A megathrust fault could be lurking underneath Bangladesh, India and Myanmar, exposing one of the most densely populated regions in the world to the risk of a large earthquake, according to new research published in Nature Geoscience.
A new GPS study measuring tiny ground movements since 2003 in the south Asia region has found strong evidence suggesting that a large tectonic fault beneath Bangladesh and east India is seismically active.
The team, consisting of scientists from the USA, Singapore and Bangladesh, calculate that the megathrust fault could be accumulating strain energy at rates of about 15 mm per year.
Importantly, the researchers believe that the fault is “stuck” and has been storing energy for more than 400 years without a major earthquake; since the Mughal conquest of Bengal and the establishment of Dhaka as the Bangladeshi capital in the 1600s.
An earthquake occurs when the stresses become large enough that it causes the fault to break and releases all the stored energy. The 400 years of energy accumulation at 15 mm per year could result in a devastating magnitude 9 earthquake, similar in size to the Japanese quake that destroyed huge sections of the country’s northeastern coast in 2011. Such an event would have enormous consequences for more than 140 million people living within 100 km of the megathrust in Bangladesh and India.
The tectonic activity of south Asia is a consequence of the collision of the Indian subcontinent with Asia, a process that began nearly 50 million years ago and is still occurring today. This monumental collision resulted in the uplifting of Tibet and the formation of the Himalayan mountain range. Over millions of years these mountains have been slowly eroded and deposited their rich soils onto the Bangladeshi plains by a network of giant rivers. The thick sediments have made the Bangladeshi plains some of the most agriculturally productive in the world.
While the sediments can take up some of the energy along the newly proposed fault, they’re not especially stable, particularly around the rapidly developed eastern outskirts of Dhaka. If a major earthquake strikes, the sediments could even amplify the seismic waves, causing further destruction.
“Dhaka’s basically like building a city on a bowl of Jell-O [jelly],” says Steckler, lead author of the new study, implying that even small earthquake shaking could be amplified by the sediments.
The Savar building collapse in 2013, which resulted in over 1100 deaths, showed the world that building codes in Bangladesh are not strictly enforced. If buildings are collapsing on their own, it is a terrifying prospect to consider what would happen during an earthquake. The lack of preparedness is clear and it is essential for the Bangladeshi government to make long-term changes to promote greater seismic awareness and stricter enforcement of building codes.
 The original paper: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2760.html