Fast-decaying inductive IP in frozen ground

摘要

Effects of induced polarization (IP) often appear in TEM data collected in Yakutia and elsewhere in permafrost areas. Inversion of transient responses using the Cole-Cole model of frequency-dependent conductivity shows fast decaying induced polarization in the shallow subsurface (within 100 m). Frozen ground within these depths has the chargeability (. m) in the range from 0.2 to 0.85 (mostly 0.2-0.5); the relaxation time constant (τ) varies from 35 to 250 μs being 50-100 μs on average, and the exponent. c is little variable, unlike. m and τ (from 0.8 to 1).The latter fact (. c ≈ 1) is indicative of a narrow range of relaxation times fitting the Debye relaxation model. Conversion of the complex conductivity into relative low-frequency dielectric permittivity results in values of the order of tens of thousands or a few hundred thousand. These exceptionally high permittivities have no other plausible explanations than electrochemical polarization of unfrozen water that remains bound on the surface of mineral grains at subzero temperatures. The effects of electrochemical polarization are described and interpreted in terms of frequency-dependent surface conductivity, which is controlled by surface-to-volume ratio.