Research sheds light on quake mystery
A dark hole of knowledge about strange lights seen during the 2011 Christchurch earthquake has been illuminated by new research out of North America.
Many witnesses recounted seeing white and blue lights in the sky before, during and after the quake.
Cameras near Lyttelton Road Tunnel and Princess Margaret Hospital were also reported to have caught blue flashes after the quake.
Researchers writing in the latest issue of Seismological Research Letters have found this phenomenon was caused by a type of earthquake in which one of the Earth's tectonic plates was pulled apart, creating a rift.
The tension during this process created an electronic charge, which turned into light when it reached the surface.
Earthquake lights have been seen worldwide, with some only at ground level and others being projected into the sky.
Pedestrians during a 2009 earthquake in the Italian city of L'Aquila reported fire flickering from the stone pavement of their town's historical city centre.
This was one of 65 of the best-documented earthquake light events in North America and Europe the researchers studied.
They found 97 per cent of the events happened during continental rift earthquakes, similar to the ones that hit Christchurch.
Those types of earthquakes made up just 5 per cent of all quakes, as most quakes occurred when two plates collided, not when one plate was pulled apart.
They also happened in areas not known for earthquake activity and could be used as an early warning system, Canadian geologist Robert Theriault said.
He pointed to the account of a L'Aquila resident, who, after seeing flashes of light from inside his home two hours before the main shock, rushed his family outside to safety.
"It's one of the very few documented accounts of someone acting on the presence of earthquake lights.
"Earthquake lights as a pre-earthquake phenomenon, in combination with other parameters ... may one day help forecast the approach of a major quake."
The statistics were striking and unexpected but it was not yet known why these types of earthquakes were the main cause of the lights, Theriault said.