Large aftershocks go at far north as about 1.6 deg south, so only about 200 km +/- between the rupture zone of yesterday and that of 2005. Someone could come up with a more precise number. That might be enough for about another M8.0 if it were to go in one chunk, but not much bigger than that. Caution...I'm not a seismologist and am just putting this up for discussion. It is not a prediction. I'm not even looking up the information on 2005.
Chris