This is an example of how tsunami prediction is basically impossible without specific sensor buoys...an 8.7 is a really truly big quake and quakes of that size have generated HUGE tsunamis...
But many really big quakes, even underwater subduction quakes, don't generate a tsunami at all.
The area might have dodged the tsunami bullet.. this time.
AP:
"It seems this earthquake did not trigger a tsunami. If it had, the tsunami would have hit the coastline of Sumatra by now," said Prihar Yadi, a scientist with the Indonesia Geophysics Agency. "And if there's no tsunami on the coastline near the epicenter of the quake, there will not be one heading in the other direction."
The energy from the quake was generated in a southerly direction, said Eddie Bernard, a tsunami expert and director of the Pacific Marine Environmental Laboratory in Seattle, in an interview with CNN. That direction is away from area struck on Dec. 26.