An earthquake light is an unusual luminous aerial phenomenon that reportedly appears in the sky at or near areas of tectonic stress, seismic activity, or volcanic eruptions. Once commonly challenged, it was not until photographs were taken during the Matsushiro earthquake swarm in Nagano, Japan (which occurred from 1965 through 1967) that the seismology community acknowledged their occurrence.
The lights are reported to appear while an earthquake is occurring, although there are reports of lights before or after earthquakes, such as reports concerning the 1975 Kalapana earthquake. They are reported to have shapes similar to those of the auroras, with a white to bluish hue, but occasionally they have been reported having a wider color spectrum. The luminosity is reported to be visible for several seconds, but has also been reported to last for tens of minutes. Accounts of viewable distance from the epicenter varies: in the 1930 Idu earthquake, lights were reported up to 70 miles (110 km) from the epicenter. Earthquake lights were reportedly spotted in Tianshui, Gansu, approximately 400 kilometres (250 mi) north-northeast of the earthquake's epicenter. During the 2007 Peru earthquake lights were seen in the skies above the sea and filmed by many people. The phenomenon was also observed and caught on film during the 2009 L'Aquila  and the 2010 Chile earthquakes. Video footage has also recorded this happening during the 9 April 2011 eruption of Sakurajima Volcano, Japan. The phenomenon was also reported around the Aimuri Earthquake in New Zealand, that occurred 1 September 1888. The lights were visible in the morning of 1 September in Reefton, and again on 8 September.
Earthquake lights are caused by an unknown mechanism. There are numerous theories as to how and why they occur.
Another possible explanation is local disruption of the Earth's magnetic field and/or ionosphere in the region of tectonic stress, resulting in the observed glow effects either from ionospheric radiative recombination at lower altitudes and greater atmospheric pressure or as aurora. However, the effect is clearly not pronounced or notably observed at all earthquake events and is yet to be directly experimentally verified.
 See also
- "November 29, 1975 Kalapana Earthquake". Hvo.wr.usgs.gov. Retrieved 2010-09-13.
- Lane, F. W. The Elements Rage (David & Charles 1966), pp. 175–6
- Paul Simons (2008-03-15). "Glowing lights around an earthquake's epicenter". London: Times Online. Retrieved 2008-05-20.
- "The earthquake lights (EQL) of the 6 April 2009 Aquila earthquake, in Central Italy, NHESS, V.10". 2010. p. 967.
- "Registran enormes luces en el cielo durante terremoto de 88 grados de magnitud que destruyo Chile". Lima: Peru Online. 2010-02-28. Retrieved 2010-03-01.
- "Transactions and Proceedings of the Royal Society of New Zealand 1868-1961".
- Takaki, Shunji and Ikeya, Motoji, A Dark Discharge Model of Earthquake Lightning, Japanese Journal of Applied Physics, Volume 37, Issue 9A, p. 5016 (1998).
- "'Restless Earth' May Give Advance Notice of Large Earthquakes : News". Earthobservatory.nasa.gov. 2001-12-07. Retrieved 2010-09-13.