Tuesday, June 17, 2008

Is the Big One coming? - By Dr Sonam Wangyal


In 1994 Himal magazine (Kathmandu) ran an article by R. Bilham who is with the Department of Geological Sciences in the University of Colorado, USA. The periodical being a bit academic with a pricey tag attached to it the readership was restricted to a limited numbers of readers and therefore Bilham's article did not cause the tremor it could and should have. His article on the chances of a great earthquake in the near future in the Himalayan region shook me very strongly and the aftershocks kept on coming for many days. The essay was discussed with many of my friends and they lampooned me as a believer of a doomsday merchant. My knowledge of the mechanisms leading to an earthquake was at best scanty, and not knowing anything beyond what I had read there was really no way that I could hold the fort during our discussions. Nevertheless, Bilham's article still shakes me and after the recent Gujarat quake my mind is often troubled with tremors of a much higher intensity.

I shall endeavour to explain Bilham's hypothesis in the simplest language possible. The earth's surface consists of a number of large, rigid plates that move relative to one another and interact at their boundaries. Some billions of years ago the northward moving Indian plate slipped underneath the Asian plate pushing it both horizontally northwards and upwards. This led to the upheavals forming the Himalaya. The movement still continues and the convergence rate of India towards Tibet is 2cm a year and that is compensated by the Indian plate slipping under the Asian plate. However, if the slip does not occur it would mean that 2cm of convergence remains stored in the rocks as elastic strain. If no slip has occurred in 100 years the stored strain would be 2cm X 100 or 2m, in 200 years 4m and should the slip occur after 500 years the movement would be 10m resulting in a mega-quake of around M=8 (or a reading of 8 on the Richter Scale).

Any major compensatory movement requires an event exceeding M=7 and Bilham's observation is that in the Himalayan segment between Kathmandu and Dehradun has not had that for several thousands of years. The records show only two large earthquakes, 1803 and 1833, and Bilham does not believe they were great earthquakes else they would have caused massive devastations and the British administration would have records of the widespread destruction and the efforts taken for reconstruction. It therefore appears that the chance of a great earthquake is real since sometime in the future the plates must make an adjustment. Of course a pent up force of several thousands of years never undergoes adjustment in just one big shake-up but the alarming arithmetic is that even if 500 years were to be adjusted the movement would be 10m and such an event would measure Magnitude Eight on the Richter Scale.

To understand the effects of an M=8 plus event we can study the Great Bihar Earthquake of 1934, which did not evidently cross M=8, but came close to it. At 2:13 pm on 15 January two million square miles of northern India and western Nepal shook violently for 5 minutes. It took another 15 minutes for ceiling lamps to stop swinging in Calcutta and many more days for the dust to settle from the landslides in the mountains of Nepal. At Darjeeling a number of badly constructed houses totally collapsed, in many buildings cracks appeared or walls fell out and lots of bungalows were damaged by the fall of masonry chimneys crashing through the roofs. A ground fissure, over 300 yards long, appeared below the station yard in Tindharia and numerous breaches were seen all along the cart road. Should a Nepal-Dehradun great earthquake occur then north Bengal is assured of some consequences just as in the case of Bihar Earthquake. The point is not when it will come, since earthquakes are inevitable and necessary features of adjustment between the tectonic plates, but of our preparedness. Matters like maintenance of essential supplies, handling fire hazards, law and order problems, outbreak of diseases, post shock syndrome counseling and the eventual reconstruction are but a few of the many things that will need a look into. However, the greatest tragedy and hurt will be the loss of lives and that can never be restored but, and it is ,an important but, it can be prevented. Studies of earthquakes have shown that the major cause of deaths has always been due to poorly constructed buildings. Over the past few decades buildings have mushroomed all over the hills of Darjeeling, Kalimpong, Kurseong and Sikkim and are these structures built according to any studied and proven system of seismic resistant building codes or have they been built under outdated or whimsical codes will need to be considered seriously. That even these codes can be bypassed was proven a large building in Gangtok going down recently without the violence of an earthquake and such a vulnerable building could not be an isolated case. It is never too early to begin the process to prevent loss of lives but I could be talking to the wall, for all you know or care.


comment by praful rao

I need not introduce Dr Sonam Wangyal to anyone from this part of the world but for those who are abroad, Dr Wangyal is a physician firstly and a writer par excellence who writes on a variety of subjects.
While welcoming his article I would like to remind STH readers that we fall in ZONE IV of the 5 seismic belts and therefore as suggested by my young friend Niraj Lama, I feel STH can safely include earthquakes within its ambit.
In this connection I am reproducing an extract from a recent article "How prepared are we for Disaster?" by Patricia Mukhim, editor Shillong Times:-

"In its sheer ability to break its own rules the Urban Affairs Department (of Meghalaya) must be given a prize. Not a single builder adheres to the stipulated norms because the attempt to bribe the authorities starts from the time that the building permission is sought. All the commercial buildings in this city including those owned by powerful people would fail and earthquake test. The owners of those buildings do not care because they are landlords leasing the space out to lesser mortals. If the buildings collapse as they are wont to if a major quake hits the city, the building owner will be somewhere else while all the tenants and other members of the public who may be shopping will be buried under the debris.

What is the use of having a department that is creating more man-made disasters than solving them? Here I am talking of the Urban Affairs Department and its other arms as well as the State PWD. The latter as I have always maintained have no pride in their work. The former specialises flouting the rules it makes. Can the PWD point to one building which will withstand an earthquake? If there is one such we would like to know which one. Whenever a techno-legal regime becomes operational in Meghalaya can the government bring down all those badly constructed buildings that are not earthquake proof?? No it cannot. So they will remain towers of corruption for generations."


Malay said...

Well! Dr. Wangyal has rightly pointed out that the Darjeeling-Sikkim region is an extremely vulnerable region for great earthquakes (> 7 on Richter Scale). Roger Bilham published a paper in Science in 2001 which identified several regions in the Himalaya that were overdue for a great earthquake. Darjeeling-Sikkim region was one of them. If the arguments he put forward in the paper is true, Darjeeling-Sikkim should be in Seismic Zone 5 not Zone 4. I have been using high precision GPS to make measurements and test Roger's hypothesis since
2000 in Darjeeling-Sikkim and the results are starting to make sense. Like Dr. Wangyal says, it is not a question of if but when. When the big one comes we in the Darjeeling-Sikkim hills will not stand a chance. The concrete we have constructed over our heads will collapse and bury us. Our roads are such that equipment needed to lift the concrete slabs will not make it to most places. The earthquake will trigger landslides all over. There will be mass destruction like Kashmir, like Bhuj, like China, like Indonesia. We are completely unprepared for anything like this.
There have been many articles in the past (I personally helped write the article Time Ticking Away! in the Statesman couple of years back to highlight this issue)that point this out. However, Dr. Wangyal, this time we are not really concerned about the effects of distant earthquakes in Darjeeling-Sikkim (like that in 1934). We are concerned about a 1934 like epicentre being located in Darjeeling-Sikkim. May god have mercy on our souls when that big one comes!

Darjeeling Brew said...

Indeed I also remembering the - sorry for the metaphor - but an earth shattering report, at least for us, when Prof Bilham came out with it. It seems like such a long time ago. Sadly, despite all the warnings it is business as usual. Let me remind ourselves of yet another long-stated scary fact that elicits hardly any response - Darjeeling is the world's most densely populated mountain region: over 10,000 people per sq km. And that was 2001 census. Almost a decade ago.That's why lets get that damn rabbit-tendency under control!!!