Spooky lights heralding the onset of earthquakes have been tied to divine portents or UFO sightings in the past. But the true culprit may be certain rocks that release electric charges when stressed by the Earth's seismic shifts, researchers say.
The strange phenomena of earthquake lights—sometimes resembling bluish flames, lightning strikes, or floating orbs—can be explained by tiny crystal defects in certain rocks that can release electric charges, according to National Geographic. Researchers examined the historical record of earthquake lights from around the world and detailed their latest findings in the journal Seismological Research Letters.
Recent theories have focused on the disruption of the Earth's magnetic field or the piezoelectric effect of producing electricity by squeezing certain crystals such as quartz. But the new research points to a different electronic process related to certain rocks such as basalts and gabbros. Such rocks can be found in "dike" structures that formed as magma cooled in vertical faults reaching as deep as 97 kilometers underground.
The stressed rocks release charge when triggered by seismic waves accompanying earthquakes, says Friedemann Freund, a senior researcher at NASA's Ames Research Center and co-author on the paper. The charges travel along the dikes toward the surface, combining with one another to form a "plasma-like state," and finally emerge to create electrical discharges in the air related to the earthquake light displays.
Such lights only occur for less than 0.5 percent of earthquakes worldwide, according to the paper's estimates. They appear most common in Italy, Greece, France, Germany, China, and South America. But they have excited observers in regions as far apart as Japan and North America. (The image for this story comes from Jim Conacher, a retired Canadian government agriculture inspector, who took a photo of yellow orbs floating on a mountain near Tagish Lake in Canada—just a few hours before the nearby Cross Sound earthquake occurred on 1 July 1973.)
Freund has written about the electromagnetic phenomena related to earthquakes for IEEE Spectrum in the past. He previously examined radio frequency phenomena connected to some earthquakes and showed how the Earth's crust can act like a huge battery driving a geological radio circuit extending more than 30 kilometers underground.
The NASA researcher is currently working with other scientists to integrate earthquake lights sightings with a global earthquake forecasting system. Such spooky sightings could prove a useful indicator of a possible impending earthquake when detected alongside other earthquake indicators.
But not everyone envisions such forecasting benefits from earthquake lights. Bruce Presgrave, a geophysicist with the U.S. Geological Survey's National Earthquake Information Center, told National Geographic that the infrequent occurrence of earthquake lights would likely limit their use in forecasts.
Photo: Jim Conacher