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