2002 Volume 23 Issue 1 Pages 56-61
Electromagnetic grand anomalies prior to large earthquake occurrence have been paid attention especially after the 1995 Hyogo-ken Nanbu earthquake, though there is much of the debate whether the grand electromagnetic anomalies rest on sound scientific bases or not. Recent laboratory experiments conduced by Ikeya and his group using a Van de Graaff electrostatic generator suggested that such anomalies should be attributed to electrification of the ground level. In this “popular science” note, similar pre-seismic magnetic anomaly that happened at Edo age about 150 years ago is highlighted. Ansei-kenmon-shi published in 1856 noted that at the time about 2 h before destructive Ansei-Edo earth-quake in 1855, a natural magnetic stone at the Ohsumi's spectacle shop in Asakusa, Edo (Tokyo) dropped some iron nails, which had been attached to it. This observation led to the invention of a magnetic seismo-scope for prediction of earthquake occurrence. It is of interest to note that a scientist of ‘elektriciteit (electricity)’ at Edo-age, Sohkichi Hashimoto (1743−1836) had already demonstrated about 190 years ago that electrification of a natural magnetic stone was able to drop iron nails attached to it. The electromagnetic anomalies that accompanied to the Ansei-Edo earthquake were discussed in terms of the ‘Evaluation of proposed earthquake precursors’ given by American Geophysical Union.
