Perhaps you were like me in thinking that the latest Indonesian earthquake and then the tsunami occurred on a subduction fault. Evidently, there is no subducting fault in that area. Instead it is a jumble of faults mixing together.
I read one story that surmised that the fault was a strike-slip fault. Perhaps the tsunami was caused by an underwater landslide, which does happen. The story concluded that there will need to be some underwater research done to discover the exact cause.
Until then, expect the unfortunate casualty count to continue to rise.