafrost regions is evaluated. These instruments are best used in the reconnaissance mode for pre-drilling information. Modeling of temperature-dependent resistivity profiles based on drillhole temperature measurements and water contents measured on drill cuttings indicate that, in the discontinuous permafrost region, ice-rich silt permafrost and massive ground ice are best detected in the winter months (December through March). However, for areas which have significant lateral variations in soil types or ice content, the late summer or the early autumn months appear to be the best period for detecting ice-rich permafrost, although the resistivity contrast between frozen and unfrozen zones would be relatively large throughout the year. Modeling also indicates that surface moisture in the active layer overlying permafrost can produce apparent resistivities that are so low that the presence of permafrost may not be detected. The importance of establishing a site for instrument calibration, particularly for seasonal and long-term studies, is discussed.