The Great Himalayan Earthquake: A matter of 'when' not 'if'

More than 1,000 people have died, and nearly 2,400 others were injured after a powerful earthquake of the 7.7 magnitude struck Myanmar and also neighbouring Thailand on Friday. Myanmar is vulnerable to earthquakes because it sits on a geological fault line. Located along one of the world's most active seismic belts, Myanmar has many fault lines and shifting tectonic plates.

Meanwhile, a 4.3-magnitude aftershock rattled the region on Saturday, further complicating rescue and recovery operations.

In India, the Himalayas are most prone to earthquakes. Experts have highlighted the possibility of a 'Great Himalayan Earthquake'. Any major seismic activity in the region always brings to fore this vulnerability. The impact of such a large earthquake of magnitude of 8 or above can also impact the National Capital Region of Delhi.

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A matter of 'when' not 'if'
American geophysicist Roger Bilham has warned that the Himalayas are the only place in the world where a large quake can occur on land. "India slides 2m beneath the southern edge of Tibet every century. Unfortunately, its northern edge does not slide smoothly but is hung-up (by friction) for hundreds of years and catches up in minutes when this friction is overcome. The slip events, which we call earthquakes, are the inevitable and unavoidable consequence of this motion," Bilham had told TOI in an interview in 2020.

Bilham has explained why the Great Himalayan Earthquake is inevitable even though experts can't say exactly when it can happen.

"Great earthquakes with magnitudes exceeding 8 on the Richter scale have been occurring in the Himalayas every few hundred years. We have geological evidence that earthquakes as large as M=8.7 have occurred many times in the past 2,000 years. However, no magnitude 8 earthquakes have occurred in the past 70 years to release the pressure in the Himalayan arc. Two or more regions of the Himalayas must soon rupture in a great earthquake. It is not a matter of “possibly”. They must occur. Unfortunately, scientists are unable to offer any insight into their precise timing," Bilham had told TOI.

Also Read: Myanmar earthquake kills over 1,000, leaves 2,376 injured in widespread devastation

"India’s emergency management services are aware of the earthquake risk. They are also aware of the uncertainty in the timing of a future great Himalayan earthquake, which could occur tomorrow, or in 10 years, or not for a hundred years. A future great Himalayan earthquake (with magnitude between 8.2 and 8.9) will, however, be unprecedented because the Himalayas are the only place in the world where such a large earthquake can occur on land, exposing about 300 million people to prolonged violent shaking. Usually the violence of these great earthquakes is largely directed offshore. Because of its land-based setting, northern India is uniquely vulnerable to rare great earthquakes. India’s written history does not record what happened in previous mega-quakes, when populations were lower and when building styles were better suited to strong, prolonged shaking," he said.

As per a study which appeared in the journal 'Seismological Research Letters' in 2020, the entire Himalayan arc is poised to produce a sequence of great earthquakes, and the next big quake — of the magnitude of 8 or above — may occur during our lifetimes. The human toll of such an event in the densely populated countries across the arc is likely to be unprecedented, the researchers said.

"These earthquakes will occur again and scientifically, it would not be a surprise if the next great earthquake occurred in our lifetimes. But the resolution of our studies is at best on the order of 100 years, longer than a human lifetime," study author Steven G. Wesnousky, a professor of geology and seismology and director of the Center for Neotectonic Studies at the University of Nevada at Reno, US, had told PTI.

Seismologist Supriyo Mitra had noted that the research matched previous studies. "The Himalayan faults, as shown in the paper, are poised to produce an 8-plus magnitude earthquake. So yes, we are staring at a big one in the future. How far from now no one can tell," Mitra, who was not involved in the study, had told PTI.

Major cities along and close to the Himalayan frontal thrust include Chandigarh and Dehradun in India; and Kathmandu, Nepal. Strong and damaging shaking in such great quakes could extend southward as far as India's capital, Delhi.

A top expert, Vineet Kumar Gahalaut, had said at an event in 2017 that there is a large amount of strain accumulation in the Kumaon-Garhwal Himalayas. “Considering that no great earthquake has occurred in the past 500 years or more, this region has high potential for occurrence of a great earthquake,” he said.

Growing population a risk
Earthquakes are inevitable in almost the entire cross-section of the Himalayas and adjoining plains and a population of more than 50 million is at risk, as per a research that studied the hazard in the aftermath of the 2001 Bhuj temblor. The study, Himalayan Seismic Hazard, published in Science magazine in 2001, said the longer the time interval between the last big earthquake in the region and the next major one, the higher the possibility of future quake unleashing more devastation.

The exploding population in the region greatly increases the risk of casualties. The research compared the 1819 Kutch quake with the 2001 Bhuj temblor to illustrate the dangers. “The population of Kachchh has increased by a factor of 10. Around 2,000 fatalities occurred in 1819, compared to the 18,000 confirmed and possibly 30,000 unconfirmed fatalities (in Bhuj). The implemented seismic code apparently did not lessen the percentage of the population killed,” it said.

“Projecting these figures to just one of the possibly several overdue Himalayan earthquakes (for example a repeat of the Kangra 1905 event) yields 2,00,000 predictable fatalities. Such an estimate may be too low by an order of magnitude should a great earthquake occur near one of the megacities in the Ganges plain,” the research paper said.

(With inputs from TOI and agencies)