What happened
In August 1965, one of the best-documented earthquake swarms in history began beneath Matsushiro, on the outskirts of Nagano. By 1967 about a million tremors had been recorded, and at the worst of it residents felt them every few minutes. During this period a glow was repeatedly seen over the area – white, bluish, red, or orange – which flared up suddenly, lasted several tens of seconds, and was sometimes so bright that it was mistaken for a fire or the dawn. A local dentist took a series of photographs of these lights, which are regarded as the first photographs of the phenomenon. The accounts were collected and described by the Japan Meteorological Agency, and the material from Matsushiro convinced many seismologists that earthquake lights are not merely a legend.
Witnesses
Residents of the Matsushiro area; a series of photographs was taken by a local dentist, and the accounts were collected by the Japan Meteorological Agency.
Explanations and hypotheses
The existence of earthquake lights is now widely accepted, but their mechanism remains a matter of debate. Proposed explanations include piezoelectric effects, electrification of fracturing rocks, and charges released from rocks under stress that ionize the air. Some seismologists, including Tsuneji Rikitake, expressed doubts about the authenticity of some of the Matsushiro photographs, and other reports of earthquake lights are explained by arcing power lines.
Disputed A likely explanation exists, but some of the facts are still disputed.
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