Sumatra tsunami: sediment trenches implicated

Hydro International -

The devastating power of the 2004 Boxing Day Sumatran-Andaman earthquake and unusual geological characteristics of the seabed and underlying sediments south of the epicentre contributed to the ensuing tsunami, the deadliest recorded in modern times. The findings come from a US-led team involving researchers based at the UK National Oceanography Centre in Southampton.

The researcher's findings imply that tsunami hazards may be more severe along continental margin regions where trenches contain thick compacted and strong sediment.

"Our findings published in the scientific journal Nature Geoscience will help Earth scientists assess earthquake hazard and the risk of large destructive tsunamis globally," said University of Southampton geologist Dr Lisa McNeill, co-author on the paper.

On 26 December 2004, a powerful ‘megathrust' earthquake struck to the north of Simeulue Island, Indonesia, rupturing part of the Sumatran-Andaman margin plate boundary. The resulting tsunami ranks as the deadliest ever recorded in modern times. It inundated low-lying coastal regions and islands around the Indian Ocean, leading to massive infrastructure damage and loss of life.

Despite the enormity of the earthquake, the size of the tsunami that it generated surprised many geoscientists. Evidence has since emerged that the earthquake rupture propagated unusually close to the deep Sunda Trench, which forms the boundary between the converging Indo-Australian and Eurasian plates in the north-eastern Indian Ocean.

This was unexpected because the weak marine sediments usually found at regions where tectonic plates converge would normally help absorb energy released by an earthquake stopping the rupture progression.

"By investigating the geological characteristics of the margin landward of the Sunda Trench, of the deep seabed and the sediments beneath, we hoped to gain a better understanding of why the earthquake generated such a large tsunami," explained Dr Tim Henstock, also a co-author based at University of Southampton.

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