Characterization of electrical daily variations induced by capillary flow in the non-saturated zone

Electrical daily variations without an associated magnetic field were obser ved for a period of six weeks on independent parallel dipoles during the on e-year electrode inter comparison experiment that took place in Garchy, Fra nce, from April 1995 to April 1996. These daily variations appeared suddenl y during summer when the soil was dry on the surface. Their amplitude range d from 0.1 to 1.5 mV for 50-m long dipoles. and characteristic relative pha ses. The amplitude of the variations was found to be related to soil temper ature. These daily variations are accounted for in a model where streaming potentials are produced by coherent capillary Row in the non-saturated zone . Such daily variations are important to control in long-period magnetotell uric sounding and may be of practical use for agricultural applications. As their amplitude strongly depends on time-varying soil conditions, they may also lead to erroneous interpretations as earthquake precursors.