The quake, which measured 8.9 on the Richter scale according to the US Geological Survey, was the most immense since a 9.2-scale quake hit Alaska in 1964 and the fifth strongest since the beginning of the 20th century.

Wong Wing-tak, senior scientific officer at the Hong Kong Observatory, said the phenomenon, while mercifully rare, was unpredictable, leaving authorities largely powerless to mitigate against its effects.

"Earthquakes likes this, although rare, will occur again. This is part of nature. You cannot predict when and where it will occur again," he told AFP.

"An earthquake that is over 8.0 on the Richter scale usually happens once a year but to reach 8.9 is very rare," he said.

The only quake to register a higher magnitude than the 1964 tremor in the 20th century was one that measured 9.5 in Chile in 1960.

Despite a death toll already surpassing 3,000 and expected to rise steeply, the intensity of the quake was not alone to blame for the number of fatalities.

"The extent of the damage it can cause often depends on where it happens and the structure of buildings," Wong said.

Exactly a year before Sunday's quake more than 30,000 people were killed in a 6.7-scale quake in the Iranian city of Bam, where sloppy builders were blamed for the high toll.

Enzo Boschi, the director of Italy's National Institute of Geophysics, pointed out the impact of Sunday's quake was made significantly worse by the devastating tsunami waves it triggered.

"The situation was compounded by the fact that it occurred at sea, generating a huge wave of water moving at a very high speed," he said.

Tsunamis create a wall of water several metres (yards) in height travelling at speeds of up to several hundreds of kilometres (miles) an hour.

South Asia bore the brunt of the deadly waves, with Sri Lanka particularly hard hit.

By contrast, the Alaskan earthquake of 1964 claimed little more than 100 fatalities, thanks mostly to the state's low density population.

The quake that hit the Japanese city of Kobe in 1995 measured a far smaller 7.2 -- meaning it registered less than one 10th of the intensity of the Indonesian quake on the exponential Richter scale -- but claimed more than 6,400 lives.

No stranger to high-magnitude quakes due to its position straddling the Pacific "Ring of Fire" marked by volcanic and seismic activity, Indonesia is one of the world's most earthquake-prone regions.

The archipelago of some 18,000 islands lies at the collision point of three tectonic plates, resulting in frequent earthquakes and volcanic eruptions as pressure between the massive segments of the Earth's crust is released.

"These quakes are spawned by deformations of the earth's crust, which are in turn caused by a huge build-up of energy," Boschi said.

As energy accumulates and crust deformation reaches a critical level, a fracture in the crust occurs. "The bigger the fracture, the more intense the quake," he said.

Wong described the phenomenon as a fearsome demonstration of the earth's power.

"It's pretty scary and can cause unimaginable damage and loss of life," he said.

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