HR: 13:30h
AN: NS43A-01 INVITED     [Abstracts]
TI: Geophysical Techniques for Detecting, Analysing and Monitoring Frozen Ground
AU: * Hauck, C
EM: hauck@imk.fzk.de
AF: Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe/University of Karlsruhe, Postfach 3640, Karlsruhe, 76021 Germany
AB: Permafrost degradation due to contemporary climatic change has a significant impact on the stability of mountain slopes, buildings and infrastructure in permafrost regions. In order to assess the potential risks of accelerated permafrost thawing and develop suitable mitigation strategies, ground ice occurrences have to be detected, mapped and monitored on various temporal and spatial scales. Applications of geophysical techniques for permafrost detection present comparatively cheap and logistically feasible alternatives to the single point information from boreholes. Recently applied methods include electrical resistivity tomography (ERT), refraction seismic tomography, electromagnetic induction methods and ground penetrating radar (GPR). In this contribution the different geophysical methods are evaluated concerning their applicability on frozen ground based on numerous field and laboratory studies. The advantages and disadvantages of each method concerning sensor coupling in heterogeneous and blocky terrain, steep topography, measurement accuracy and interpretational ambiguities are discussed. In addition, the indirect nature of geophysical soundings requires a relation between the measured variable (e.g. electrical resistivity, seismic velocity) and the respective parts of the material composition (rock, water, air, ice) - in our case the ice content. With combined resistivity and seismic data sets as input variables the ice and unfrozen water contents of the subsurface can be calculated using a 4-phase model. The model is based on two well-known geophysical mixing rules for electrical resistivity and seismic P-wave velocity, Archie's law and Timur's equation. In addition to prescribing the material dependent free parameters in Archie's law, the resistivity and P-wave velocity of the rock material and the pore water have to be known in advance. Besides, one of the volume fractions has to be explicitly prescribed (usually the porosity). First results confirm the good model performance for various field cases in permafrost research. Extensive validation using a series of shallow boreholes is needed to further analyse the quantitative performance of the model for different glacial and periglacial environments.
DE: 1823 Frozen ground
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 5109 Magnetic and electrical properties
DE: 5194 Instruments and techniques
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly