Delhi is earthquake prone

Delhi is earthquake prone

The Bhuj earthquake was something of a watershed in Indian disaster preparedness. Several state governments, most so in the Northeast, and various central ministries were shocked into a comprehension of the dangers. However, national capital New Delhi, which is under perpetual latent seismic threat, is blissfully unattended. Neither the local nor the Union government has initiated any measures to protect the city.

It is true that Delhi is unlikely to be at the epicentre of a moderate to large earthquake. The highest earthquake magnitude experienced in Delhi in about a century was on July 27, 1960. It registered 5.6 on the Richter scale. Some buildings in the New Delhi area were partially damaged during that quake. A seismic damage survey, by the Central Public Works Department (cpwd), put the damage at about Rs 5 lakh.

In seismological lexicon, a moderate or major earthquake (magnitude 7.0 or more) causes two types of damages. The first, commonly known as epicentral damage, is confined to a 50-70 km radius. This damage is caused by 'body waves', which travel from the epicentral area to the surface of the earth through the body of the earth. Once these waves reach the surface, they are transformed into 'surface waves' or 'long period surface waves'. These waves travel along the surface of the earth, and their amplitude is the maximum at a distance of 200-400 kilometres (kms) from the epicentre. Surface waves cause the most damage to tall structures (height: 15 metres (m) or above). Single storey or even 2 to 3 storey buildings are not affected by surface waves.

The Michoacan earthquake (8.1 on the Richter scale) in Mexico on September 19, 1985 brought home the destructive impact of surface waves. The epicentre was 320 km away from Mexico City, which suffered the most damage. Then there was the Bhuj quake of January 26, 2001 (also a magnitude of 8.1). Tall buildings in Ahmedabad, located about 310 kms away from the epicentre, suffered heavy losses.

The aftermath of these quakes holds a lesson for Delhi, which is located at a distance of 280-350 kms from the Himalayan ranges. Seismically speaking, the main boundary thrust fault (mbt) of the Himalaya, which runs from Kashmir to Arunachal Pradesh, is highly active. This zone has produced earthquakes that register over 8.0 on the Richter scale: in Assam on June 12, 1897; in Kangra on April 4, 1905; the Bihar-Nepal quake of January 14, 1934; and the devastating Assam quake of August 15, 1950.

Delhi is located within a distance of 200-400 km from different locations of the mbt. An earthquake over 7.0 in the Shimla to Dehradoon/Pithoragarh (or western Nepal) ranges will cause tall structures in Delhi to fall like a pack of cards. And the number of multi-storeyed buildings in Delhi has risen sharply in the last three decades or so. Several hundreds of buildings are at risk from surface waves in case of a quake in the mbt. The threat is compounded by fragile geological formations, total non-observance of Bureau of Indian Standards (bis) norms, poor quality control and, of course, the irregular manner in which maps and structural designs are passed at the municipal level.

The question, though, is: can we hope to achieve seismic safety in Delhi? The answer is: yes. Solution one: strengthen existing buildings. bis codes specify various ways of doing this. There should be legislations that make seismic strengthening compulsory. Limits should be set based on the age of the building, and appropriate time limits should be set for execution of the strengthening (not more than a year).

Secondly, all maps and designs for new constructions should strictly follow bis norms. Further, completion certificates for high-rise buildings should be staggered. Part completion certificates, issued every two or three floors, could regulate construction through the whole process.

And lastly, it is important to create awareness about earthquakes. This could help reduce loss of human lives, if not property. The government could initiate training at various levels: for 'vips'; decision-making level administrators; implementation level administrative cadre; educational institutions; and the common person. The media must also play a role in disaster mitigation. Information-based articles and programmes could be far more constructive than covering post-quake carnage.

In Japan, for instance, September 1 is observed as natural disaster mitigation day. The big Tokyo earthquake (8.5 on the Richter scale) took place on this day in 1923. The entire nation takes up the seismic drill -- rushing ambulances, fire fighting squads, medical teams. The result: very few deaths during subsequent quakes. Quite unlike October 29, which is similarly observed in Orissa (post the Orissa cyclone of 1999): politicians and administrators deliver talks and lectures, and little else.

Arun Bapat is research seismologist based in Pune