Beneath the Himalayas sleeps a family of faults. For a long time, geologists have been aware that many within this 2,400-kilometer-long (1,500-mile) arc have the ability to decimate cities across some highly populous nations, including Pakistan, India, and Bangladesh.
Bhutan, though, which also lies along the arc, has always been considered unable to experience a significant earthquake. As a new study in Geophysical Research Letters reveals, this isn’t the case at all. In fact, the entire arc is “seismogenic,” in that it’s able to rupture at any point, including beneath Bhutan.
Until now, Bhutan had no detailed seismological records, so a team led by the University of Lausanne decided to investigate. It seemed unusual to them that this country was the only one along the arc to not have experienced a historical quake – except, weirdly, a 6.0M event in 2009.
While attempting to work out how the fault beneath Bhutan had unexpectedly moved, the researchers came across the biography of a Buddhist monk and temple builder by the name of Tenzin Lekpai Dondup. Remarkably, this document described a powerful earthquake in the region that took place in May 1714, one that was followed by plenty of aftershocks.
Frustratingly, though, it did not specify where the earthquake took place.
A costumed monk dances at Bhutan's Tsechu Festival. theskaman306/Shutterstock
However, at the same time, a separate study on the region revealed that some significant vertical fault movement took place in Bhutan that dated back to sometime between 1642 and 1836. Combining this discovery with his own team’s work, lead author György Hetényi – a geophysicist at Lausanne – managed to pinpoint the location of the 1714 quake.
Taking place in western Bhutan, the earth-shattering 7.5 – 8.5M event managed to unzip up to 300 kilometers (186 miles) of the fault line, which represents a whopping 8 percent of the entire arc. As significant as this is by itself, it importantly proves that the entire Himalayan arc can and has experienced powerful earthquakes.
“We are able for the first time to say, yes, Bhutan is really seismogenic, and not a quiet place in the Himalayas,” Hetényi said in a statement.
The Himalayan arc fault network is incredibly complex. The collision of India and Eurasia around 40 million years ago – a titanic tectonic battle that continues to this day – pushed up the crust into the sky, destroying an entire continent as it did so by forcing it down into the fiery mantle. In doing so, a chaotic network of varyingly mobile faults was created.
One of these faults, the Main Himalayan Thrust (MHT), appeared along northern India, which is sliding beneath the Himalayas at a rate of around 2 centimeters (0.79 inches) per year. A 30 kilometer (18.6 mile) stretch of it jutted forwards in April of last year, creating a shallow 7.8M quake that rocked Nepal and killed more than 23,000 people.
Another major regional fault, a megathrust beneath the Indo-Burman mountain ranges – the boundary between the Indian and Eurasian plates – is due to slip in the near future after laying dormant for around 400 years. When it does, it will produce at least a 9.0M tremor that threatens the lives of 140 million people mainly living in Bangladesh.
Knowing that the entire Himalayan arc network is able to slip is decidedly disconcerting. It will never all slip at once, of course, but the sheer scale of the active zone is hard to fathom. For comparison, the San Andreas Fault, which is soon to unleash the so-called “big one” that will devastate much of California, is 1,300 kilometers (800 miles) long.
The Himalayan arc is nearly twice that size.
The Himalayas. Olga Danylenko/Shutterstock