Self‐potential variations with time and their relation to hydrogeologic and meteorological parameters

Abstract

A systematic investigation of self potentials (SP) shows that they vary considerably with time. To study the influencing parameters, repeated measurements were conducted every 14 days over a period of a year and a half along fixed profiles which extended over different lithological units. An analysis of the recorded SP suggests decomposition into three components of different wavelengths. Variations of the SP with wavelengths in the 0.1–1 m range and amplitudes of up to 150 mV are thought to be induced by vegetation. The mean amplitudes change with a one‐year period, and there is a rough correlation with the soil temperature. A long‐wavelength component (wavelengths, meters and some tens of meters; amplitudes, some 10 mV) is attributed to changes of the underground lithology. The long‐wavelength SP and its pronounced variation with time are assumed to be caused by water movements in layers of different permeability. A morphology‐dependent trend of the SP values which has been much disputed in the literature shows systematic variations with time, too, with gradients changing on the order of .5 mV/m difference in elevation. There is a correlation with precipitation with a one‐month time lag. This effect is assumed to result from depletion and recharge of perched water aquifers. Measurements at the surface and at shallow depth establish the existence of a vertical gradient of the SP which shows variations with time of up to 50 mV/m. With a three‐month time lag, the amplitude of the vertical gradient relates closely to the variation of the potential evapotranspiration. Groundwater recharge from gravitational water is considered the main cause of the vertical gradient. The results suggest that self potentials at the nearsurface must be regarded primarily as being of a streaming‐potential character. Their variation with time should not be neglected when the SP method is applied to problems in engineering geophysics. On the other hand, the results confirm that because of the close relation between self potentials and hydrogeologic parameters, SP measurements may become a valuable and standard technique in hydrogeology.

The summit hydrothermal system of Stromboli. New insights from self-potential, temperature, CO 2 and fumarolic fluid measurements, with structural and monitoring implications

“…In the absence of a hydrothermal system, fluid flow will be restricted to the mostly vertical flow of vadose water towards a water table. The linear reverse relationship between SP and altitude commonly observed on the flanks of volcanoes is thought to be related to an increase in thickness of the vadose zone with altitude (Zablocki 1978;Schiavone and Quarto 1984;Ernstson and Scherer 1986;Jackson and Kauahikaua 1987;Aubert and Atangana 1996;Aubert et al 1990Aubert et al , 1991Aubert et al , 1993. At Kilauea volcano, Jackson and Kauahikaua (1987) showed that this relationship can be used to detect water table depth.…”

A One-Year Systematic Study of Electrodes for Long Period Measurements of the Electric Field in Geophysical Environments

“…As the salt was removed, the potential sampled by the electrode through the volume average of the conductive salted zone was changing accordingly. The natural soil has indeed an heterogeneous electrical structure, and SP varies on a few cm distance by a few mV (Ernstson and Scherer, 1986;Clerc et al, 1997).…”

“…The fabrication is still a largely undocumented craft and there seems to be no consensus on the performances of the various types of electrodes (Junge, 1990;Larsen, 1992;Erkul and Muller, 1996). Although some systematic studies of the time variations of SP have been undertaken (Ernstson and Scherer, 1986), many phenomena related to the electrochemical contact with the external medium are still unknown.…”

Self-potential investigation of moraine dam seepage

“…This anomaly is interpreted as resulting from shallow, gravitational groundwater flow in the nearsubsurface from the crest to the toe, similar to the "negative summit" phenomenon commonly observed in SP surveys over steep terrain (e.g. Corwin, 1989;Corwin and Hoover, 1979;Ernstson and Scherer, 1986). Interestingly, however, the most negative SP does not occur at the crest of the dam (though measurements are admittedly sparse in this area), an observation that is explored in Section 5.1 of the Discussion.…”