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Scientists warn of Bangladesh earthquake time bomb


A previously unknown subduction zone deep beneath eastern Bangladesh has been building up strain for centuries. Bill Condie reports.


Dhaka, the capital of Bangladesh, is a hive of multistory buildings housing around 17 million people in the greater Dhaka area. But can it survive a 'megathrust' earthquake beneath the Indo-Burman Ranges?
Inkiad Hasin / Getty Images

Bangladesh is sitting on a time bomb, with scientists warning that increasing strain at the meeting of two tectonic plates beneath the country could lead to a catastrophic earthquake.

The area is a subduction zone where the Indian plate is slowly thrusting under the Sunda plate.

It is an extension of the tectonic boundary that ruptured under the Indian Ocean in 2004, setting off the tsunami that killed more than 230,000 people.

Bangladesh, Myanmar and eastern India (all near top) are bisected by an extension of the tectonic boundary that ruptured under the Indian Ocean in 2004, killing some 230,000 people. Known quakes along the boundary's southern end are shown in different colours; the black sections nearer the top have not ruptured in historic times, but new research suggests they could.
Michael Steckler / Lamont-Doherty Earth Observatory

While the plate boundary in Bangladesh is well-known, it has previously been thought of as relatively harmless with movement close to the surface.

But new research published this week in Nature Geoscience suggests subduction is taking place deep below the surface, with huge stresses building up where the plates meet.

Since 2003, American and Bangladeshi researchers have been tracking tiny ground movements using GPS devices linked to satellites. That has shown eastern Bangladesh and part of eastern India pushing diagonally into western Myanmar at around 46 millimetres a year.

The authors say it is an "underappreciated hazard."

“Now we have the data and a model, and we can estimate the size.”“Some of us have long suspected this hazard, but we didn’t have the data and a model,” lead author Michael Steckler, a geophysicist from Columbia University is quoted as saying.

And that could be huge. It has been at least 400 years with no quake, suggesting the strain has been building all that time.

Steckler says the quake, when and if it comes, could be larger than 8.2, and reach a magnitude of 9.

“We don't know how long it will take to build up steam because we don't know how long it was since the last one,” he said.

Bangladesh lies on the far eastern edge of the giant Indian plate, that comprises the subcontinent and much of the Indian Ocean. It has been thrusting northeasterly into Asia for tens of millions of years. It is responsible for the creation of the Himalayas as well as the devastating earthquake that hit Nepal in April 2015.

The region around Bangladesh has been subject to many earthquakes over the years but geologists assumed there was no subduction under Bangladesh itself.

But the current researchers say the signs have been there all along in the form of parallel north-south ranges of mountains “draping the landscape, like a carpet being shoved against a wall”.

Bangladesh is unprepared for such a disaster with poorly enforced building codes and a huge densely packed population.

Scientists say they will continue to monitor the situation, with New Mexico State University planning to deploy 70 seismometers across Myanmar in 2017, to get a better image of the subducting slab.

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Bill is head of publishing at The Royal Institution of Australia and former publisher of Cosmos.
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