Every natural calamity has some new lesson to teach us. The last two — the tsunami of December 26, 2004, and the heavy flooding of Mumbai on 26th July this year brought their own insights. The tsunami alerted us to the need to urgently protect our coastline from tidal waves — as much as we can; the latter taught us that we can ignore the state of urban drainage only at our peril.
Similarly, the October 8, 2005, earthquake — with its epicentre near Muzaffarabad in Pakistan — has brought with it some new lessons. The Pakistan earthquake has not spared India either. It may be worth recalling that the January 26, 2001, Bhuj earthquake was strongly felt in the Sind province of Pakistan and that it had claimed about 50 people in Sind at that time.
The similarities do not end here. The structural damage that surfaced in Pakistan this time and in India were also almost similar. ‘Margala’, the 11-storeyed building in Islamabad — located at a distance of about a hundred kilometres from the epicentre, suffered heavy damage. We could have been looking at the buildings that collapsed in Ahmedabad, four years ago. Remember ‘Shikhar’, a 11-storeyed building in Ahmedabad which collapsed like a pack of cards at that point? It is significant to note that a number of other structures in the vicinity of ‘Margala’ and ‘Shikhar’ were either not affected, or had suffered only minimal damage. There is in the fate of these two buildings a great deal of information that structural engineers in India and Pakistan should try to decode, so that they can come up with better designs for high-rise buildings in areas that are earthquake-prone.
Against this background, let us examine the fate of conventional structures. Press reports and television coverage indicate that there has been extensive damage in the mountainous areas of this region. The area in the vicinity of earthquake epicentre is situated at an altitude of 2,000 to 3,000 meters. Seismic vibrations have more amplitude at higher elevations. For example, take a 30-storeyed building. It will have the least vibrations at the level of the ground floor but, as you go higher, the amplitude of the vibrations increase. The earthquake damage in Baramulla, Uri, Poonch, and so on, which are located at heights of about 1,500 to 2000 metres, and at a distance of about 60 to 90 km from the epicentre, was therefore more severe, as compared to the damage at Islamabad or Haripur, which are at a distance of about 60 to 90 km, but situated at an elevation of about 500 metres or so.
The effect of height on the damage perpetrated by the earthquake on buildings was very clearly seen. When one side of a house rests on a hill or mountain, the house has either not suffered at all, or the damage done to it has been minimal. This is due to the fact that the house does not vibrate as a single unit. It forms a small part of the entire mountain.
This can be better understood if you consider the example of Shimla. We have tall buildings in Shimla. Some of the buildings here may have five or more floors, but invariably one side of these building is not a man-made wall but the mountain itself. Such buildings will not suffer heavily during an earthquake. However, tall structures — isolated and open on all sides —are likely to suffer heavy damage. The High Court and Medical College buildings in Shimla should be scrutinised and studied from this angle.
One of the more interesting lessons to emerge from the Pakistan earthquake s, incidentally, an exceedingly useful one for the armies of India, Pakistan and China. It is most unfortunate that some jawans of the Indian army died because their bunker had collapsed after the earthquake. The Pakistan army also suffered many casualties. Ironically, the bunker is meant to be one of the safest places to take shelter in during military operations. Even deep penetrating bombs find it difficult to go through their covers, made of reinforced concrete and steel. A soldier is supposed to be safe in his bunker. He gets his food, water, shelter, bed and rest in it. But the experience of the latest earthquake has shown that while the bunker may give maximum protection from aerial bombardment, it will not provide even short duration protection if the attack comes from the ground. This means that now army engineers must get busy in designing bunkers which will not collapse during earthquakes. They should ensure that suitable modifications are made in design so that these structures meant to protect soldiers do not sink or collapse on them. This earthquake needs to be studied in terms of bunker design.
Let’s go to our next lesson — an important point about about sediment in rivers. When a moderate to heavy earthquake (with a magnitude of 6.5 or more) occurs in the catchment area of a river, a huge amount of soil, loose and fragile rock, and other material falls into the river, increasing its sediment content greatly. In hydrological terms, this is known as "fully charged". The River Indus and a number of rivulets have been charged to their maximum sediment-carrying capacity. If there is a dam downstream then the entire sediments are deposited in the reservoir. The flow of seismo-sediments in the river can be observed for six to ten months after an earthquake. This effectively reduces the useful life of a reservoir.
This means that the sediment deposits in various dams will now have to be examined. The January 1975 Kinnaur earthquake in Himachal Pradesh — with a magnitude of 6.5 — generated a huge amount of sediments which were terminally deposited in the Bhakra reservoir. Now both India and Pakistan need to examine the feasibility of building check dams upstream of the existing dams, so that the seismo-sediments are deposited in them and only water flows downstream.
These are just some of the lessons we can glean from this tragedy. There are, without doubt, several more. All these need to be studied so that we in this region can be better prepared to face reversals of this kind. The situation, in fact, warrants an extensive field damage survey on the part of both countries. Let us turn our grief into a learning experience.
The writer is a senior research seismologist. He was a former chief research officer of the earthquake engineering
