Earthquakes in Delhi: A capital problem
As per the Indian seismic zone map, Delhi and its surroundings are placed in what is termed, seismic zone IV (zone V implies the highest and zone IV is reasonably expected to sustain a shaking of Modified Mercalli Intensity VIII (on a scale of I to XII) in the future. MM Intensity VIII has been defined as:
"Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse; very heavy in poorly built structures. Panel walls thrown out of framed structures. Fall of chimneys, factory stacks, columns, monuments, and walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motor cars disturbed,"
Considering many other day-to-day problems of a mega city like Delhi (traffic, environmental pollution, water and power shortage, etc.), the issue of seismic risk for Delhi has not drawn the attention that it deserves. This article is an attempt to put the issue of earthquake problem for Delhi in perspective.
Most death and destruction in an earthquake are caused by collapse of man-made construction. Since the mankind is far from the possibility of being able to successfully predict earthquakes, the only option is to build or houses and other facilities to survive earthquake. Clearly, engineers have to play a major role by ensuring that (a) new constructions are earthquake resistant, and (b) the existing structures are strengthened appropriately to be able to withstand earthquake shaking.
Great earthquakes disasters
Housner (1998) has articulated the issue of great earthquake disasters in a very simple way. Recall that in the 1976 Tangshan (China) earthquake (magnitude 7.8), as per official estimates about 243,000 persons died out of 1,000,000 population while the unofficial estimates on casualty are much higher. This earthquake occurred in a place that was considered to have a rather low seismic hazard and therefore the constructions there were not made earthquake resistant. However , even smaller earthquakes can cause great disaster. For instance, in the 1960 Agadir (Morocco) earthquake resistant. However, even smaller earthquakes can cause great disasters. For instance , in the 1960 Agadir (Morocco) earthquake (M5.7) about 10,000 persons died out population of 30,000. Nearer home, during the 1993 Killari (Latur) earthquake (M6.5) in Maharashtra (India), more than 30% population was killed in several villages. Again, killari (Latur) region used to be considered safe from earthquake view point and placed in the lowest seismic zone (zone I)
As put by Professor Housner, a great disaster may occur if three conditions are met: (a) an earthquake of sufficiently large magnitude, (b) occurrence of the earthquake close enough to a population centre, and (c) the population centre having buildings which are not earthquake resistant. The question we must address is: is there a possibility of these conditions being met for Delhi at some time in the future? In view of huge population and the economic-cum-political significance of Delhi, occurrence of such conditions can cause not just a great disaster; but a mega disaster.
Past earthquakes around Delhi
A detailed seism tectonic discussion of the area is beyond the scope of this article. Yet, it will be of considerable interest to see if Delhi has sustained strong earthquake motions in the past. As poer Iyengar (2000) damaging earthquakes have occurred around Delhi since ancient times. He points out that the great epic, Mahabharata mentions about earthquakes during the war at Kurukshetra (Circa 3000 BC?). More recently, damage to Delhi in the 1720 earthquakes (intensity IX in Delhi) is well discussed by Kafi Khan (Iyengar, 2000). Tandon (1953) mentions of damage to the Qutab Minar during the 2803 earthquake near Mathura.
Srivastava and Roy (1982) discuss several more earthquakes in Delhi region. These include: (a) earthquake of year 893 or 894 (Intensity XI XII) which took place not far from Delhi in which many persons died; (b) earthquake of 22 March 1825 near Delhi Intensity VII; earthquake of 17 July 1830 near Delhi (Intensity VIII); and (d) earthquake of 24 October 1831 near Delhi (Intensity VI)
Delhi has also sustained earthquake damage in more recent times. For instance, Srivastava and Somayajuluy (1966) mention of (a) Khurja earthquake (M6.7) of 10 October 1956 in which 23 persons were killed in Bulandshahr and some injured in Delhi; (b) M6.0 earthquake of 27 August 1960 near Delhi wherein about 50 persons in Delhi were injurred; and (c) an earthquake near Moradabad on 15 August 1966 that killed 14 persons in Delhi. Iyengar (2000) also mentions about damage to one of the minarets of Delhi's Jama Masjid during the M4.0 earquakes on 28 July 1994.
Most recently, the 1999 Chamoli earthquake (M6.5) took place about 280 km from Delhi. Such a moderate earthquake does not normally cause damage at such large distance. And yet, several buildings in Delhi sustained non-structural damage possibility due to peculiar geological and geotechnical features if this area. Fig. 1 shows damage to the gound storey partion walls of a multistory apartment building in the Patparganj area. Collapse of a few architectural fins at the Shastri Bhawan during this earthquake is shown in Figs.2 (a,b). In 1985, an earthquake about 400 km from Mexico city caused very considerable damage and deaths in Mexici city, primarily due to the peculiar site conditions there. The Chamoli earthquake effects in Delhi indicate that there is real possibility of a large earthquake in the Himalaya causing considerable damage to Delhi.
It is therefore seen that Delhi is prone to severe earthquake damage both by nearby earthquakes and by large earthquakes occurring in the Himalayas. The scientists and engineers need to urgently take up detailed investigations to develop a more quantitative understanding of the seismic hazard faced by Delhi. Unfortunately, not many such studies have been carried out so far. For instance, paleoseismics studies to locate major earthquake events of the past, e.g., the 1720 and the 1803 events, would add significantly to the hazard evaluation. Due to its complex geological setting, some areas of Delhi are likely to sustain much higher levels of damages than the others and to evaluate this, detailed microzonation studies are needed. (e.g., Iyengar,2000).
Current status of building stock
The first code of practice for earthquake resistant design was developed in India as early as 1930's after the 1935 Quetta earthquake (e.g., Jain and Nigam, 200). The Bureau of Indian Standards developed its first code on aseismic design in 1962 (IS:1893-1962). However, till date there is no legal framework to require that all constructions in Delhi must implement seismic code provisions. The results is that most buildings in Delhi may not meet codal requirements on seismic resistance. Moreover, even if from now on we somehow ensure that all new construction will be earthquake resistant, there still will remain a very large inventory of old buildings that will be deficient for seismic safety. We need to develop a rational seismic retrofitting policy, first for the government- owned buildings and later for the private constructions.
As per Vulnerability Atlas of India (1997), for shaking intensity VIII, 6.5% houses in Delhi have high damage risk , and85.5% houses have moderate damage risk. These estimates are based on very simplistic assumptions. Systematic studies are needed on vulnerability of different types of constructions in the area. This will require experimental studies to evaluate strength, stiffness and ductility of different types of constructions as well as as analytical studies such as the Push Over Analysis. Experiences of past earthquakes both in India abroad have clearly outlined the vulnerability of multistorey reinforced concrete buildings if not designed and constructed correctly. Huge number of multistorey reinforced concrete buildings in Delhi, particularly those with open ground storey to accommodate vehicle parking, could also pose a major challenge in the event of a strong earthquake.
Infrastructure and other implications
Delhi is currently passing through a major infrastructure development phase with a large number of bridges, flyovers and the metro project under construction. After a severe earthquake, the transport infrastructure is earthquake resistant and the old one is seismically retrofitted. Indian seismic code (IS:1893-1984) is not applicable for major projects which require special studies on seismic design criteria. Moreover, the Indian seismic codal provisions on bridges as these exist today are obsolete and inadequate (e.g Jain and Murty, 1998).
Earthquake disaster in Delhi has the potential to go well beyond the statistics of deaths and injuries. Such a disaster in the country's capital, which also happens to be a major commercial and industrial centre, will have huge economic and political implications which will affect the entire country and not just the population of Delhi. This adds an extra dimension to the earthquakes problem for Delhi.
Plan of action
A valid question at this stage will be: should one be concerned about an earthquake which has a very low probability of occurrence, when Delhi faces so many day-to-day problems of environment, noise, traffic, water and power shortage, etc? The consequences of a severe earthquake to not seriously address the problem. Put it differently, considering the potential for a mega disaster, we cannot afford ignore the earthquake problem.
As a first step towards earthquake disaster mitigation the problem must first be recognized and quantified. Herein lies the first challenge: to discuss and debate the problem of this kind on a rational basis and yet not cause panic. Once the problem is identified and an action plan agreed upon, the need will arise for a political and administrative will to implement the action plan. It must be emphasized that the problem requires huge efforts and is well beyond a few individuals or a few organizations. Numerous scientific and engineering activities will have to be initiated simultaneously before we can even quantify the size of the problem by way of seismic risk scenarios.
As of now, there are too few experts in this subject for a large country like India. We must focus our attention to the institutionally and manpower development at all levels. Extensive studies are needed for seismic hazard evaluation for different parts of Delhi and vulnerability assessment for different kinds of constructions; using these, seismic risk evaluation for Delhi must be carried out. Manuals need to be developed outlining methodologies for new constructions and retrofitting of old ones. A strong legal and enforcement framework with appropriate incentives and punitive measures is required together with awareness programmes for general public. All these components must be taken up simultaneously; ignoring one aspect for the other could be counterproductive.
Summary and conclusions
Delhi has had many damaging earthquakes in the past and is placed in a high seismic zone (zone IV). Delhi is prone not only to damaging earthquakes in or near Delhi, but due to its peculiar geological setting it could also sustain strong shaking due to a large earthquake in the Himalaya. Unfortunately, most buildings in Delhi may not meet Indian standards on aseismic constructions and may be considered deficient from seismic safety view point. Thus, there is a real potential for a great earthquake disaster in Delhi, the implications of which go well beyond casualties because of its political and commercial significance.
There is an urgent need for healthy debates on seismic risk aspects of Delhi and for reasonable assessment of the problem. Studies are needed on seismic hazard evaluation for different types of construction. Using these, seismic risk scenarios must be developed and implementation strategies chalked out for new and old constructions. The efforts required are truly multidisciplinary and should include components on technical training, institutional development, development of technical manuals, legal and enforcement aspects, and public awareness programmes. Most importantly, we need the political will to handle this problem and the biggest challenge perhaps lies in drawing the attention of political leadership to this problem when the city faces many other urgent problems.