Tsunami concern for Bay of Bengal
Pastor Dale Morgan
Tsunami concern for Bay of Bengal*
Kerry Sieh, Caltech
250,000 people lost their lives in the December 2004 tsunami
[BBC] - The northern end of the Bay of Bengal could be at risk of giant
earthquakes and tsunamis in the coming decades, an Australian study
concludes.
Such events have been thought unlikely there, in contrast to the area
further south where the 2004 tsunami began.
But the new work, published in the journal Nature, has found "compelling
evidence" for tsunami-triggering earthquake activity to the north.
Geologists have said this warning should be taken "very seriously".
The area is densely populated, and more than a million of people could
potentially be at risk.
Releasing pressure
The magnitude 9.2 earthquake that struck off the Sumatran coast on 26
December 2004 and the tsunami it generated killed thousands of people
and left millions homeless.
It stemmed from a geological area known as a "subduction zone".
Map showing fault lines
Here, part of the Indian/Australian tectonic plate was slowly burrowing
beneath a component of the Eurasian plate.
This created stresses in the upper plate, which were violently released
in the form of a "locked-thrust fault" earthquake as it sprung back up,
which in turn triggered the tsunami.
Since then, another stress point has been identified to the east of the
2004 epicentre, but the subduction zone further north along the Myanmar
coast was thought to be of little concern.
But Phil Cummins, lead author on the Nature paper and a geologist at
Geoscience Australia, believes this is not the case.
He said: "I reviewed the geological literature and found the evidence
for a lack of tectonic activity along the Myanmar coast was not compelling."
Historical evidence
Recent GPS data, he said, suggested that the plate boundary was at sea
in this area, hidden below thick layers of sediment.
Dr Cummins said: "Although these GPS measurements are sparse, these show
that there is active deformation near the Myanmar coast that is
consistent with a locked thrust-fault offshore, which is the type needed
to generate tsunami."
Computer simulation of tsunami
A computer simulation shows the havoc a tsunami could wreak
The geologist also looked at accounts of an earthquake that occurred in
the area in 1762, which wrenched up parts of the coast by between 3-7m.
His computer simulation of the quake, which he believes would have
measured magnitude 8.8, showed that a similar event today would have
significant impacts.
"Such an earthquake would generate a large tsunami that could have a
pronounced impact on the Chittagong coast and the Ganges delta," he said.
"The latter region is home to 60 million people living within just 10m
of sea level."
Meanwhile the quake itself could cause major damage to the region's
largest cities, Calcutta and Dhaka. Overall, the simulation suggested
that more than a million lives could be at risk.
'Alarming message'
Professor Richard Arculus, from Australian National University (ANU) in
Canberra, said: "Phil Cummins' warnings should be taken very seriously.
"A few months before the devastating earthquake and accompanying tsunami
triggered off northern Sumatra in late 2004, Phil Cummins published a
perceptive analysis of historic events of this nature in the region.
Disaster planners might need more information than is given in the paper
Kevin McCue
"He warned that countries bordering the Indian Ocean, including the
northern coast of Australia, were at significant risk, and the lack of a
tsunami warning system analogous to that deployed in the Pacific was a
serious issue.
"So his credibility with respect to tsunamigenic earthquakes is
established. "
Kevin McCue, a professor at Central Queensland University (CQU), added:
"The message is alarming, perhaps justifiably, given the unexpected
disaster that followed the great Sumatran earthquake and tsunami of
2004, a disaster of local, regional and global reach."
But he added: "Disaster planners might need more information than is
given in the paper, particularly some quantitative measure of
uncertainties in the science."
Phil Cummins agrees that more work is needed to confirm his analysis,
and suggests this should take place before any drastic mitigation
measures are considered.