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Himalaya poised to rupture in mega earthquakes

American geophysicist investigates data worth thousand years to outline earthquake potential of Himalayan segments more precisely.

K. S. Jayaraman

doi:10.1038/nindia.2019.25 Published online 24 February 2019

Experts say outreach programmes should be undertaken to appraise people living in remote Himalayan villages about the impending threat.

© S. Priyadarshini

The chorus of voices pointing to an impending mega earthquake in the Himalayan region got louder this month when leading American geophysicist Roger Bilham cautioned in a new analysis that "currently two-thirds of the Himalaya is poised to rupture in one or more great earthquakes.”

“…although we have no information of their timing,” he adds in a 60-page review1 of the Himalayan earthquakes published in a special collection of the Geological Society of London.

The University of Colorado geophysicist says the most alarming feature of potential future earthquakes in Himalayas is that none is expected to be smaller than the 7.8 Mw magnitude Gorkha earthquake of April 2015 that killed over 10, 000 people. His prediction is based on extensive field studies and examination of 1000 years of historical, geodetic and seismological data of the Himalayan arc.

According to his report, "ten of the 15 segments of the Himalayan arc have not ruptured so far and are currently sufficiently mature enough to host a great earthquake of magnitude 8 Mw or more".

This does not imply it will cause "unprecedented violent shaking but the duration of shaking may exceed many minutes," he says. "This prolonged shaking is likely to aggravate damage to poorly constructed structures."

Bilham estimates that the death toll from a future earthquake in the Himalaya "could possibly exceed 100,000 due to increased population and the vulnerability of present-day construction methods.”

The 2015 Gorkha Earthquake of magnitude 7.8 Mw killed more than 10, 000 people and caused massive damage in Nepal.

© Chhatra Karki

Considered an authority on earthquakes in the region, Bilham has been invited to a brainstorming session on the "Big One", an allusion to the mega earthquake being predicted in the region, at the Indian Institute of Technology (IIT) Mandi in April 2019. He will participate in an international workshop on climate change and extreme events in the Himalayan region.

According to Vineet Gahalaut, director of National Centre of Seismology in New Delhi, Bilham's in-depth analysis of available information on earthquakes in the Himalayan region provides results from paleoseismological investigations. “He has elaborated on several aspects of Himalayan earthquakes including the earthquake potential of different Himalayan segments, which he has been updating since 2001,” Gahlaut told Nature India.

Recent earthquakes with epicentres in Afghanistan and surrounding regions have affected Delhi and the national capital region of India, says Ramesh Singh, a former President of the American Geophysical Union Natural Hazards Group. "Depending on the Himalayan segment, people living in Delhi and surrounding regions may severely feel the earthquakes and suffer damages”, Singh, currently a professor at Chapman University in California and also the convener of the IIT Mandi workshop, says.

Singh says this may be the right time for people living in the Himalayas and surrounding regions to review existing buildings and structures and prepare for exigencies. "We must also begin outreach programmes to tell people living in remote places in the Himalaya about the (impending) Big One."


References

1. Bilham, R. Himalayan earthquakes: a review of historical seismicity and early 21st century slip potential. Geological Society, London, Special Publications, 483 (2019) doi: https://doi.org/10.1144/SP483.16