I have to admit, I've never heard of this before - but Earthquake Lights, or "Lightning", is a well documented phenomena.
When I was in the big Christchurch quake two Saturday's ago I noticed three or four brilliant blue flashes that lit up the sky (but didn't light up the city itself, as normal lightning would do). My first instinct was that it was power transformers exploding.
However on reflection I realised the lights were simply too bright and lit up too much of the night sky.
I had a few comments posted here and at WeatherWatch about the lights being caused by the quake itself. So I decided to find out - I called GNS (Geological and Nuclear Sciences) in Wellington.
Dr Martin Reyners was the Seismologist I spoke to and he indeed confirmed that what I saw was most likely a direct result of the earth shifting. Oddly, they hadn't had any other eyewitness reports. However I'm now starting to hear via my Twitter account that others saw it too. I suppose most people didn't have a 7th floor view of Christchurch at the time the quake struck so I was in a prime viewing position.
Dr Reyners says with shallow quakes this has been widely documented.
See a video of something similar to what I saw.
Up until the 60s it was widely dismissed however during the Matsushiro earthquake swarm in Nagano, Japan between 1965 and 1967 scientists finally acknowledged its existence following a number of documented photographs.
In the big Inangahua quake in 1968 (also 7.1) locals reported seeing flashes of light. Similar reports came from Peru and Chile in recent times.
Dr Reyners says there are lots of theories but no one explanation, however heat from the fault zone and gases igniting have been ruled out.
There are some theories it may have something to do with the "sparking" effect of rock grinding against rock.
Other theories have also been placed on Wikipedia: "Another possible explanation is local disruption of the Earth's magnetic field in the region of tectonic stress, resulting in the observed glow effects either from ionospheric radiative recombination at lower altitudes and greater atmospheric pressure or as aurora" says the website.
It goes on to say there is also debate in the scientific community regarding radon as a possible precursor to some earthquakes - so another theory is that glowing clouds might be light emission produced by ionisation or plasma-chemical reactions.
What amazes me is if you go to YouTube or Google and search Earthquake Lights it brings up conspiracy theories, much like the jet trail ones. If you get past that rubbish you'll find the actual scientific community discussions which really are quite fascinating.
One thing this research has fone for me is given me a better perspective on the depth of our planet. Something that happened 10kms underground....two and half times the height of Mt Cook - lit up the sky over Christchurch a number of times on Sept 4th at 4:35am. It's a sneak peak into the simply MASSIVE amount of energy inside this planet we live on.