Overview | Earthquake | Drought | Fire | Flood & Cyclones | Landslide & Soil Erosion | Volcano
Earthquakes in Delhi:
A capital problem
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.