Kathmandu was a geological time bomb


The 7.9 magnitude earthquake that hit Nepal and north India today, causing at least 1,500 casualties and widespread damage in Kathmandu, with the death toll rising all the time, was only too predictable as Cosmos reported in July last year - see Kathmandu's earthquake nightmare.

As Kate Ravilious wrote then

Earthquakes are a fact of life in Nepal. India is slamming into Asia at a rate of four centimetres a year and the strain that accumulates in the tectonic plates periodically releases itself in the form of earthquakes. This collision of continents has forced up the vast Himalayan mountain chain as the Indian plate slides beneath Asia. Tremors of magnitude 4 or 5 happen more than 10 times every year. But the real worry is the “great” earthquakes – magnitude 8 or more – that occur every century or so as strain in subsections of the fault up to 200 km long suddenly and violently releases.

Since the last great quake – a magnitude 8.4 – in 1934 the population of Nepal has risen fivefold.

Geologists such as Paul Tapponnier have been working for years trying to understand the mechanics of the geology of the region, convinced that, if they can, they will better be able to predict major new earthquakes. But the geology is tricky.

As Kate wrote last year

Despite decades of searching no one had ever managed to find the rupture from the 1934 quake, leading many geologists to conclude that Nepal’s earthquakes are “blind” – the movement occurring deep underground but never quite slicing all the way up to the surface.
But Tapponnier was never convinced by that theory. “For me the idea of a ‘blind’ great earthquake is a paradox. We don’t find them in other parts of the world so the theory seems very strange.” It was a tantalising problem, the solution to which had potentially tremendous rewards for Nepal. “If a fault is blind then there is very little you can do except sit and wait for the earthquake – but if you know exactly where the earthquake tore the ground you can really start to prepare and reduce risk,” he says. In 2006, after a case of high-altitude pulmonary oedema made it dangerous for Tapponnier to continue working on the Tibetan plateau, he decided to descend to the plains of Nepal and try to solve the “blind” earthquake puzzle.

He, and other scientists like him, warned that another major earthquake was overdue. In fact Tapponnier anticipated a major quake in exactly the location in which the current earthquake happened.

“The place I’m worried about now is central Nepal. I suspect that this central segment of thrust produced the great earthquake of the 14th century, which damaged much of Kathmandu. If that segment has a consistent recurrence time then the next great quake could be due there very soon,” he said.

  1. http://www.theguardian.com/world/2015/apr/25/nepal-hit-by-strong-earthquake
  2. https://cosmosmagazine.com/earth-sciences/kathmandus-earthquake-nightmare
  3. http://www.kateravilious.net/
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