Recent seismic activity in the region has piled dangerous levels of stress onto a section of the Sunda trench fault zone west of Sumatra. This makes a large earthquake there far more likely and could trigger another devastating tsunami.
The warning comes from a team of seismologists at the University of Ulster in Coleraine. Professor John McCloskey, who led the research, said: "This is a very scary event we're concerned about. The potential for a devastating tsunami from it is significant and real. I hope it doesn't happen, but the indications are really strong that it will, maybe even soon."
Giant earthquakes can raise stress in surrounding rocks, making other seismic slips more likely. In March the Ulster group looked at the effects of the Boxing Day event and predicted another giant earthquake would strike the region. Less than two weeks later, on March 28, an adjacent region of the fault gave way. The magnitude 8.7 earthquake killed an estimated 2,000 people, mainly on the island of Nias.
The Ulster team has now used the same technique to assess the aftermath of that second quake. Their analysis shows stress in the region to the south of the March 28 rupture has increased by up to 8 bar, priming it for a massive megathrust quake where one tectonic plate slips beneath another.
The scientists cannot predict exactly when the next earthquake might strike, but say local people ought to be prepared. There are plans to deploy sensors to detect tsunamis throughout the Indian Ocean, but no system is yet in place.
The Mentawai islands face the greatest threat. Although stress increases are higher near the Batu islands, an earthquake last struck there in 1935. The Mentawai section of the fault has not slipped since 1833, when records show the resulting giant earthquake caused a large tsunami.
Prof McCloskey said his calculations suggest the risk of another massive earthquake is now greater than it was before March 28. "There are several indications that this one looks like a stronger interaction than the last. The actual stresses we measure are more or less the same but the ripeness of the fault now is of real concern." The recent increase in the number of small and medium earthquakes in the area is also ringing alarm bells.