Earthquake weather - we've all heard it before, but what is it exactly? To many it's an eerie stillness that precedes a large earthquake and there are many documented cases of it.

Personally I was in the 1987 Edgecumbe earthquake, which was incredibly violent and my memories of it are burnt into my mind forever. One of those memories concerns the weather on that March day. I can distinctly remember the eerie sky, cloudy but not completely overcast, dead still - not a breeze at all. And it was mild, luke warm really. The calmness is the most distinctive part of that memory.

Again, last Saturday in Christchurch, I landed in a wintry southerly, just 2 degrees and raining. By night time the skies had cleared. It was cold, yes, but dead still and cloudless. When the quake struck at 4:35am I remember noticing the stars as I looked out the window. I don't know why I noticed them, I just did.

The famous Napier earthquake had clear blue skies and again, it was dead calm. Same with the big LA earthquake, and the San Fran earthquake.

Haiti had clear skies. And from memory so too did Conception, Chile.

The belief behind earthquake weather is that pockets of air trapped in underground caves shifts around due to the weather on the surface of the Earth. The bigger the shift, the bigger the quake. (The USGS website states that, in the 4th century BC, Aristotle suggested that this is how earthquakes formed.)

However scientists say there is no proof that this exists and maintain that earthquakes can happen in any weather in any season at any time of the day, month or year.

I have to admit, I tend to agree, however the big earthquakes, the ones that make the news, do seem to happen on calm, clear, days. Coincidence or not?

An article in Wikipedia caught my attention. It says Geologist Russell Robinson has described earthquake weather as one of the more common pseudoscientific methods of predicting earthquakes.

A modern theory proposes that certain cloud formations may be used to predict earthquakes, however, this idea is rejected by most geologists.

The article says geologists maintain that there is no connection between weather and earthquakes. They are the result of geologic processes within the earth and can happen in any weather and at any time during the year. Which makes sense.

It's not for all earthquakes. The aftershocks following Edgecumbe were accompanied by thunderstorms. But for those big, main event quakes there does seem to be a weird coincidence.

Of course earthquakes happen a long way underground. The one in Christchurch was shallow, just 10kms. That's still 2 kms further than Mt Everest reaches. It would seem utterly impossible for something 10kms underground, let alone 50 or 200kms underground, to be affected by weather on the surface of our planet.