CHENNAI: Mild tremors were felt in parts of Chennai as an earthquake measuring 5.1 magnitude on the Richter scale hit the Bay of Bengal region on Tuesday afternoon.
The quake, reported at 12.35 pm, was at a depth of 10 km in the Bay of Bengal and was about 296 km south-south east of Kakinada, Andhra Pradesh and 320 km east north east of Chennai, confirmed officials at the National Centre for Seismology. Meanwhile, the Indian Tsunami Early Warning Centre ruled out any tsunami threat.
A seismologist from the National Centre for Seismology told The New Indian Express that the location where the earthquake occurred is close to the mid-oceanic ridge. "There are two ridges which are located 85 degrees east and 90 degrees east. This earthquake has occurred close to one of these ridges. These are actually aseismic ridges, which means they are not supposed to produce earthquakes. But since these are topographically high, they are slightly active and can once in a while trigger earthquakes. In February 2019 also, an earthquake of similar magnitude was reported in the Bay of Bengal region," he explained and added that the Bay of Bengal region on the Indian tectonic plate was not prone to earthquakes.
This Indian plate ranges from the Himalayas to Africa to Andaman to 1,000 km off the Chennai coast. "It is a very stable tectonic plate," the official said. However, seismologists from Indian Institute of Sciences, Bengaluru, say it is a major concern that a quake has struck so close to the east coast of India. The last earthquake in February 2019 was reported about 447.4 km northwest of Visakhapatnam and 609.1 km west-southwest of Chennai. Now, this quake was reported just over 300 km off the Chennai coast.
Brushing aside fears, D Srinagesh, Head of the Seismology Observatory in the National Geophysical Research Institute, told The New Indian Express that there is nothing unusual about these moderate earthquakes in the Bay of Bengal region. "But, we have to keep a close watch on the underwater ridges and fault lines in the region along the east coast. Occasionally, they get seismically active when stress builds up."
He said except for one 5.1 magnitude earthquake, there were no aftershock events reported on Tuesday. The seismic stations in Chennai, Kalahasti or Warangal did not record anything. "People have only reported mild tremors for about one to two seconds," he said.
TM Balakrishnan Nair, director of Operational Ocean Services and Applied Research (OSAR) Group at the Indian National Centre for Ocean Information Services (INCOIS), told The New Indian Express that there was no perceived threat. "The early warning centre at INCOIS continuously monitors seismic and sea-level data. We should be concerned only when an earthquake in excess of 6.5 magnitude strikes."
The early warning centre at INCOIS detects all earthquake events of more than 6 magnitude occurring in the Indian Ocean in less than 12 minutes. Bottom Pressure Records (BPRs) installed in the Deep Ocean are the key sensors to confirm the triggering of a tsunami. The centre uses a custom-built software application that generates alarms/alerts whenever a pre-set threshold is crossed. Tsunami warnings/watches are then generated based on pre-set decision support rules and disseminated to the concerned authorities for action, following a Standard Operating Procedure.
When contacted, Director of State Disaster Management N Subbaiyan said some parts of Tamil Nadu, including Chennai, have only reported mild tremors. "There is no threat of tsunami or storm surge. No warnings at this juncture are warranted."
On Tuesday, many Chennaites took to social media to report the tremors. People living in areas like Adyar and neighbouring Thiruvanmiyur said they felt mild tremors, with some Twitter users saying they could even see the furniture 'shaking.'