Dilatancy-Related Electrical Resistivity Changes in Rocks

Dilatancy may lower pore pressure at mid-crustal depths to near the liquid-vapor transition of water. However, the resistivity of typical pore fluids changes very little down the transition so that changes in rock resistivity will be almost solely due to dilatant volume change. Experiments with partly saturated rocks at room temperature suggest that rocks containing mixtures of fluid and vapor, along the transition, will generally behave electrically during dilatancy as though they were fluid saturated. Observed resistivity changes before earthquakes give the dilatant volume change directly and thus may be used to further constrain the dilatancy-diffusion model, independent of observed uplift or velocity changes.