New 7-year study shows Bhutan is due for a big one

Earlier studies had said that chances of a major quake in Bhutan are minimal

Bhutan, for a while, had been resting easy due to some earlier studies that said that the likelihood of a major earthquake of magnitude 7 or 8 hitting Bhutan was minimal after the seismic active zone had shifted to about 180 km from the Himalayan foothills to the Shillong plateau, making Bhutan safer.

However, a seven-year long study on Bhutan’s geodynamics has come out with new findings that an earthquake of such magnitude could hit Bhutan, which is not as safe as it was earlier assumed.

The research started in 2011, two years after the damaging 2009 earthquake of magnitude 6.1 that hit Bhutan hard. The findings from the exploration of the region’s geophysics was revealed in October 2018.

The research team in collaboration with the Department of Geology and Mines, MoEA found that although seismicity rate in Bhutan has been low over the decades, they have, however, discovered evidence that at least one earthquake of a magnitude 8 had actually occurred in Bhutan in the past that was much stronger than any recent events- corroborating some earlier studies forewarning that an earthquake of such magnitude can occur again.

Earlier there were doubts about the likelihood of a similar event like the Nepal quake in 2015 happening to Bhutan. This was because though Bhutan had experienced several other earthquakes with a magnitude of about 6 during the past century, there was no clear evidence that Bhutan had ever seen an earthquake similar to the magnitude 7.8 Nepal event since the mega quake in 18th century (1714 AD).

Findings from recent geophysical exploration suggest that this confidence may be overly optimistic. These results have shown that the eastern Himalayas region is extremely complex compared with the rest of the mountain belt.

The team found that the region’s crustal structure, seismicity, and deformation pattern are all different from what scientists had speculated previously.

The team consisted of researchers from University of Lausanne, Institute of Earth Sciences, Switzerland, Géosciences Montpellier, Université de Montpellier, France, Department of Earth Sciences, Uppsala University, Sweden, Swiss Seismological Service, Zürich, Switzerland, Shejun Agency for Bhutan ‘s Cultural Documentation and Research, Bhutan, and Department of Geology and mines.

“The numerous low magnitude seismic events that Bhutan experienced so far are not capable of releasing the built-up stress that has been developing over the centuries. Even among the scientific communities, there is a clear understanding that an earthquake of magnitude 6 or 7 will not be able to release the stress accumulated over the years along the contact points of the shifting Asian and Indian sub-continental plates. There has to be an earthquake of magnitude 8 or higher in order to release the build-up stress, and no such earthquakes had hit the area in about many centuries in the region,” said Dr. Dowchu Drukpa, Chief Seismologist, Department of Geology and Mines, MoEA.

Dr. Dowchu said that in Bhutan the micro-seismic events seem to be more in the eastern parts of the country than in western Bhutan. “Although we cannot draw out concrete understanding of such occurrence, our GPS studies show that the western region seems to be locked which is why there are less micro-seismic events in the region. Whereas, in the eastern region, it apparently appears that the plates are active, which is why frequent micro seismic event takes place,” he said. However, he added that a detailed study needs to be carried out in the eastern region for better clarity on the nature of seismic waves in the region.

Should an earthquake of magnitude 8.5 or more hit the region, the chief seismologist said that none of the regions in the country will be safe, however, the northern parts of the country might be less vulnerable to massive damages as compared to the other regions.

“An earthquake of magnitude 8 or more will not only devastate Bhutan, but the entire region,” he said.

The chief seismologist said that there is no one who can predict earthquakes; however, he said that the experts can only forecast the susceptibility of the regions based on accurate geophysical characterization of each region.

“Scientifically, the department has been working hard in understanding the hazards and we have installed fourteen seismic source monitoring stations and twenty intensity meters in every dzongkhag,” said Dr. Dowchu Drukpa.

For more accuracy and proper monitoring, the Ministry has plans to install more intensity meters in all the 205 Gewogs in the country by next year. “Based on the shake maps generated post disaster, planning can be done accordingly when communication networks fails, which will help in the efficient rescue and evacuation processes- so it is very important. We are working towards developing a spontaneous display of shake map in the future,” said the chief seismologist.

The networks have been established with the financial assistance from World Bank under the supervision of Japan Policy for Human Resource Development project and also in collaboration with National Research Institute for Earth Science and Disaster Resilience, Kyoto University in Japan and Regional Integrated Early Warning System based in Bangkok.

Phuntsho Pelgay, Executive Geologist, Earthquake and Geophysics Division, Department of geology and mines said that some of the challenges faced by the division are to assess the machines for 24 hours due to shortage of man power and the erratic connectivity that affects their IT intensive servers.

Phuntsho Pelgay said that the division also plans to develop a Standard Operating Procedure and alert every cellular user in the country through SMS every time the intensity meters detect earthquakes as low as an earthquake of magnitude 2 in the country to create awareness among the public.

The Earthquake and Geophysical Division was formed only after the 2009 earthquake of magnitude 6.1, which collapsed buildings and traditional Bhutanese structures in the eastern Dzongkhags of Mongar and Trashigang and claimed 11 lives.

Since the infrastructures built before 1997 do not have the seismic design concept incorporated in building construction, Bhutan Standard Bureau (BSB) recommends retrofitting the building by modifying the existing structure to make them more resistant to seismic activity by adding the necessary components missed out during the initial construction.

BSB mandates public to follow the Bhutan building codes 2003 and ensure that the foundation is strong, weight is equal on all floors, there are thicker walls and pillars, strong lower floors and that beam rods are not joined in the middle or at corners.

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