Instead, about 85 percent of the time, lights seemed to happen at places where the tops of the continental plates buckle, creating fissures, or rifts, where the Earth pulls apart.
"You have two sides of a piece of continent (that) are pulling apart and in the middle there's a part that just falls vertically down," often by miles over millions of years, Freund told LiveScience.
These rifts form steep, nearly vertical faults that stretch deep into the Earth's magma, allowing primitive magmatic rocks that were once deep below ground to migrate closer to the Earth's surface.
The authors think that because of the crystal structure of these magmatic rocks, when stressed they are likelier to generate electricity, which then flows to the Earth's surface, ionizes the air, and produces flashes of light.
The earthquake lights also appeared at other nearly vertical faults, for example, the strike-slip San Andreas fault. These faults likely make it easier for electrical charges in these dark magmatic rocks to reach the surface, said study co-author John Derr, a seismologist at the Albuquerque Seismological Laboratory.
Still, the distance from the epicenter of the quake, and the timing of the light show, can be very different. Sometimes, earthquake lights aren't even associated with earthquakes, Freund said.
That's because electrical current can flow from a stress buildup that could either be released in a catastrophic rupture, or gradually over several days, with no quakes.
Two of the earthquake lights noted in the records appeared near subduction zones, but they may actually have been caused by hidden, nearly vertical faults within the subduction zone that are buried under water or layers of sediment, Freund said.
With many subduction zones out in the deep ocean, it's likely that more earthquake lights are reported near intraplate faults, since that's where people live. But even if the flashing lights did form out in the ocean, the water would dampen the electricity and prevent the lights from emerging, Freund said.
It’s not clear exactly why subduction zones don't seem to be good locations for these earthquake lights, but one possibility is that nearly vertical faults are better at transferring stresses formed deep below the Earth to the surface, said Patrick Hogan, a project manager at NASA's World Wind project in Mountain View, Calif., who was not involved in the study.
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This story originally appeared on LiveScience.com.