Massive Myanmar quake, tsunami could kill millions around Bay of Bengal

PARIS, (AFP) - The northern tip of the Bay of Bengal, home to tens of millions of people, faces a potential double whammy from an earthquake and tsunami, a scientist warned on Wednesday. He says the peril does not appear to be immediate but says there are many unknowns and further work is needed to quantify the risk.

Quake experts today fret about a stress point just east of where the December 26, 2004 temblor occurred near the Indonesian island of Sumatra, killing some 220,000 people. The risk of another giant event at this spot is high, they fear. But Phil Cummins of Geoscience Australia says another danger lurks to the north along the coast of Myanmar and Bangladesh, in a so-called subduction zone -- where one part of the Earth's crust is slowly diving under another.

A vicious "locked-thrust" fault, of the kind that unleashes tsunamis, runs parallel to the shore in similar fashion to the Sumatra fault, he believes. It has been overlooked because the last big quake there was nearly two and a half centuries ago, and the fault lies hidden under seabed sediment up to 20 kilometres (12 miles thick), he contends.

"This is the type of earthquake that could generate a large tsunami which could impact the densely-populated Ganges delta," he said in a phone-in conference with reporters. "The earthquake itself could cause much damage in Chittagong and perhaps significant damage even in Dhaka and Calcutta [Kolkata]... very large populations are potentially at risk."

On April 2, 1762, a large earthquake hit the Arakan coast of Myanmar, wrenching up parts of the coast and several offshore islands by between three and seven metres (10 and 23 feet). Anecdotal evidence suggests that this also caused a tsunami. A family history, recounted to the commander of a British ship that visited the remote area in 1841, described how "the sea washed to and fro several times with great fury, and then retired from ground."

At Dhaka, now the bustling Bangladesh capital, the river rose suddenly and "hundreds of large country boats were driven ashore or lost, and great numbers of lives lost with them." Cummins, whose paper is published in Thursday's issue of Nature, believes the fault ruptured along 500 kilometres (310 miles), an exploit consistent with an earthquake of 8.8 magnitude.

His computer simulation of the event says the tsunami would have reached a maximum height offshore of 2.5 metres (8.1 feet). Further work, harnessing precise knowledge of the ocean bed topography, is needed to estimate its height once it hit the shore.
In addition, GPS sensors on the ground suggest that the fault is still tectonically active, with movement of around 23mm (0.9 inches) per year, says Cummins.

"It would take an additional 200 years from now for the stress to build up to its pre-1762 levels, but on the other hand, the rupture could occur in smaller earthquakes" whose timing is unknown, he said. Around 60 million people at the Ganges-Brahmaputra delta live within 10 metres (32.5 feet) of sea level, many in quake-vulnerable homes, says Cummins.

More than a million lives may be at risk from a repeat of a 1762-level event, he says, but admits that this is little more than a guess."We need further geodetic measurements to measure possible stress buildup along the coast of Myanmar and Bangladesh and further geological studies in this area to detect traces of the 1762 and earlier earthquakes and tsunamis," he adds.