I'd never heard of these before but Ars Technica says Seismologists offer explanation for mysterious aerial light orbs preceding quakes
"'Earthquake Lights!?' exclaims one YouTube video published around about the time of the 2011 eruption of Japan's Sakurajima volcano. Or, it asks, 'UFO FLEET!?!' In the earlier part of the last century, the latter might have been a common response, but now we know that the mysterious orbs of light in white or color that appear in the sky prior to and sometimes during an earthquake, sometimes with the appearance of a rainbow spotlight or flames and sometimes lasting for hours, are actually a result of seismic activity.
Recorded sightings date back to 89BC, according to a paper on the events penned in the 90s by an Italian priest, who also jotted down associated vapors, smoke, and odors of sulphur or bitumen in the hope of providing some explanation. Today, the evidence is all over YouTube, from the 2008 Sichuan earthquake to the 2011 Christchurch quake. They're no longer disputed, but they do remain unexplained. They're rare, so it's hard to investigate them. But now a team of seismologists behind a study published in Seismological Research Letters believes it has the answer: subvertical faults in continental rifts are releasing stress-induced electrical currents up to the surface as the ground is pulled apart."