Not possible to predict ‘big quake’: What geologists said

On Wednesday, NCS released a preliminary report of Tuesday night’s earthquake. The epicentre of the earthquake was in the Hindu Kush region, Afghanistan 988km NW of Delhi, and at a depth of 156km.

That the Himalayan region, including northern India, will see a big earthquake is something experts have known for many years — but they have always maintained that it will be impossible to predict whether this could come next week, or 30 years hence, or perhaps ever.

*People gather after a building tilts following an earthquake, at Shakarpur area in New Delhi. (PTI)

Indeed, whether Tuesday’s earthquake, the tremors of which were felt in India, Pakistan, large parts of Central Asia including Uzbekistan, Tajikistan, Kazakhstan, Kyrgyzstan and Turkmenistan was the big, once in a 100-year earthquake expected in the Himalayan region, or a precursor of one, is not only impossible to say but also unethical to speculate on, geologists said on Wednesday.

They also have a simple piece of advice for people: Don’t panic.

“One argument will be that there are multiple powerful earthquakes in the region so the place is releasing energy slowly and hence hereafter a large earthquake is not expected. Another group can argue that the region is releasing energy gradually and hence we can expect a more powerful earthquake in future. Who can tell? So, these are absolutely vague things and we should not panic over these issues,” said M Ravichandran, secretary, ministry of earth sciences.

Data from the National Center for Seismology shows that there have been at least three earthquakes of a magnitude of 6.6 (the magnitude of the earthquake in Afghanistan) or higher since 2013 in the Himalayan region (HT analysed data for the rectangular region covering 26-37 degree North and 72-90 degree East from the National Center for Seismology. This is a rectangle , with one pair of sides parallel to the equator, that runs roughly from Ladakh in the north to Assam in the east. It also covers Nepal and parts of China).

There have also been seven earthquakes in the region of magnitude 6 or higher, and 76 of magnitude 5 or higher. The three earthquakes of the highest magnitude (7.9, 7.3, and 6.6) were all located in Nepal and took place on April 25, May 12, and April 26 in 2015.

Many of these 76 earthquakes were shallower earthquakes than the 156km -deep earthquake that struck Afghanistan. 54 of the 76 were of depth up to 10km , nine were 10-20km deep, eight were 20-50km deep, two were 50-100km deep, and three were 100-150km deep. These deepest three earthquakes were of magnitude 5.2 or 5.3 and located just at the tip of India’s northern boundary and north-western edges of Ladakh. They took place on October 21 in 2013, July 8 in 2014, and December 7 in 2017.

The focus of governments, Ravichandran added, should be on preventing damage. “Japan is doing that. They are extremely vulnerable but the focus is on building resilient infrastructure. The building codes and guidelines for earthquake resilience will have to be followed in the Himalayas. We have very high population density both along the coasts which are facing sea-level rise and in the Himalayan regions.” According to him, it is possible to limit damage by ensuring that these codes and guidelines are implemented.

And it makes no sense to try and predict when the big one will come, simply because it’s not possible to.

“Forecasting of earthquakes is not possible in space, time and magnitude. Almost entire Himalayas and Hindu Kush Himalayan region is in seismic zone 5 and earthquakes can happen anytime there. In zone 5 a big earth quake is possible . High seismic zone areas can record power earthquakes but nobody can tell when or how powerful,” said JL Gautam, head of office and Scientist at the National Centre for Seismology.

On Wednesday, NCS released a preliminary report of Tuesday night’s earthquake. The epicentre of the earthquake was in the Hindu Kush region, Afghanistan 988km NW of Delhi, and at a depth of 156km. The area is seismically very active associated with collisional tectonics where Indian plate subducts beneath the Eurasian Plate.

“The event was well recorded by more than 100 broadband seismic stations installed by National Centre for Seismology. The analysis of seismic data shows that the event was occurred near the Herat Fault. The preliminary fault plane solution derived from moment tensor inversion suggests that the earthquake is associated with thrust fault mechanism,” the report said.

The earthquake was widely felt in Delhi-NCR region and neighbouring states. More than 70 “felt reports” due to this earthquake received from Jammu & Kashmir, Delhi, Uttarakhand, Uttar Pradesh, Himachal Pradesh, Rajasthan, Haryana, Punjab, and Gujarat have been registered with NCS.

“The reason it was felt up to a great distance is because of its high depth of over 150km, so first the primary waves and then secondary waves were also felt up to a large distance. But even if the depth is shallow but magnitude is high such an earthquake can also cause massive localised damage. In fact, if the depth is more the damage may be relatively low but the tremors will be felt up to a greater distance,” Gautam added.

The Himalayan region is seismically one of the most active continental regions. It experienced at least four magnitude 8 earthquakes during an active phase from 1897 to 1952 according to a paper titled “Himalayan Earthquakes and Developing an Earthquake Resilient Society” published in Journal of Geological Society of India in 2020.

Detailed investigations have revealed that the region is currently in a seismic quiescence phase, and enough strains have been accumulated, but that still does not make it easier to predict when and where the next big one will be.