BHUBANESWAR: Even as geo-scientists debate if the 7.9 magnitude earthquake that devastated Nepal on Saturday was the ‘big’ seismic event expected in the Himalayan region where the Eurasian tectonic plate is constantly being pushed by the Indian plate, a coastal State like Odisha needs to watch out for the intra-plate faultlines and remain prepared.
While the State felt the tremors of Nepal earthquake, what it must be wary of is the faultline in Bay of Bengal which makes the Mahanadi valley a vulnerable zone. Though most parts of Odisha are classified as Earthquake Risk Zone-II (low damage risk), the Brahmani-Mahanadi graben and its deltaic areas come under moderate damage risk zone or Earthquake Risk Zone-III.
Over 40 urban local bodies including Bhubaneswar, Cuttack, Paradip, Dhenkanal, Angul, Sambalpur and Deogarh, which are home to major industrial installations, fall in Zone III. What’s significant is that the earthquake of magnitude 6 on the Richter scale which shook Odisha last year on May 21 originated from Bay of Bengal, about 310 km from Bhubaneswar.
DK Rai, Deputy Director General (Geology) of Geological Survey of India (GSI), Odisha Unit says the intra-plate faultlines are activated when the pressure is high along the boundaries of tectonic plates.
“If you look at Earthquake Risk Zone-III in Odisha, it passes parallel to river Mahanadi where all the coal deposits lay. Besides, alluvial soil makes the region all the more vulnerable. It is a moderate damage risk zone but preparedness and precautions are necessary,” said Rai, who worked extensively on the Bhuj earthquake in 2001.
While the Indian tectonic plate is moving about five centimetres a year, getting under the Eurasian plate leading to collision, it leaves all intra-plate faultlines or lineaments active. Rai said the faultlines’ location is as important as their length. “What is significant is none can predict when the faultlines can release the energy caused by the interaction between plates,” he said.
After last year’s earthquake in Bay of Bengal, four experts from GSI also published an article in International Journal of Research in Engineering to get a geophysical insight into the seismic event through study of magnetic field. It found existence of major faultlines along North West-South East and North East-South West directions in the study.
The report concluded that the stress release activities from these lineaments may be responsible for the seismic event. The movements along the growth faults due to huge sediment loads could also play a significant role. “Such moderate earthquakes are likely to occur in future but the probability of destruction due to earthquake is less. Disaster monitoring and management agencies with the coordination with scientific organisation should be prepared for these inevitable events,” the report said.