Bangladesh earthquake warning: 140 million people may be at risk, scientists say

Peter Hannam, The Age, July 12 2016

As many as 140 million people in Bangladesh may be at risk from a huge earthquake as pressure builds beneath the surface of one of the world’s most densely populated nations, US and Bangladeshi scientists say.

Sediment flows from the Ganges and Brahmaputra rivers have layered parts of the country with as much as 20 kilometres of sand and mud, masking until now the extension of the same fault line that triggered the 2004 Sumatra tsunami and killed 230,000 people.

Researchers say a major earthquake risk could be building under Bangladesh, one of the world’s most densely populated nations.

“The fault is entirely in the sub-surface,” said Michael Steckler, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of a paper published this week in Nature Geoscience. “It’s been suspected but we haven’t had the data to prove that [the pressure] is actually been building up.”

Data collected since 2004 by Professor Steckler’s team has found that a juncture between major tectonic plates in the region is locked and loading up with stress.

Measurements found convergence of tectonic plates at the rate of 13-17 mm per year “on an active, shallowly dipping and locked megathrust fault”, the paper said.

That build-up has the potential to trigger major shifts in land and also an earthquake with a magnitude of between 8.2 and 9.

“We can see the strain building up, we can see the motion of the plates but we can’t estimate when something might happen,” Professor Steckler told Fairfax Media, adding that the build-up had been going on for at least 400 years and perhaps as long as 2000.

“It would certainly be one of the largest [recorded quakes],” he said. “I suspect it might be at the lower end [of the 8.2-9 scale], but I can’t rule out a really large one.”

Scientists can’t tell when the next major quake will strike nor where the rupture in the fault will be the most severe. However, Bangladeshi’s location mostly on the river delta of the giant Ganges-Brahmaputra Delta makes the bulk of its 160 million population particularly vulnerable, should a large one occur.

Professor Steckler said a 250 kilometre by 250 kilometre region–including the capital, Dhaka, a megacity with a population of 15 million–is of significant risk.

This area is home to about 140 million people, and sits atop deep sediment that could liquefy in many places in the advent of a big quake. Whole buildings and infrastructure could sink into the sand and soil.

Buildings might “not even break, but literally fall over because the soil loses solidity”, he said.

Syed Humayun Akhter, from Dhaka University, said the capital could become “totally a dead city … it will be really devastating”.

“All the natural gas fields, heavy industries and electric power plants are located close to potential earthquakes, and they are likely to be destroyed,” Dr Akhter said. “In Dhaka, the catastrophic picture will be beyond our imagination, and could even lead to abandonment of the city.”