Is Bhutan’s earthquake hiatus over?

Bhutan, the enigmatic country wedged between northeastern India and Tibet is probably best known as the home of the ‘happiest’ people on the planet.

One thing the Bhutanese are certainly happy about is that their country, which lies within the seismically active and earthquake-prone Himalaya, has not experienced a large earthquake for more than 300 years.

The Bhutanese traditionally believe the movement of a giant underground spirit called Naka causes earthquakes. However, Bhutanese Masters student Phuntsho Pelgay, working with researchers from the University of Melbourne’s School of Earth Sciences, looked at movement of the earth beneath Bhutan and discovered the country’s recent low seismic activity is probably just plain luck. And he said the country should prepare for the possibility of an earthquake of similar magnitude to the devastating 2015 Nepal earthquake.

In Bhutanese culture Naka feeds on dung balls, and therefore the dung beetle is highly valued for its role in delivering these carefully crafted balls to Naka’s underground home. As long as Naka eats these dung balls, he remains sedentary and the earth remains stable.

At a young age, a curious Phuntsho Pelgay went in search of Naka. He started digging and after some time, he had a very deep hole – yet no dung beetles or dung balls, and no spirit Naka.

“If Naka isn’t there, then what on earth causes earthquakes?” he asked.

And so, Mr Pelgay’s interest in earthquakes and tectonics began. With the support of an Australia Awards Scholarship this interest led him to complete a Master of Science at the University of Melbourne, where he studied the potential for the Bhutanese Himalaya to experience severe earthquakes, under the supervision of Professor Mike Sandiford.

The Himalayas and Tibetan plateau began forming over 50 million years ago. The Himalaya is a product of the ongoing collision and convergence of the Indian and Asian continental plates. This is why the region is growing upwards and is so susceptible to large earthquakes. The historical distribution of seismic strain release within the Himalaya has been uneven and the Bhutan Himalaya has experienced low seismic strain release.

A seismic gap is a segment of an active fault that is known to produce severe earthquakes, but has not slipped in an unusually long time. Previous studies have suggested that the Bhutan seismic gap occurs because strain is distributed south into growth of the Shillong Plateau in India.

To analyse the seismic gap, Mr Pelgay, Professor Sandiford and a team of geologists from the School of Earth Sciences traveled to the Bhutanese Himalaya to gather geological samples.

This was the start of a project that Professor Sandiford hopes will lead to further collaborations within Bhutan.

“Our team hopes to explore new opportunities for joint geological mapping with the Bhutanese government similar to the previous work that we did in Timor Leste,” Professor Sandiford says.

After they returned to Melbourne, the samples were analysed in the lab and the researchers looked for deformation and landscape responses across timescales ranging from one thousand to one million years.

The results from these analyses suggest that activity at the Shillong Plateau has little direct effect on how strain is distributed along the eastern Himalaya.

“The propensity for large to great earthquakes in the Bhutanese Himalaya is similar to the rest of the mountain range,” Mr Pelgay said.

“This implies that the Bhutan seismic gap has the potential to produce an earthquake as big as the recent 7.8 magnitude in Nepal, which killed more than 8,000 people.”

Mr Pelgay has now returned to Bhutan and is working with the Bhutanese Government in the Department of Geology and Mines to continue his research and help his country better prepare for future earthquakes.

Banner image: Matt Wood