AS INDONESIA prepares to mark the fourth anniversary of the Boxing Day tsunami that killed more than 200,000 people, new scientific findings are painting a grim picture.

An earthquake potentially larger than the one that triggered the 2004 tsunami is threatening off Sumatra, researchers from the Nanyang Technological University (NTU) said on Thursday.

'What we are now trying to understand is how close it is to happening,' said Professor Kerry Sieh, director of the university's Earth Observatory of Singapore.

Sumatra lies above one of the most active earthquake sites in the world known as the Ring of Fire.

Using satellite and field data collected after an earthquake in September last year near the island's coast, researchers found something ominous.

While the tremor released some of the tremendous pressure created by the movement of the Earth's tectonic plates, a large amount of tension remains.

Researchers say that is a recipe for a major quake that could be larger than the 9.2- magnitude tremor in the Indian Ocean that unleashed the 2004 tsunami.

But the scientists are not sure when or where the earthquake will strike, making it impossible to predict whether the fallout will be as devastating as in 2004.

About 20 people died in an 8-magnitude quake last year which uprooted nearby coral reefs, lifting them up to one metre above the ocean's surface.

Read the full story in Friday's edition of The Straits Times.