Indonesian earthquakes: just foreshocks of the Really Humongous One?

Kerry Sieh thinks the M8.4 and other recent earthquakes off the coast of Sumatra might be essentially foreshocks to a larger, M9+ earthquake:

"No one can say whether it will be in 30 seconds or 30 years," he said. "But what happened the other day, I think is quite possibly a sequence of smaller earthquakes leading up to the bigger one."

(Quote from yahoo's news, but I've seen essentially the same report other places.)

He's published a lot of stuff about the Sumatra earthquakes since 2004, and I haven't read any of it, so I'm not sure which of several reasons he may have for his statement. (He has worked out the paleoseismic history of the subduction zone, so he may be thinking about recurrence intervals - typical times between major earthquakes on a given fault zone. He could be thinking about seismic gaps - areas of the fault that haven't had as many earthquakes, and are therefore probably more prone to slip. He could be thinking about the M 8.4 earthquake as a foreshock - a smaller earthquake that precedes a larger earthquake. He could be thinking about stress changes as a result of the 2004 M9 earthquake - something similar to the work that's been done on the North Anatolian Fault in Turkey, except on a subduction zone.)

[Edit: I suppose Sieh could also be making a far more basic point: the subduction zone is capable of larger earthquakes. The news may simply be a good opportunity to remind people of that fact, just like little earthquakes in LA or SF are a good opportunity to remind people that California is earthquake country.)

It feels like studies of earthquake mechanics are on the verge of really understanding the process better. It's exciting... though for the sake of Sumatra and people living beside the Indian Ocean, I hope Sieh is wrong.