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Self-potential

The ugly duckling of environmental geophysics

Temple University, Philadelphia, Pennsylvania, U.S.

Charles E. Corry

Colorado Springs, Colorado, U.S.

Corresponding author: nyq@nimbus.temple.edu

The first 20% of the full text of this article appears below.

Self-potential (SP) is the method that everyone knows about but nobody seems to appreciate. Out of more than 850 papers published in the Symposium for the Application of Geophysics to Environmental and Engineering Problems (SAGEEP) between 1988 and 2001, 63 included SP as a key word, but most mentioned it only in passing.

This is surprising when you consider that SP is nonintrusive, fast, and inexpensive, requiring little more than a voltmeter and a few nonpolarizing electrodes, and that environmental geophysical surveys are typically low-budget operations. What is doubly surprising is that less than a handful of the 850 SAGEEP papers discussed SP anomalies of electrochemical origin, even though electrochemical potentials associated with ore bodies are by far the most important source of SP in the mining industry.

The majority of environmental papers that focused on SP as the primary geophysical method discussed the mapping of seepage in dams, embankments, leaky containment ponds, and other sources of streaming potential. Two possible reasons for this apparent lack of enthusiasm for SP among environmental geophysicists are electrical noise and difficulties with interpretation.

Exploration geophysicists are familiar with SP noise sources such as telluric currents, electrode drift, topographic effects associated with streaming potentials, photovoltaic potentials, and changes in soil composition, moisture, and vegetative cover. But environmental sites add power lines, buried utilities (some cathodically protected), grounded fences and equipment, corroding scrap metal, and other man-made sources to the list of undesired voltages. For instance, we have observed an electric rail system create an SP interference 1 km away; an interference from electric ore trains more than 20 km from the survey area; and a data logger's large increase in the SP noise levels between about 8 A.M. and 4:30 P.M., coinciding with the day shift at . . . [Full Text of this Article]