Low frequency seismogenic electromagnetic emissions as precursors to earthquakes and volcanic eruptions in Japan


A multipoint network was constructed in the Tokyo area for earthquake prediction using seismogenic electromagnetic emissions. The network consists of eight observation points within 50 km of each other.Each point has a digital direction-finding detector with two loop sensors tuned to 82 kHz. The output signals of the receivers are added into a digital vector composition circuit to obtain the direction angle of the source point,and this signal is telemetered to the central computer.To protect from false alarms caused by local man-made noise interference,the warning is announced only when there is a high cross-correlation between almost all detectors pointing to one small area. The mechanism of these earthquake precursors can be explained as electromagnetic emissions from the rocks around the focus when they are crushed completely by the distortion pressure. These emissions propagate along the fault plane as an EM surface wave mode and radiate from the slit antenna formed by the intersection of the fault plane and ground surface.In the last five years, we have detected impulsive noise bursts of seismogenic emissions at 82 kHz, 1.525 kHz, and 36 Hz using our multipoint detection network around the Tokyo region and Izu peninsula. This system has recorded EM signals prior to the following events: volcanic eruptions on November 15 and 2 1, 1986 at Mt. Mihara on Ohshima Island, and on July 12, 1989 in Itoh Bay in the Izu peninsula region, and also a minor earthquake on October 14, 1989 at Ohshima Island

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