From Scientific American: Indonesian Tsunami Was Powered by a Deadly Combo of Tectonics and Geography. The magnitude 7.5 earthquake that touched off the tsunami occurred amid a complex puzzle of tectonic plates.
Thanks to Ian McLean of New Zealand for this citation. He says that NZ also has similar tectonic conditions. Here are some of his observations about the seismic conditions and risk in New Zealand.
What I found particularly interesting was the fact that the earthquake occurred in a transition zone. To the west of this zone one plate subducts, and to the east of the zone the plates abut pushing up mountain ranges.
The configuration is similar to the zone in New Zealand where the Kaikoura sequence of earthquakes occurred.. To the north the Pacific plate subducts the Indo-Australian plate; and to the south the plates abut, pushing up the Southern Alps.
In the transition zone is a complex jumble of faults. Several of these ruptured sequentially during the Kaikoura sequence. The damage was unexpectedly severe, especially in Wellington.
But NZ still awaits with apprehension earthquakes along the plate boundaries to the south and north of the transition zone. To the south , the Alpine fault has reached its mean return period. In the north, knowledge about the HIkurangi subduction zone was sparse, but substantial research is now being done.