HR: 14:00h
AN: H23H-02 INVITED    [Abstracts]
TI: Limitations and Perspectives of Electrical Resistivity and Refraction Seismic Tomography in Frozen Ground
AU: * Hauck, C
EM: hauck@imk.fzk.de
AF: Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe, Postfach 3640, Karlsruhe, 76021, Germany
AU: Rings, J
EM: rings@imk.fzk.de
AF: Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe, Postfach 3640, Karlsruhe, 76021, Germany
AB: Determining the subsurface ice and unfrozen water content in cold regions are important tasks in all kind of cryospheric studies, but especially on perennial or seasonal frozen ground, where little insights can be gained from direct observations at the surface. In the absence of boreholes, geophysical methods are often the only possibility for visualising the subsurface characteristics, and their successful application in recent years included 2D/3D monitoring and even quantifying the ice and unfrozen water content evolution within the subsurface. Due to the strong sensitivity of electrical resistivity, permittivity and seismic velocity to the phase change from unfrozen water to ice, the application of electrical, electromagnetic and seismic techniques has been especially successful. Within these methods, Electrical Resistivity Tomography (ERT) is often favoured due to its comparatively easy and fast data processing, its robustness against ambient noise and its good performance even in cold and irregular environments. Numerous studies have now shown that ERT is principally suitable to map ground ice, differentiate between ice-poor and ice-rich occurrences, monitor freezing, thawing and infiltration processes, and determine the origin of the ice, i.e. a differentiation between buried glacier ice and segregation ice. However, in practice, a number of uncertainties often prohibit a reliable determination of the material composition from ERT surveys alone. Sources of uncertainty are based on the necessity to choose a set of inversion parameters for calculating the specific resistivity distribution from the measured apparent resistivity data set. In addition, high contact resistances at the surface, large topographic gradients, measurement geometry and the presence of fine material or saline pore water can influence the obtained specific resistivity values. Consequently, it is generally advisable to apply a combination of different geophysical methods at each field site. In this contribution we will analyse the reliability of ERT and refraction seismic results regarding the above uncertainties by using multiple inversions and forward modelling techniques for data sets from different permafrost occurrences in the European Alps and Antarctica. Addressing the inherent uncertainty of ERT an inversion ensemble approach is introduced using multiple inversions of the same data set and clustering techniques to obtain the dominant, and therefore most reliable, subsurface features. In addition, combined electrical resistivity and seismic surveys are presented for a detailed quantification of the material composition in frozen ground.
DE: 0702 Permafrost (0475)
DE: 0770 Properties
DE: 0794 Instruments and techniques
DE: 1823 Frozen ground
DE: 1835 Hydrogeophysics
SC: Hydrology [H]
MN: 2007 Fall Meeting