Why Barak Valley prone to quake?
SILCHAR, Jan 5: Barak Valley along with the entire Northeast has been hit by a severe earthquake on Monday, causing serious concern among the people of this region. The latest report from the three districts of Cachar, Karimganj and Hailakandi indicates around 63 persons have been injured, some of them seriously, necessitating their admission in PHC or civil hospital or Silchar Medical College Hospital. Several buildings have also been badly damaged, assessment about which is on the way by the competent authority. Some of the apartments in this town have shown cracks, mostly on the ground floor, and the residents are in search of altertive accommodation.
In recent memory, the earthquake of January 4 this year has brought to the memory of elderly persons the tremor of 1950 which had rocked this valley, claiming life and properties. In fact, this valley has been rocked by tremors several times. One would recall that in 2009, this region was hit by quakes for four times in 23 days. This cannot but evoke the relevant question: how safe is our zone? The tremors of 2009 with their origin along the Indo-Myanmar border did not cross the danger mark of 5.6 on Richter scale, causing no damage or loss of life.
But, January 4 jolt with its epicentre at Tamenglong in Manipur reached the Richter scale of 6.7. According to seismologists, any quake that touches 7 on Richter scale is severe in dimension. It would be relevant to refer to the Cachar tremor of March 31, 1984, which hit Soi block. A team of experts from Regiol Research Laboratory of Jorhat and ONGC geologists from zira and Dehradun carried on their studies and investigations in order to find out the causes of earthquake, locate its epicentre and all other structural causes. 10 people died during the 1984 tremor.
According to their investigation, the 1984 Cachar tremor was the result of bending of a block of earth crust by stresses operating horizontally which reduced its elastic and plastic limit and suddenly yielded to fracture, displacement or faulting. The sudden shifting furnished the impulse which sent out vibrations or waves into surrounding areas of the earth, leading to 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 and entire Assam which are an extended part of the Himalayas and are about 20 million years among the youngest mountains of the world are frequently shaken by earthquakes.
The Himalayas are still growing and expanding and this continental drift accounts for the drifting of entire land mass of the northeast region from four to five cm every year. This makes the region, the findings say, seismically active. tiol Geophysical Research Institute of Hyderabad identifies two earthquake zones or seismic belts in the world- Trans Atlantic and Circum Pacific which unites at the corner of Indo-Myanmar border, making it the most unstable region in the world.
The first movement of a major earthquake is usually followed for days and even months by a succession of aftershocks. In the second Assam quake of 1819, the aftershocks continued for a period of over 10 years. The 1897 Assam quake on June 12 is perhaps one of the most severe to occur in the world. Though earthquakes in general are unpredictable, it is interesting to note that during the tremor of 1984, the villagers of Soi in Cachar had in particular noticed unusual behaviour among bats and squirrels before their area was hit by the tremor.
Geologists of ONGC in course of their investigations of the area discovered that the earth developed many linear cracks, squeezing out deep and grey coloured sand with some clay and hot water. The eruptions through cracks were in the form of geysers. Strong yellowish tinge along with specks in rainbow colour discovered in water 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.
‘Haflong Thrust’ forms part of the land set image of aerial survey of the ONGC. Apart from that as Somth Dasgupta, former Vice-Chancellor of Assam University and an eminent geologist, in the wake of the Nepal earthquake which jolted this valley also, though mildly, identified yet another seismic belt which he termed as ‘Sylhet fault’. 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 tremor.