Memoirs of the Kakioka Magnetic Observatory Vol.18 No.02， p.55, November, 1979
Geomagnetic Total Force Intensity Variation associated with the Izu-Oshima Kinkai Earthquake, 1978
Ochi, K., Ijichi, N., Kuwashima, M. & Kwamura, M.
Since Nov. 1976, observations of the geomagnetic total force intensity have been carried out at Matsuzaki of the south-west coast of the Izu Peninsula.
Day to day change in night time values of the total force intensity at Matsuzaki showed an anomalous variation of about 5nT, associated with the Izu-Oshima Kinkai Earthquake 1978. This anomalous variation seems to correspond to strain change by the borehole strainmeter.
Therefore a cause of the anomalous variation may be regarded as the piezo-magnetic effect of the earth's crust, but we have not yet arrived at a full understanding of its variation.