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 2008 Sichuan 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 Amuri 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. A more recent appearance of the phenomenon, along with video footage of the incident, happened in Sonoma County of California on August 24, 2014.
Appearances of the earthquake light seem to occur when the quakes have a high magnitude, generally 5 or higher on the Richter scale. There have also been incidents of yellow, ball-shaped lights appearing before earthquakes.
Hypotheses and models
Research into earthquake lights is ongoing; as such, several mechanisms have been proposed.
The most recent model suggests that the generation of earthquake lights involves the ionization of oxygen to oxygen anions by breaking of peroxy bonds in some types of rocks by the high stress before and during an earthquake. After the ionisation, the ions travel up through the cracks in the rocks. Once they reach the atmosphere these ions can ionise pockets of air, forming plasma that emits light. Lab experiments have validated that some rocks do ionise the oxygen in them when subjected to high stress levels. Research suggests that the angle of the fault is related to the likelihood of earthquake light generation, with subvertical (nearly vertical) faults in rifting environments having the most incidences of earthquake lights.
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.
During the American Physical Society's 2014 March meeting, research was provided that gave a possible explanation for the reason why bright lights sometimes appear during an earthquake. The research stated that when two layers of the same material rub against each other, voltage is generated. The researcher, Professor Troy Shinbrot of Rutgers University, conducted lab experiments with different types of grains to mimic the crust of the earth and emulated the occurrence of earthquakes. "When the grains split open, they measured a positive voltage spike, and when the split closed, a negative spike." The crack allows the voltage to discharge into the air which then electrifies the air and creates a bright electrical light when it does so. According to the research provided, they have produced these voltage spikes every single time with every material tested. While the reason for such an occurrence was not provided, Professor Troy Shinbrot referenced the light to a phenomenon called triboluminescence. Researchers hope that by getting to the bottom of this phenomenon, it will provide more information that will allow seismologist to better predict earthquakes.
- "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.
- Fidani, C. (2010). "The earthquake lights (EQL) of the 6 April 2009 Aquila earthquake, in Central Italy". Natural Hazards and Earth System Science 10 (5): 967–78. doi:10.5194/nhess-10-967-2010.
- Fidani, C. (March 2012). "Statistical and spectral properties of the L'Aquila EQL in 2009". Bollettino di Geofisica Teorica ed Applicata 53 (1): 135–46. doi:10.4430/bgta003 (inactive 2015-01-09).
- "Registran enormes luces en el cielo durante terremoto de 88 grados de magnitud que destruyo Chile" [Recorded huge lights in the sky during the earthquake of 8.8 magnitude that destroyed Chile] (in Spanish). Peru Online. February 28, 2010.
- Hutton (1888). "The Earthquake in the Aimuri". Transactions and Proceedings of the Royal Society of New Zealand 1868-1961 21: 269–353.
- Carter, Lori (25 August 2014). "Did you see flashes? Yep, an earthquake can create ’em (w/video)". Press Democrat (Press Democrat). Retrieved 9 September 2014.
- Howard, Brian Clark. "Bizarre Earthquake Lights Finally Explained". National Geographic. Retrieved 25 August 2014.
- Thériault, Robert; St-Laurent, France; Freund, Friedemann T.; Derr, John S. (2014). "Prevalence of Earthquake Lights Associated with Rift Environments". Seismological Research Letters (Seismological Society of America) 85 (1): 159–178. doi:10.1785/0220130059. ISSN 0895-0695. Lay summary – Seismological Society of America (January 2, 2014).
- Takaki, Shunji; Ikeya, Motoji (1998). "A Dark Discharge Model of Earthquake Lightning". Japanese Journal of Applied Physics 37: 5016–20. Bibcode:1998JaJAP..37.5016T. doi:10.1143/JJAP.37.5016.
- "'Restless Earth' May Give Advance Notice of Large Earthquakes" (Press release). NASA. December 7, 2001. Retrieved January 4, 2014.
- Choi, Charles. "Mysterious Flashing 'Earthquake Lights' Maybe Explained". livescience. Retrieved 9 September 2014.
- Kim, Meeri. "Experiments at Rutgers lend credence to existence of ‘earthquake lights’". Washington Post. Retrieved 9 September 2014.
- Luntz, Stephen. "Clue To Mysterious Lights That Appear Before Earthquakes". Iflscience!. Retrieved 9 September 2014.