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Earthquake Light

November 20, 2023

There's a Latin adage, praemonitus praemunitus, "forewarned is forearmed." As the many deaths resulting from the recent 2023 Marrakesh–Safi earthquake and many other earthquakes illustrate, a means of earthquake prediction would be a worthy scientific goal. History is replete with reports of earthquake precursors, such as changing water levels in wells and unusual animal behavior. There's evidence that common toads may have sensed the 6.3 magnitude L'Aquila, Italy, earthquake of April 6, 2009, three days in advance.[1] Contrarily, it was found that ants did not change behavior prior to a much larger, 7.4 magnitude, earthquake.[1]

Active earthquake zones

Active earthquake zones as defined by 358,214 earthquake epicenters, 1963-1998.

(Wikimedia Commons image. Click for larger image.)

At first glance, earthquake prediction doesn't appear to be that difficult a problem. We can measure water level very accurately. The observed animal behavior might be caused by seismic tremors, and we've got great instruments to measure seismic tremors with more sensitivity than a toad. Unfortunately, these approaches have not led to effective earthquake prediction.

Scientists have investigated other potential indicators, such as the concentration of radon in well water, changes in electrical noise caused by the piezoelectric effect in rock under stress, and fractoluminescence. In fractoluminescence, the electric fields caused by separation of the crystal planes of minerals will generate light.

Considerable effort has been applied to measuring changes in local electric and magnetic fields as earthquake predictors. Observations by the Demeter (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) microsatellite, launched in mid-2004 and operational until the end of 2010, have shown a strong correlation of low frequency electromagnetic activity and seismic activity. The instruments aboard Demeter could detect electric field from DC up to 3.5 MHz, and magnetic fields from a few Hz up to 18 kHz.

Ultra-Low Frequency (ULF) electromagnetic waves were detected by Demeter as it passed over Haiti before and after the magnitude-7.0 earthquake that struck there on January 12, 2010.[2] A significant increase in ULF energy was observed in the 30 day interval before the strong earthquake, and changes in energy were also observed 25 days after, coincident with strong aftershock activity.[2]

Observation of ultra-low frequency signals appears to be a promising area for earthquake prediction. This research area began when Antony Fraser-Smith, an electrical engineer at Stanford University, detected high intensity ULF radio signals in the days leading up to the Loma Prieta earthquake in 1989.[3] His instrument was located seven kilometers from the earthquake's epicenter.[3] As sometimes happens in science, this was an accidental discovery by Fraser-Smith and a graduate student.

Fraser-Smith and his student were working on a US Navy program studying how natural noise affects satellite communication, especially the ultra-low frequency radio waves produced when the solar wind interacts with Earth's magnetosphere. Twelve days before the Loma Prieta earthquake, they recorded a large signal; and then, three hours before the earthquake, the signal went off scale. It was 20-30 times larger than the typical signal level.[3]

Preferred ULF frequencies for earthquake prediction

Preferred ultra-low frequencies for earthquake prediction. (Created using Gnumeric from data in fig. 4 of ref. 4.[4] Click for larger image.)

One potential earthquake precursor is the occurrence of earthquake lights, a skyglow sometimes coincident with an earthquake, but often reported to occur prior to seismic activity. These lights are seen near the epicenter of high magnitude earthquakes (>5 on the Richter scale), and have been seen as blue lights during earthquakes, and yellow, ball-sized lights before an earthquake. They have been noted in antiquity, also during the Peru earthquake of August 15, 2007;[5] and, most recently, during the 2023 Marrakesh–Safi earthquake.[6]

Presumed earthquake lights coincident with the 2023 Marrakesh–Safi earthquake. Clip from a YouTube video by Sabine Hossenfelder.[7]

Fractoluminescence could explain lights happening during an earthquake, but there are two processes that might explain preseismic lights. One would be electric fields created piezoelectrically by stresses in quartz-containing rocks, such as granite. Another would be triboelectricity, when dissimilar materials rub against each other. Seconds before the 2009 L'Aquila, Italy earthquake struck, 10-centimeter high flames of light were seen flickering above a street in the city's center.[8] A bright purple-pink globe of light moved through the sky along the St. Lawrence River on November 12, 1988, eleven days before a powerful earthquake.[8] In 1906, lights were seen running along the ground two nights preceding the Great San Francisco Earthquake.[8]

A 2014 study of 65 documented cases since 1600 A.D. found evidence that earthquake lights are more common at continental rifts, an example being the Gulf of California.[8] The 65 earthquakes ranged from magnitude 3.6 to 9.2, and the earthquake lights most commonly appeared as stationary or moving globular luminous masses, as atmospheric illuminations or as flame-like luminosities emerging from the ground.[8] It's theorized that stress caused charge carriers to flow along stress gradients to the surface, and then ionize air molecules to generate the earthquake lights.[8]


  1. Matt Walker, "Toads can 'predict earthquakes' and seismic activity," BBC News, March 31, 2010.
  2. M. Athanasiou, G. Anagnostopoulos, A. Iliopoulos, G. Pavlos and K. David, "Enhanced ULF radiation observed by DEMETER two months around the strong 2010 Haiti earthquake," arXiv, December 7, 2010.
  3. Anthony C. Fraser-Smith, Arman Bernardi, Robert A. Helliwell, Paul R. McGill, and O.G. Villard, Jr., "Analysis of Low-Frequency-Electromagnetic-Field Measurements Near the Epicenter," in The Loma Prieta, California, Earthquake of October 17, 1989 - Preseismic Observations, Malcolm J.S. Johnston, Editor, U.S. Geological Survey Professional Paper 1550-C (PDF file). I wrote about Robert A. Helliwell in an earlier article (Very Low Frequencies, May 27, 2019.
  4. KA Yusof, M Abdullah, NSA Hamid and S Ahadi, "On effective ULF frequency ranges for geomagnetic earthquake precursor," Journal of Physics: Conference Series, Vol. 1152, International Conference on Space Weather and Satellite Application (ICeSSAT 2018, 7-8 August 2018), DOI 10.1088/1742-6596/1152/1/012033. This is an open access paper with a PDF file here.
  5. J. A. Heraud and J. A. Lira, "Co-seismic luminescence in Lima, 150 km from the epicenter of the Pisco, Peru earthquake of 15 August 2007," Nat. Hazards Earth Syst. Sci., vol. 11, no. 4 (April 5, 2011), pp. 1025-1036, https://doi.org/10.5194/nhess-11-1025-2011.
  6. Vishwam Sankaran, "Strange ‘earthquake lights’ spotted above Morocco moments before devastating tremors remain a mystery, Independent (UK), September 12, 2023 .
  7. Possible Signs of Life on Another Planet, YouTube video by Sabine Hossenfelder, September 18, 2023.
  8. Earthquake lights linked to rift environments, subvertical faults, Seismological Society of America Press Release, January 2, 2014.
  9. Lights Flashed in the Sky During Mexico's Latest Earthquake (a magnitude 7.0 earthquake on the night of Sept. 7, 2021. Why?, YouTube video by WGBH Educational Foundation, September 27, 2021.

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