Mysterious lightning flashes that appear to precede earthquakes could be sparked by movements in the ground below, US scientists say.
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"Our first suspicion was this has got to be a mistake. There must be something stupid we are doing," said Professor Troy Shinbrot, of Rutgers University, New Jersey.
"We took a tupperware container filled with flour, tipped it back and forth until cracks appeared, and it produced 200 volts of charge.