Kolkata lies right on top of faultline, may face major quake in future

  • Joydeep Thakur, Hindustan Times, Kolkata
  • Updated: May 14, 2015 01:40 IST

Every time the ground shakes beneath Kolkata, we move an inch closer to Dooms Day, experts warned after Tuesday’s earthquake in Nepal.

For there lies a ‘faultline’, a fractured zone, just 4.5km below the city, which has been lying almost in active for years but could become hyperactive and trigger a massive quake measuring at least 6 on the Richter scale, seismologists claim.

“This could turn the 300-year-old city in torubble within minutes. It’s just a matter of time,” said Supriya Mondol, associate professor with Jadavpur University who deals with plate tectonics and quakes.

The fracture, known as the Eocene Hinge Zone, runs right through the middle of the city and then cuts across Rajarhat-Newtown and Ranaghat, in Nadia, before passing through Bangladesh and Myanmar and, further on, to Sumatra.

Experts say this faultline is lying almost inactive. Since it is not located on the edge of any tectonic plate, such as Nepal, the areas along this fault, including Kolkata, have not experienced any major earthquake in recent times. Minor earthquakes, which humans can hardly feel, however, do take place.

“But the Indian plate, which contains the faultline, is continuously pushing northwards and sliding beneath the Eurasian plate at a rate of 40mm each year. This is what resulted in the Nepal earthquake. The Indian plate is also pushing against the Burma plate, which triggered the 2004 tsunami,” said Sankar Kumar Nath, an IIT-Kharagpur professor who has been teaching seismology over the past 27 years and has also received the Shanti Swarup Bhatnagar Prize. Because of the stress and strain, the energy which is getting accumulated along the faultline will try to release itself through the ‘fracture’. This might trigger the earthquake.

Since April 25, when an earthquake measuring 7.9 on the Richter scale hit Nepal killing thousands, there have been more than 100 aftershocks. On Tuesday, there was another quake measuring 7.3 on the Richter scale followed by at least six aftershocks within just two hours.

“This continuous stress and strain - the Indian plate rubbing against two others - could turn the faultline below Kolkata into a hyperactive zone and trigger a massive earthquake in future.

The energy thus liberated will be so huge that it’ll trigger an earthquake measuring not less than 6 on the Richter scale. I leave it to you to guess what the results will be,” Nath said.

Is an earthquake measuring 6 on the Richter scale strong enough to turn Kolkata into rubble? The answer came from different quarters. Both the quakes that hit Nepal on April 25 and on Tuesday measured more than 7 on the Richter scale at the epicentre, but the tremors felt in Kolkata and its surrounding areas were just 4-5 on the scale. Yet, they were strong enough to shake buildings.

“Now, imagine a quake measuring 6 with the epicentre just beneath Kolkata,” a senior officer of the Indian Meteorological Department’s regional office in Kolkata said.

A former senior director of the Geological Survey of India said, “The city had a close shave on both April 25 and Tuesday. The tremors felt in the city were not more than 5 on the scale. Kolkata won’t be able to withstand an earthquake beyond 6. A quake measuring 6 would kill a few lakhs and bring down several old and quite a few new multi-storeyed buildings.”

Scientists, however, failed to answer the biggest question of all: When?

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