An earthquake light also known as earthquake lightning or earthquake flash is a luminous optical phenomenon that appears in the sky at or near areas of tectonic stress, seismic activity, or volcanic eruptions. There is no broad consensus as to the causes of the phenomenon (or phenomena) involved. The phenomenon differs from disruptions to electrical grids – such as arcing power lines – which can produce bright flashes as a result of ground shaking or hazardous weather conditions.
Appearance
One of the first records of earthquake lights is from the 869 Sanriku earthquake, described as "strange lights in the sky" in Nihon Sandai Jitsuroku. 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 from the epicenter. Earthquake lights were reportedly spotted in Tianshui, Gansu, approximately north-northeast of the 2008 Sichuan earthquake's epicenter.
During the 2003 Colima earthquake in Mexico, colorful lights were seen in the skies for the duration of the earthquake. 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. The phenomenon was also reported around the North Canterbury 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.
More recent appearances of the phenomenon, along with video footage of the incidents, happened in Sonoma County, California on August 24, 2014, and in Wellington, New Zealand on November 14, 2016, where blue flashes like lightning were seen in the night sky, and recorded on several videos. On September 8, 2017, many people reported such sightings in Mexico City after a 8.2 magnitude earthquake with epicenter away, near Pijijiapan in the state of Chiapas.
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.
Instances of this phenomenon appear in videos taken seconds after a 7.1 magnitude earthquake in the city of Acapulco, Mexico, around 20:47 on 7 September 2021. The New York Times reported that "Videos from both Acapulco and Mexico City also showed the night sky lit up with electrical flashes as power lines swayed and buckled."
A recent one was seen in Qinghai Province, China at 01:45 on 8 January 2022. Surveillance video of a local resident captured the moment. During the 2022 Fukushima earthquake the phenomena was captured on video from multiple angles.
This phenomenon was observed around 1:18 on 22 September 2022 when a magnitude 6.8 aftershock of the 2022 Michoacán earthquake struck. Social media users including Webcams de México posted videos of blue lights which seemed to be radiating upward. This was reported in Mexico News Daily and included one of the videos.
During the 2023 Turkey–Syria earthquake, multiple lights appeared continuously in Kahramanmaraş and Hatay provinces. Later that year, blue light flashes were also seen in Agadir during the Marrakesh-Safi earthquake.
Types
Earthquake lights may be classified into two different groups based on their time of appearance: (1) preseismic earthquake light, which generally occur a few seconds to up to a few weeks prior to an earthquake, and are generally observed closer to the epicenter and (2) coseismic earthquake light, which can occur either near the epicenter ("earthquake‐induced stress"), or at significant distances away from the epicenter during the passage of the seismic wavetrain, in particular during the passage of S waves ("wave‐induced stress").
Earthquake light during the lower magnitude aftershock series seem to be rare.
Possible explanations
Research into earthquake lights is ongoing; as such, several mechanisms have been proposed.