The shallow axial crust The RAMESSES Experiment III: Along axis variability

Implications for the fluid content of the crust

The overall resistivity of a two phase medium consisting of a liquid phase and a solid phase of much higher resistivity depends on the proportion of each present and on their distribution. A medium with a high fluid content which is distributed in isolated pockets will appear much more resistive than a medium in which the fluid content is much lower, but is distributed in a connected network throughout the solid. The Hashin-Shtrikman (HS) bounds describe an upper and lower limit on the conductivity of an isotropic two phase medium in which is the volumetric fluid fraction (Schmeling, 1986):

where is the conductivity of the solid and is the conductivity of the liquid. The upper HS bound, , describes the conductivity of a medium in which the liquid forms a completely connected network. In the case of a liquid with a conductivity much higher than that of the solid, the conductivity of the medium is dominated by conduction within the liquid phase (Waff, 1974). The lower HS bound describes the situation in which the liquid phase is included in isolated pockets, and therefore does not contribute significantly to the overall conductivity of the medium.

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