An earthquake light, also called earthquake lightning or earthquake flash, is a bright light sometimes seen in the sky near places where the Earth's crust is under pressure, during earthquakes, or around volcanic eruptions. Scientists do not agree on what causes these lights, and some people question if they really happen.

History and background

The earliest known record of earthquake lights comes from the 869 Jōgan earthquake. This event was described as "strange lights in the sky" in a historical document called the Nihon Sandai Jitsuroku, which is part of a collection of historical records called the Rikkokushi, or Six National Histories. This document was compiled for the Japanese government by Fujiwara no Tokihira. Later, in 2017, scientists Richard A. Clarke and R. P. Eddy wrote about this event in their book Warnings: Finding Cassandras to Stop Catastrophes.

A "luminous appearance" in the sky was also reported during the North Canterbury earthquake in New Zealand on September 1, 1888. Earthquake lights have been described as white or blue flashes or as glowing orbs. The distance from the earthquake’s center where these lights are seen varies. For example, during the 1930 Idu earthquake, lights were reported up to 110 kilometers (70 miles) away. In 1985, earthquake lights were seen in Mexico City after an 8.2 magnitude earthquake that occurred 740 kilometers (460 miles) away, near Pijijiapan in Chiapas, Mexico. These lights usually appear during an earthquake, though some reports describe them happening before or after, such as during the 2009 L'Aquila earthquake in Italy.

Witnesses and security cameras have sometimes captured earthquake lights during tectonic activity, such as during the 2007 Peru earthquake, the 2010 Chile earthquakes, and a 6.8 magnitude aftershock of the 2022 Michoacán earthquake.

In the past, earthquake lights were sometimes linked to religious beliefs or paranormal events like UFO sightings. Many scientists were skeptical of these reports for many years. However, scientific acceptance of earthquake lights began in the 1960s. According to National Geographic, scientists became more certain after photographs of earthquake lights taken in 1965 near Nagano, Japan, were shown to be clearly connected to geological activity. In 1973, a scientist named J. S. Derr wrote that earthquake lights are a well-known phenomenon. In 1978, T. Neil Davis from the University of Alaska Fairbanks noted that earthquake lights were no longer dismissed by scientists.

The United States Geological Survey (USGS) has been cautious about earthquake lights. In 2020, the USGS stated that some scientists believe reports of unusual lights near earthquakes might be real, while others think these reports lack strong evidence.

Types

Earthquake lights can be divided into two types based on when they happen: (1) preseismic earthquake lights, which usually appear a few seconds up to several weeks before an earthquake and are often seen closer to the earthquake's center, and (2) coseismic earthquake lights, which can occur near the earthquake's center ("earthquake-induced stress") or far away from the center during the movement of seismic waves, especially during the movement of S waves ("wave-induced stress").

According to National Geographic, earthquake lights have been reported in places like North America and Japan, as well as other areas. However, they are more frequently observed in South America, China, Germany, Greece, France, and Italy. Earthquake lights during smaller aftershocks are rare.

Proposed theories

Research on earthquake lights is still being studied. Scientists have proposed several possible reasons for these lights.

One idea is that the Earth's magnetic field or the ionosphere near areas of tectonic stress may be disturbed. This disturbance could cause glowing effects, either from light produced by ions in the atmosphere at lower altitudes or from auroras. However, these lights are not always visible during every earthquake, and scientists have not yet confirmed this explanation through direct experiments.

Seismologist Miguel Angel Santoyo explained to Nova that the lights seen in videos after the 2021 Guerrero earthquake in Mexico were caused by a mix of factors. Lightning from a regular thunderstorm at the time and electrical sparks from power lines swaying during the shaking contributed to the lights. Nova also noted that some lights in the videos were from transformers failing due to the earthquake. Other reports of earthquake lights have been linked to electrical grid disruptions, such as sparks from power lines damaged by shaking or bad weather.

Another theory suggests that intense electric fields are created when tectonic movements press against rocks containing quartz, like granite.

Some models suggest that earthquake lights may form when high stress from an earthquake breaks certain bonds in rocks like dolomite or rhyolite. This process could ionize oxygen in the rocks, creating charged particles. These ions may travel up through cracks in the rocks and into the atmosphere, where they form plasma that produces light. Laboratory tests have shown that some rocks can ionize oxygen when under high stress. Research also indicates that the angle of a fault may affect how often earthquake lights occur, with nearly vertical faults in areas of stretching rock being more likely to produce them.

At the American Physical Society's 2014 meeting, Troy Shinbrot from Rutgers University proposed that earthquake lights are caused by electrical voltage created when two layers of the same material rub together. Shinbrot tested this idea by using different types of grains to simulate Earth's crust and recreate earthquake conditions. He found that splitting grains produced positive voltage, while closing them created negative voltage. These voltage changes always produced light, a phenomenon known as triboluminescence. Scientists hope understanding this process will help improve earthquake prediction methods.

Criticism

Geologist Frederick Hutton wrote in his report to the Royal Society of New Zealand about the 1888 North Canterbury earthquake that he did not think lights seen in the sky nearby were related to earthquake activity.

In 2014, skeptic and UFO debunker Robert Sheaffer suggested that the tectonic strain theory of earthquake lights connects to research from the 1970s by Michael Persinger, a psychology professor at Laurentian University. Persinger proposed that tectonic forces might explain certain unexplained events, such as UFO sightings, poltergeist activity, animal injuries, and spontaneous human combustion, with geophysical electrical currents possibly causing the last of these. Sheaffer noted in 2014 that a paper by Robert Thériault and others on earthquake lights reused ideas that had not been proven. In 2016, Sheaffer wrote that skeptics and science bloggers should be more cautious about believing in the phenomenon. That same year, podcaster Brian Dunning expressed doubt about the existence of the phenomenon, pointing to a lack of direct evidence.