Barak Valley is in a high risk earthquake prone zone

Silchar, March 3: The tremor of Saturday that hit Barak Valley and the adjoining Sylhet district of Bangladesh which was of magnitude 5.5 on Richter Scale has again brought to the fore the relevant question:: is this zone prone to earthquake? The jolt felt by the people in the early morning was so severe that it created a sense of panic among the people. The tremor was followed by aftershocks. Fortunately, the tremor that originated in the south west of Karimganj caused no damage or loss of life.
In the wake of the Cachar tremor in 1984 on March 31 which hit Sonai block, killing 8 persons in the area, a team of experts from Regional Research Laboratory, Jorhat, and ONGC geologists from Nazira and Dehradun carried out investigations to find out the causes of earthquake, pinpoint its epicentre and all other structural causes.
According to their findings, Cachar tremor of 1984 was the result of the bending of a block of earth's crust by stresses operating horizontally which reduced its elastic limit and suddenly yielded to fracture, displacement or faulting. The sudden shifting furnished the impulse which sent out vibrations into surrounding areas of the earth, causing the tremor.
Their observation is that earthquakes generally occur in regions of marked instability of the earth's crust, such as geologically young mountains. Such a region is the zone of the Himalayas. It is therefore not surprising that Barak Valley along with entire Assam is an extended part of the Himalayas and therefore frequently shaken by earthquakes. Between August, 2009 and March, 2013, this valley has been rocked by quakes 7 times.
The Himalayas are still going on expanding and this 'continental drift' accounts for the drifting of the entire landmass of the north east region from 4 to 5 cm every year. This makes the region, the finding said, seismically active. The National Geographical Research Institute of Hyderabad, in course of their studies, identified two earthquake zones or seismic belts in the world. These are Trans Atlantic and Circum Pacific which unite at the corner of Indo–Myanmar, making it most unstable region in the world.
The first movement of a major earthquake is followed usually for days or months by a succession of aftershocks. In the second Assam quake of 1819, the aftershocks continued for a period of 10 years. The Assam quake of June 12, 1897 is perhaps one of the most severe ones in the world to occur.
Though earthquakes are unpredictable in general, it is interesting to note that during the tremor of 1984, the villagers of Sonai in Cachar had in particular noticed unusual behavior among bats, birds and squirrels before their area was hit by the quake. Geologists of ONGC in course of their investigations in the area discovered that the earth developed many linear cracks, squeezing out deep grey coloured sand with some clay and hot water.
The eruptions through cracks were in the form of geysers of strong yellowish tinge along with specks in rainbow colours, discovered in water, which is believed to contain some ferruginous contents. Their studies have also revealed that a seismic belt termed as 'Haflong Thrust' runs through the Borail and North Cachar Hills. As Barak Valley is part of the Arakan basin, tectonic movement results in folding or faulting of the zone which makes it quite susceptible to earthquake.
Dr Somnath Dasgupta, Vice–Chancellor of Assam University and an eminent geologist with his research work on earthquake, while identifying the origin of the quake of last Saturday 26 km away from the south–west of Karimganj, describes Barak Valley as being located in the fifth seismic zone of the country and is highly risky. Though the tremor was measured at 5.5 on Richter Scale, the impact was felt severely as the vibrations or waves were down 40 to 47 km inside the earth. He identified 'Sylhet–Fault' as a contributing factor to the tremor. (Source:SentinelAssam)