Electrical and seismic response of saline permafrost soil during freeze - Thaw transition

Yuxin Wu, Seiji Nakagawa, Timothy J. Kneafsey, Baptiste Dafflon, Susan Hubbard

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59 Scopus citations

Abstract

We conducted laboratory studies on the geophysical signals from Arctic saline permafrost soils to help understand the physical and mechanical processes during freeze-thaw cycles. Our results revealed low electrical resistivity (< 20 Ωm) and elastic moduli (7.7 GPa for Young's modulus and 2.9 GPa for shear modulus) at temperatures down to ~− 10 °C, indicating the presence of a significant amount of unfrozen saline water under the current field conditions. The spectral induced polarization signal showed a systematic shift during the freezing process, affected by concurrent changes of temperature, salinity, and ice formation. An anomalous induced polarization response was first observed during the transient period of supercooling and the onset of ice nucleation. Seismic measurements showed a characteristic maximal attenuation at the temperatures immediately below the freezing point, followed by a decrease with decreasing temperature. The calculated elastic moduli showed a non-hysteric response during the freeze – thaw cycle, which was different from the concurrently measured electrical resistivity response where a differential resistivity signal is observed depending on whether the soil is experiencing freezing or thawing. The differential electrical resistivity signal presents challenges for unfrozen water content estimation based on Archie's law. Using an improved formulation of Archie's law with a variable cementation exponent, the unfrozen water content estimation showed a large variation depending on the choice of the resistivity data during either a freezing or thawing cycle. Combining the electrical and seismic results, we suggest that, rather than a large hysteresis in the actual unfrozen water content, the shift of the resistivity response may reflect the changes of the distribution pattern of the unfrozen water (or ice) in the soil matrix during repeated freeze and thaw processes. Collectively, our results provide an improved petrophysical understanding of the physical and mechanical properties of saline permafrost during freeze – thaw transitions, and suggest that large uncertainty may exist when estimating the unfrozen water content using electrical resistivity data.

Original languageEnglish
Pages (from-to)16-26
Number of pages11
JournalJournal of Applied Geophysics
Volume146
DOIs
StatePublished - Nov 2017
Externally publishedYes

Funding

The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. We acknowledge Craig Ulrich (LBNL), John Peterson (LBNL), Alexander Kholodov (UAF), Cathy Wilson (LANL) and David Graham (ORNL) for their help with field coring efforts. This NGEE-Arctic research is supported through contract number DE-AC0205CH11231 to Lawrence Berkeley National Laboratory. We gratefully acknowledge the project PI, Stan Wullschleger at ORNL. The datasets presented in this research are available at http://dx.doi.org/10.5440/1374172 .

Keywords

  • Electrical resistivity
  • Freeze – thaw
  • Induced polarization
  • Saline permafrost
  • Seismic property
  • Unfrozen water content

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