Seismoelectric Studies In An Outwash Plain

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