Thoughts on 2004, december 26th Sumatra earthquarke

Just after the big earthquarke which was at the origin of the devasting tsunani wave near Sumatra, we started to hear here and there that the energy released by the quake was sufficient to make the earth rotation axis oscillate. I'm not an expert in geophysics, then I had no background to guess what would be the amplitude of the oscillation if any. But I'm an astronomer. And astronomers have a powerful and simple tool to measure such axis mouvement if it is big enough, of course: the stars! The are fixed regarding such oscillation.

If an earth-based telescope is performing an image of a star field during such an event, if the axis of the Earth oscillates, it might be possible to see and measure the oscillation looking at some little trails left by the stars. I would say that such a movement can be observable up to some tens of arcsecond, depending on sky quality, seeing, instrument and so on.

Beside the annoucement by the media of such axis oscillation, with some eccentric numbers, I've found a prediction which seems more reliable: according to some models, the amplitude of the oscillation would have been of 0.8 milliarcseconds. Such a value is by far too small to be measured "astronomically".

Nevertheless, it would be interesting to do such a measurement, even to put some constraint (upper limit) on this kind of model. The earthquake took place on Sunday, December 26, 2004 at 00:58:53 (UTC). I've tried to ask some information on the expected delay time of the axis oscillation after the quake, but got any reply. My naive guess would be of the order of 10 minutes after the quake (assuming a velocity of sismic waves of 10 km/s). Then, if around 01:10 UTC on december 26th, somebody was doing a CCD exposure of the sky, it might be interesting to check it for any strange (but small) star trails. This concerns all observatories (professional of amateur) for which it was dark time, from India to United States. Note that it was a full moon night.

Guillaume Blanc ()