A ticking time bomb beneath Bangladesh and eastern India :140 million people at risk of massive earthquake

A potentially massive earthquake may be building up under the region beneath Bangladesh and eastern India. Scientists say they have new evidence of increasing strain there, where two tectonic plates underlie the world’s largest river delta, Ganges–Brahmaputra Delta.

The newly identified threat is a subduction zone, where one section of earth’s crust, or tectonic plate, is slowly thrusting under another.

All of earth’s biggest known earthquakes occur along such zones; these include the Indian Ocean quake and tsunami that killed some 230,000 people in 2004, and the 2011 Tohoku quake and tsunami off Japan, which swept away more than 20,000 and caused the Fukushima nuclear disaster.

The findings appear in this week’s issue of Nature Geoscience.

Subduction-zone quakes generally occur where plates of heavy ocean crust slowly dive offshore beneath the lighter rocks of adjoining continents, or under other parts of the seafloor.

Sometimes sections get stuck against each other over years or centuries, and then finally slip, moving the earth.

Scientists knew of the plate boundary in and around Bangladesh, but many assumed it to be sliding only horizontally near the surface, where it sometimes causes fairly large, but less damaging earthquakes in areas that are not as densely populated.

Lead author Michael Steckler, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory says “Assuming fairly steady motion over the last 400 years, enough strain has built for the zone to jump horizontally by about 5.5 meters, or 18 feet, if the stress is released all at once.

If strain has been building longer, it could be up to 30 meters, or almost 100 feet. The land would also move vertically, to a lesser extent. This is the worst-case scenario; in the best case, only part would slip, and the quake would be smaller and farther from Dhaka”

In any case, Bangladesh and eastern India sit atop a landscape vulnerable even to moderate earthquakes: the vast delta of the Ganges and Brahmaputra rivers.

This is basically a pile of mud as deep as 12 miles, washed from the Himalayas to the coast, covering the subduction zone.

In a quake, this low-lying substrate would magnify the shaking like gelatin, and liquefy in many places, sucking in buildings, roads and people, said study coauthor Syed Humayun Akhter, a geologist at Dhaka University.

Bangladesh, the most crowded nation on earth, sits atop what may be one of the planet’s most powerful seismic zones.