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International Journal of Geophysics
Volume 2012, Article ID 270809, 10 pages
http://dx.doi.org/10.1155/2012/270809
Research Article

Electric Signals on and under the Ground Surface Induced by Seismic Waves

1Earthquake Prediction Research Center, Institute of Oceanic Research and Development, Tokai University, 3-20-1 Orido, Shimizu-ku, Shizuoka 424-8610, Japan
2Division of Information and Communications Systems Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino 191-0065, Japan
3Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan

Received 31 May 2011; Revised 2 November 2011; Accepted 18 November 2011

Academic Editor: Laurence Jouniaux

Copyright © 2012 Akihiro Takeuchi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We constructed three observation sites in northeastern Japan (Honjo, Kyowa, and Sennan) with condenser-type large plate electrodes (4 × 4 m2) as sensors supported 4 m above the ground and with pairs of reference electrodes buried vertically at 0.5 m and 2.5 m depth (with a ground velocity sensor at Sennan only). Electrical signals of an earthquake (M6.3) in northeastern Japan were detected simultaneously with seismic waves. Their waveforms were damped oscillations, with greatly differing signal amplitudes among sites. Good positive correlation was found between the amplitudes of signals detected by all electrodes. We propose a signal generation model: seismic acceleration vertically shook pore water in the topsoil, generating the vertical streaming potential between the upper unsaturated water zone and the lower saturated water zone. Maximum electric earth potential difference was observed when one electrode was in the saturated water zone, and the other was within the unsaturated water zone, but not when the electrodes were in the saturated water zone. The streaming potential formed a charge on the ground surface, generating a vertical atmospheric electric field. The large plate electrode detected electric signals related to electric potential differences between the electrode and the ground surface.