Observation of atmospheric electricity variation signals during underground seismic wave propagation

We have installed an underground electromagnetic observation room in the Hosokura mine in Miyagi Prefecture (Hosokura observation room) to observe the variation in atmospheric electromagnetic signals. In this room, we have set up a large plate electrode to observe signal variation of atmospheric electricity. With this, we have observed co-seismic electromagnetic phenomena. During the two medium earthquakes that occurred on 27 and 29 February 2004, we observed clear co-seismic signals in the plate electrode potential variation in the room. A model of the appearance of these signals is examined to explain the observed data. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.