Asia’s inevitable great quake could be much worse than Haiti’s

The horror in the aftermath of the Haiti earthquake is undeniable. But it is by no means the worst seismic devastation that nature can dish out. A far more devastating quake — one that could possibly kill millions of people — is not only probable but possibly inevitable in one of the most densely populated regions of the world.

That region is the arc of densely populated territory south of the Himalayan mountain range. It includes some very large cities, including Islamabad, Delhi and Dhaka, and a host of other smaller towns and villages.

The risk arises for the same reason that the earthquake rocked Haiti, and the same reason that the densely populated San Francisco Bay region is at great risk from an earthquake along the Hayward fault: The Earth’s tectonic plates are in constant motion, and in some places, they do not slide smoothly past each other. They become locked for a time until enough strain builds up, causing a sudden rupture — and an earthquake.

Right now, plate movements are causing the subcontinent of India to ram into the underbelly of Asia. Like the hood of a car crumpled up in a collision with a larger SUV, the Indo-Asian tectonic collision has crumpled part of the Earth’s crust, raising up the Himalaya, Earth’s highest mountain range. This collision has been occurring over geologic time, meaning millions of years. Even so, India and Tibet are converging at a rate of about 20 millimeters, or just shy of an inch, each year, according to research by Roger Bilham and Peter Molnar, earth scientists here at the University of Colorado, and V. K. Gaur of the Indian Institute for Astrophysics,  published in the journal Science in 2001. (Subscription required.) That may seem like a tiny amount, but it adds up: India converges on Tibet at a rate of two meters per century.

The problem is that India doesn’t slip smoothly beneath the Tibetan Plateau in all places. Instead, India pushes and pushes against Tibet until the strain builds up enough for a massive rupture to occur — triggering a great earthquake. Such earthquakes occurred six times between 1800 and 1950, according to Bilham, Molnar and Gaur. But large portions of the arc of territory stretching along the Himalayan mountains did not rupture during this period.

From their Science paper:

Although the major earthquakes that have occurred along the Himalaya since 1800 differed in dimensions, there is no doubt that they destroyed vast regions along the front of the Himalaya. More important today, however, is that less than half of the Himalaya . . . has ruptured in that period.

In essence, this means that more than half of the Himalayan front is overdue for a great earthquake.

The researchers divided the Himalaya into 10 regions, with each one about 220 kilometers long. They found that in six of those regions, the land has the potential to shift suddenly by more than four meters in an earthquake. And in large areas, no great earthquake has occurred to relieve the strain since 1700, “suggesting that the slip potential may exceed 6 m in some places,” the researchers wrote.

Moreover, they could not rule out the possibility that some parts of the Himalaya have not ruptured to relieve the strain for up to 700 years. And that implies a shift in the landscape by as much as 10 meters.

To understand what that means, imagine a stretch of territory 100 or more miles wide suddenly shifting northward by about 30 feet. The resulting earthquake would almost certainly be much more devastating that the one that occurred in Haiti.

Devastation from an earthquake depends not only on its magnitude. It also depends, of course, on the density of population and the quality of construction. And this region of the world is home to millions of people, many of whom live and work in substandard structures.

From the paper in Science:

Today, about 50 million people are at risk from great Himalayan earthquakes, many of them in towns and villages in the Ganges plain. The capital cities of Bangladesh, Bhutan, India, Nepal, and Pakistan and several other cities with more than a million inhabitants are vulnerable to damage from some of these future earthquakes.

Based on what happened in the aftermath of the 2001 Bhuj earthquake in India, Bilham and Molnar estimated that a great Himalayan quake could kill 200,000 people. And possibly many, many more than that: “Such an estimate may be too low by an order of magnitude should a great earthquake occur near one of the megacities in the Ganges Plain.”

An order of magnitude higher than 200,000 yields a death toll in the millions.

Today, about 50 million people are at risk from great Himalayan earthquakes, many of them in towns and villages in the Ganges plain. The capital cities of Bangladesh, Bhutan, India, Nepal, and Pakistan and several other cities with more than a million inhabitants are vulnerable to damage from some of these future earthquakes.

So Haiti may well be just a prelude of what’s to come — a profoundly devastating mega-quake.