DECODING NE REGION’S SEISMICITY
By Dr Arati B Baruah
How well do we know Axom, how much do we know about the tectonic zones, ecosystem, geography and biodiversity? What about The Seven Sisters? The Seven Sisters additiolly have unique diversity, lowlands and highlands, beautiful landscapes, mineral resources and innumerable rivers. Still a lot of environmental arid ecological research needs to be done in this area actually in the Yarlung Tsangpoo Suture Zone. The new generation with roots in the North-East region of
India should be aware of the significance of this suture zone.
The Himalayan mountains were created by the collision of two continental tectoiic plates; the notable issue is that both had just about the same density. Therefore, subduction could not occur and one plate rose above the other and the Himalayan peaks soared high up. This mountain range is the youngest in the world.
Because of this collision, two sutures exist — the Indus River Suture Zone and the Yarlung Tsangpo Suture Zone. Both sutures have different properties.
In the non-professiol’s language, the pressure is very large at the Ladakh region of the Indus Structure; as a result, both of the plates have fused well, whereas there is loose coupling at the Yarlung Tsangpo region in the North-East. As a result, the foothills at Sikkim and Aruchal are hills soaring up like a wall, without any pyramidal or spherical bases and all these have loose soil. Erosion happens even when a road is built. Any bare piece of hill will make the whole hill wash away eventually. There is only a small region of Sivalik Range here and there.
That is why there are no big falls in Aruchal hills, verifying that no major rock formation exists there. The loose soil has not been under any high pressure or temperature and has not had any chance to form big pieces of hard rock. These properties make unsuitable conditions for river dams.
Even if the dam holds the hiIl, it may not hold in a major disaster. This may even be an earthquake of intensity 5 in the Richter scale, if the epicenter is origited in the hill or near it and pretty much on the surface. Part of the Assam region is on Seismic Zone 5, meaning it is prone to frequent earthquakes.
The loose coupling at Aruchal hills makes cracks possible on ground underneath, exposing basaltic salt, Arsenic, Lead etc having the chance of getting mixed with rainwater and thus getting into river water. The Yarlung Tsangpo region has not been explored scientifically. The whole suture region needs to be studied in a holistic way.
This suture region is partly in Tibet, partly in Myanmar and rest in the Seven Sisters. Myanmar, Tibet, Chi were not accessible for two decades and the irony is that nobody studied it well enough. Cloudburst situation is not studied in Aruchal and areas bordering Assam. Climate warning systems are not in place. The earthquake data and prediction comes from lIT Roorkee. However, local participation is essential. On another note, it has to be kept in mind that river Brahmaputra is still braided, its path is not stabilized and its freedom should not be taken away.
It is interesting that the great earthquake of 1897 was studied extensively; however, no holistic study has been done on the suture zone after the great earthquake of 1950. The earthquake of 1897 was so energetic that even big rocks floated up. It should be noted that the Everest peak is still rising and the peak at mcha Barwa is sinking. mcha Barwa is where the U-bend of Tsangpo happens and it is not too far from the Aruchal border. A research station near Lilabari needs to be set up and manned by local and intertiol scholars. lIT Guwahati’s participation is also very critical.
In Assam, Yarlung Tsangpo is known as Siang or Dihing. It is also called Zangbo in Tibet. The Siang started flowing down only 400 years or so. ‘Guru Charits’, the biographies of Shankardev and Madhabdev prove that Dihing was not flowing in those days. Possibly Yarlung Tsangpo was still a glacier then with a little leak, possibly a creek. The Three Gorges Dam is not very far from the North-East and its effect on climate in the region cannot be known accurately without the existence of comparable climate data. These data may be built from fragments.
I urge the new generation to learn about unique physical and geographical ture of Seven Sisters and the nearby region. Geological, and environmental professiols and researchers swarm there to do studies and research. There are a whole lot of environmental and ecological issues that needs to be sorted out for this region. New discoveries need to be made and then new insights will be emerging.
(The author recently retired as Engineer from Boeing. She has been studying the geology and associated aspects of the Brahmaputra river system for over a decade)