Mild tremors shook parts of Kolkata around 5.15am on Friday.
The tremors lasted a few seconds and no casualty was reported.
An earthquake with its epicentre in Myanmar, which measured 6.1 on the Richter scale, had triggered the tremors which were also felt across Tripura, Manipur, Mizoram and Assam, besides Bangladesh.
The earthquake had its epicentre 12km inside the earth’s crust from 73km southeast of Thenzawl in Mizoram, according to the National Centre for Seismology. The distance from Kolkata would be over 1,600km.
In seismic parlance, a quake of magnitude 5 just about qualifies as “strong”.
The Richter scale stays constant in all places a quake is felt, but the damage potential varies depending on the distance from the epicentre.
The Nepal quake in April 2015 that killed many measured 7.8 and was classified as “major”. The epicentre had been over 900km away but the tremors had been felt in Kolkata.
“Had the epicentre been closer to the surface, the waves could have been stronger,” said Sankar Kumar Nath, professor of geophysics at IIT Kharagpur.
Many Kolkatans were asleep when the tremors happened. But many of those who were awake, or jolted out of their beds by the tremors, scurried down to the streets for safety.
Many offices in Sector V and Rajarhat and New Town, where people work in night shifts, became empty.
New Town resident Ranjan Basu, who stays in a 12th-floor apartment at the Rosedale Housing Complex, said that he felt the entire apartment shudder for several seconds as he was getting ready to step out for his morning walk.
“I had just placed the cup of tea on the saucer in the drawing room when I felt the whole building shake and shudder. I immediately looked out of the building and was about to ask my wife to get out when the tremors stopped,” Basu said.
“Several residents felt the tremors. There was a lot of buzz in our WhatsApp group,” said Deepak Agarwal, president of the residents’ association of Diamond City West housing complex in Behala.
Social media was also flooded. “Earthquake in Kolkata! Wow, twitter is reassuring. No one in home believed me when I ran to them scared,” Arpita Goon tweeted at 5.32am.
“Thought I was having some kinda dizziness. Then sankher shobdo (sound of conch shells) along with mom calling,” said a tweet from a handle named @mimpful.
Geologists believe Kolkata’s vulnerability to a major quake epicentred nearby is high because of its alluvial or unconsolidated soil, the kind in which earthquakes tend to cause extensive damage.