Seismoelectric Studies in an Outwash Plain

Abstract

Initial studies of the seismoelectric effect in an outwash plain have been conducted near Yellow Springs, Ohio. The purpose was to make seismoelectric measurements in a simple, well-understood test site where the seismoelectric signals could be clearly recorded and theoretical predictions could be calculated with as few assumptions as possible. Suppression of electrical noise was a major concern because 60 Hz electromagnetic fields from the power grid system are unavoidable in most parts of the United States. The site was characterized by seismic refraction surveys, DC resistivity surveys, and two drill holes. The site has a fairly uniform, 3 m thick unsaturated layer over a thick saturated sandy layer. The water table was near the top of the outwash layer. For the seismoelectric studies a sledgehammer source was used. Seismic signals and electrical signals were recorded separately and jointly with a variety of electrode combinations. An engineering seismograph was used to record both the seismic and electrical signals. The built-in 60 Hz and 180 Hz notch filters were effective in suppressing much of the power grid pickup. Electrical signals were observed which were consistent in time and frequency with the expectation of seismoelectric response due to the electrokinetic effect. Themore » peak-to-peak electric field amplitude was about 6 mV/m and the time delay corresponded with one-way seismic travel times to the water table.« less