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Exclusive interview with Prof Devesh Walia only on Sentinel Assam

Of late, the Northeastern states, particularly Mizoram, Assam, Meghalaya, Manipur have been experiencing several tremors.

Devesh Walia

Sentinel Digital DeskBy : Sentinel Digital Desk

  |  21 Aug 2020 2:44 AM GMT

Of late, the Northeastern states, particularly Mizoram, Assam, Meghalaya, Manipur have been experiencing several tremors. We caught up with Prof Devesh Walia, Department of Environmental Studies, NEHU, Shillong to know more about why these quakes are happening and if the region would soon face a major quake.

Here are excerpts from the interview.

Sentinel Assam: Why is Mizoram and other states of Northeast experiencing so many tremors?

Prof Devesh Walia: The Indian plate over the past 71 million years has moved almost 1,000 kilometers from the southern hemisphere to the northern hemisphere, after that it has collided with the Eurasian plate. The convergence is going on and second important thing is that this convergence is towards the Himalayan region. After the collision with the Eurasian plate, the Indian plate has moved in anti-clockwise direction and it is colliding with the Myanmar plate also, so in the northeastern part of India, there are two convergences -- one is towards the North with the rise of the Himalayas conduction convergence and the other one is with Burmese state or Myanmar plate. This syntax zone becomes very important specially with respect to the tectonics which has got potential to give rise to the earthquake in this reason.

Sentinel Assam: Even the National Capital Region had experienced a lot of tremors.

Prof Devesh Walia: The Indian plate is moving and with this convergence is going on, which is giving rise to lot many earthquakes. And if I compress them in the direction of the compression and perpendicular to the direction of the compression there is extinction is there. So, either direction of compression or direction of extension these earthquakes they have been occurring. Now if you link it with the lockdown, one important thing definitely less noise is there because of the less movement of the vehicles so we are able to pick up, we are able to segregate even the lesser magnitude earthquakes and there is nothing to panic about it, normally such tremors keep occurring but we should be concerned of 4 plus magnitude because they have got the potential to destabilize any region and more amount of energy is released. With every magnitude increase, there is 30 times more release of energy. We have to do some systematic research to find out more about these earthquakes.

Sentinel Assam: You have been doing a lot of research, so what are the indications? Are we actually looking at a bigger tremor any time soon?

Prof Devesh Walia: We are have carried out deeper crystal configuration survey means from the surface of the Earth up to around 60 kilometers deep , we have found all those structures which are seismogenic in nature means they have got the potential to generate the seismicity in any area, especially the northeastern part, we have carried out not many such surveys as our instrument are still in Aizawl and in Meghalaya to record the seismicity in the region, especially this part of India is seismically very active. If you record the seismicity in Meghalaya and we record for three months 90 earthquakes in this region has been occurring and they keep on occurring. This is one of the six most seismically active regions of the world, after Mexico, Japan. That's why on the basis of the intensity and on the basis of the past events which have occurred in this region whole of Northeastern region falls in Zone 5 of the earthquake zones. Many people think that if these earthquakes they occur in this zone, then it is giving out energy and as the energy is released probably there will not be any major earthquake.

You can see that in the past 14-15 days so many earthquakes have occurred, now the thing is specially in Mizoram when we carried out the work we noticed the compression as I said with Myanmar plate, this Myanmar plate zone of compression is there which is also known as Zone of Convergence or Zone of subduction because when two plates they collide then one of the plate goes down beneath the other plate as this plate it goes down it rubs and because of this rubbing it gives rise to earthquakes and that's what is the subduction zone. These earthquakes are occurring at a depth of 10 kilometers only, so we need to be little cautious of these earthquakes.

If these earthquakes they are putting pressure and the pressure makes the rocks to break, this is what is a zone or stage core of a latency, if it is ready to break if more pressure will be there, it will break then it may give rise to some major earthquake and bring disaster. The movements are happening very close to Aizwal town. We have proposed to the government of Mizoram to place some seismometers along the Zone where the cases are occurring so that precisely because of what reason they are occurring can be studied and once we know then only we can think of further proposing some counter-measures and even telling the people those who are residing within that area to take some measures so that at least they are able to save their life if not property.

Sentinel Assam: What about the rest of North East because Assam, Meghalaya, Manipur also has been experiencing quite a few tremors.

Prof Devesh Walia: The major earthquakes have potential to destabilise any region, in 1897 there was one major earthquake at Meghalaya-Assam border and there was one major earthquake on 15th August 1950 in Upper Assam when River Brahmaputra changed course and ate away some parts of Dibrugarh town. Although in 1908 and 1934 there were two more earthquakes. Most of the northeast is vulnerable, but presently these earthquakes are restricted in certain zone, say from last June 22nd onwards they are occurring in those areas which are less vulnerable, less populated. But still the danger is there for whole of the Northeast but once it occurs at 10 kilometers depth, it comes to the surface to the epicenter then only from there, it starts moving the destructive surface waves, they start building, they start moving destabilising the buildings. So the important thing is that although Northeastern as a whole is high-risk area, presently we need to worry more about the Zone where the earthquakes are occurring.

We need to know if the present-day earthquakes are related to the tectonic convergence of these plate or they are due to release of some of the stresses which are stored in a compressed layer and they are getting released. If they are only releasing, its good but this should not be due to the whole movement of the plate because if Indian plate is moving and putting the pressure, it has got huge potential to destabilise the region. That's what we are trying to study. We have got some of the global positioning systems installed even in Meghalaya and in Aizawl so that we know with what speed all the plates are moving and whether the energy is getting stopped and could give rise to major earthquakes.

Government of India have placed some multi-parametric geophysical observatories, one is in Manipur which is maintained by Manipur University, second one is at Tezpur which is maintained by Jorhat and one is at Shillong which is maintained by Indian Institute of Geomagnetism. They measure around 13 parameters, but still it is not so easy to forecast or to predict earthquakes. But only thing is we can demarcate the Zone where say if the plate is moving so there is in general seismicity or energy is getting released so it is not getting stored. If the P-value is less than one it means some energy is getting stored and in all these areas it is less than one so energy is getting stored in some of the blocks if we know those blocks at least we can tell the people residing in those areas to take precaution because the earthquake is just waiting to hit.

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