I have not read Sieh's comments in detail nor have I read his paper (guess I should do that rather than post here....). But, I went to a discussion of the earthquake yesterday with lots of Big Shot seismologists. That was a non-public discussion and I don't think they would appreciate my posting what was discussed, (I'd have to ask each person to post what they said). But, I think I posted here a couple days ago that, after looking at the modeled size of the quake, there is plenty of room to have one or more Great Quakes.....and it has been a long time since the last ones (1833?), and I already posted here the other day that 1 m of slip builds up every 20 years...so there are already over 8 m of slip accumulated and possibly much more. And, John can comment....but this quake probably stressed the next section on either side, so that the date of the future quake has been advanced.

When I first was posting after the quake I thought that this past quake was an exceptionally rare quake and it could be 1000 years or more until the next one that could send a mega tsunami across the Indian Ocean. I no longer think that.

Qualification: I don't have any information that everyone else doesn't have, I am not a seismologist, but I do know what I'm talking about. The next Great quake beneath Sumatra, farther south, or on the plate boundary farther north could be decades or 100(s) of years away. Or, it could be any time. So, there is some urgency to take steps like tsunami warning system and, Petra, education of the local residents to get away from the coast after they feel a long duration earthquake, or if they see the sea behaving strangely.
Chris