Mysterious white and blue lights seen in the sky over Christchurch before and after the earthquake in February 2011 have been explained by researchers in North America.
Writing in the latest edition of Seismological Research Letters, they attribute the lights to an electric charge caused by the tearing apart of the Earth's tectonic plates.
Known as earthquake lights, the phenomenon has been reported for hundreds of years by witnesses in a number of forms including lights running like snakes along the ground and others flickering up from the ground like flames.
The lights occur only in continental rift earthquakes, such as the one experienced in Christchurch, which make up just 5% of recorded tremors.
There are reports of a man seeing the lights two hours before the L'Aquila earthquake in Italy in 2009 and rushing his family outside to safety.
Researchers hope the lights might act as an early warning system.