By Madhuparna Das
Kolkata, May 14 : Since September 2-11, when an earthquake of magnitude 6.9 rocked Sikkim, scientists have recorded nearly 300 aftershocks in the region and predicted the possibility of a quake up to magnitude 9. As such, they have recommended that parts of Sikkim be upgraded to Zone 5, the classification that carries the highest risk.
The seven Northeast states are in Zone 5 — Assam and Meghalaya had a magnitude 5.4 earthquake last week. Sikkim is now in Zone 4. The prediction — by researchers of the department of geology and geophysics of IIT Kharagpur— is for a northeastern region that includes the Sikkim-Darjeeling region in particular.
“The entire northeastern zone is at present facing the threat of an earthquake from the Himalayan regions, one that has the potential of being of magnitude 9,” says Professor Shankar Nath of IIT Kharagpur.
Scientists studying aftershocks recorded 292 tremors since the Sikkim earthquake, all in the range 1.5 to 5 and including 63 in the range 3.5-5, with 17 of these of magnitude 4.5 or higher. “We have completed part of our Sikkim-Darjeeling project. We have recommended that parts of Sikkim including Gangtok, Mangan and Singtham be updated to Zone 5 from Zone 4,” Professor Nath says.
Scientists have also sought an upgrade for parts of the Doors and Terai regions of West Bengal.
Months of study have resolved another contentious issue over which the scientists had been divided. Geo-scientists have come to agree that the earthquakes frequently hitting Sikkim and neighbouring areas of Bengal have not been induced by water reservoirs.
“After the September 18 earthquake, there was a brainstorming session... we reached a conclusion that the earthquake is not reservoir-induced; therefore hydel projects are not a threat to the area.” Geo-scientists are of the opinion that the earthquakes have originated rather from tectonic shifts.
Sikkim government officials say the state has 27 hydel power projects, of which four are operational. According to professor Nath, “The projects can be affected due to earthquakes, but the projects cannot cause earthquakes.”
Professor Sugata Hazra, a senior professor of geology and head of the school of oceanographic studies of Jadavpur University said, “The seismicity in these regions has increased and these are not reservoir-induced earthquakes.
So we think that the Sikkim and Bengal governments have to revise disaster management plans. If a strain is building up then the region can potentially have an earthquake of magnitude 8.5 in the near future.”