For hundreds of years lightning-like flashes have been reported before earthquakes. The stores have been common enough to gain some credibility, but with no known mechanism and witnesses often distressed after the quake, scientists were sceptical until videos started to appear. Now, however, electrical charges that could be responsible have been produced in the laboratory, although the mechanism still remains poorly understood.

Earthquake lights are usually bluish-white and last for a few seconds. They've been reported up to 400km from the epicenter of earthquakes and last for several seconds – although there are claims of much longer lasting events. Multiple explanations have been proposed, including the ionization of oxygen within certain rocks and disruption of the Earth's magnetic field. Whatever is driving the lights could also explain the reports of animals behaving strangely prior to earthquakes, and even individuals who get particular headaches.

Naturally, many mystical interpretations have also been proposed but, in the words of Tim Minchin, “Throughout history, every mystery ever solved has turned out to be...not magic.”

A third hypothesis proposed by scientists is that the lights are a result of piezoelectricity produced when certain materials experience mechanical stress. While this seems the closest to what has now been observed in the lab, the experimental results suggest electric fields can be produced with a much wider range of substances than previously thought possible.

Presenting at the American Physical Society March Meeting, Professor Troy Shinbrot of Rutgers University said, "We took a tupperware container filled with flour, tipped it back and forth until cracks appeared, and it produced 200 volts of charge.” Given the resistant nature of the materials used the actual current produced are tiny, even when the voltage is high.

Shinbrot and his colleagues were trying to solve the problem of pharmaceutical powders sticking to surfaces when charged. However, when he read about earthquake lights it struck him that he had the equipment to test what might be occurring.

The behavior is not limited to flour. Shinbrot and his team repeated the observations with glass particles and small plastic disks, although voltages varied. Over kilometers of fault-line the charge could build up to millions of volts, leading to discharges similar to lightning.

“Our first suspicion was that this has to be a mistake,” Shinbrot said. “We did many tests to try to rule out these spurious effects, and so far we have failed.”

Nevertheless, the discovery raises as many questions as it answers. "There isn't a mechanism I know that can explain this. It seems to be new physics," said Shinbrot. While comparisons with static electricity are inevitable, Shinbrot points out these involve the rubbing of materials with different affinity to charge. His finding however, involves, “two layers of exactly the same material rubbing against each other - and generating voltage.” He admits to having no idea how this is happening, although it may be related to triboluminesence, the phenomenon of energy released when solids are crushed or rubbed, for example sticky tape emitting X-rays when unpeeled in a vacuum.

It is also not clear why earthquake lights sometimes appear days before or after the main quake.

Using the phenomenon to provide warning for quakes will not be easy. "Not every major earthquake is preceded by lightning. And not all clear-sky lightning is followed by earthquakes,” says Shinbrot. "We want to know - why does this lightning appear sometimes but not others?"

Independently of this discovery, towers have been placed in earthquake-prone regions of Turkey to try to get a handle of what is going on. "They've found there do seem to be precursors for some large earthquakes - magnitude 5 or higher. But the voltage signal is not always the same. Sometimes it's high and sometimes it's low,” said Shinbrot.

Shinbrot has a history of tackling particularly puzzling questions. He even has a page for what he calls “unpublishable research” papers, one of which is on the way identical balloons can gain charge by rubbing against each other, in contradiction to the way electrostatics is usually taught at university. Written in 2006, and rejected by journals at the time, the findings may shed light on his most recent discovery.

Despite his history exploring less mainstream scientific matters Shinbrot was disturbed by what he had found. “Except for the fact that we cannot get these voltages to go away, I would call this 'crackpot physics,' and even as it is, I wish I could hedge my bets, but the voltages are very repeatable, and we have so far failed to account for a spurious influence that might cause them,” he told livescience.com. http://www.livescience.com/43686-earthquake-lights-possible-cause.html

If an explanation can be found for the charge generation during cracking, other poorly understood phenomena may also start to make more sense. This includes the long-puzzling appearance of lightning bolts during sandstorms despite sand's insulating properties.