TAKING A COMPREHENSIVE VIEW OF QUAKES

The tragic Nepal quake is an opportunity to learn and understand the threats of great temblors.

The Nepal earthquake of April 25 is the largest in the Himalayan region since the 1934 quake which measured 8.2 on the Richter scale and destroyed not only parts of central Nepal but also the plains of northern Bihar in India. Mahatma Gandhi, shaken by the Bihar tragedy, wrote in the Harijan that the earthquake was “providential retribution to India’s failure to eradicate untouchability”. Although this statement dismayed the rationalist in Jawaharlal Nehru, it was Rabindranath Tagore who dared Gandhi by sending a letter to the Harijan saying, “Physical catastrophes must have origin in physical facts”.  When Tagore, always far ahead of his times, made this insightful statement, the science of earthquakes had not developed. It was only in the 1960s that plate tectonics explained the origin of earthquakes.

Like other Himalayan quakes, the Nepal temblor is a dramatic manifestation of the ongoing tectonic convergence between the Indo-Australian and Asian tectonic plates that have built the Himalayas over the last 50 million years. A product of millions of years of crustal shortening, the Himalayas are under immense tectonic stress and occasional temblors. The last 200 years in the region have seen four great earthquakes. But central Himalaya has been an exception, researchers warn, and is considered to be susceptible to great temblors.

The Nepal quake is a painful reminder of what is in store for the communities that live in the region and in the adjoining Indo-Gangetic plains. Sadly, lessons after such tragic events are often short-lived in public memory. This quake, too, opens an opportunity to learn and understand the threats of great earthquakes which may occur in the vulnerable region of north India and we must retain these lessons.

Why was it so devastating?

The Nepal earthquake was devastating due to many factors. The source of the quake was shallow and the fault plane extended right up to densely populated Kathmandu. Added to this, Kathmandu is on a primitive lake basin that amplifies seismic wave energy. The slip of 1 to 3 metres recorded along the 160-km-long rupture showed strain built up over a century. Research implies that this segment has seen no great earthquakes in the last 700 years. Thus, the unspent accumulated slip needed to be released through this quake and will further be released through future quakes. This means that the segment, which includes parts of Uttarakhand, is capable of witnessing more damage. The Nepal earthquake rupture probably did not move towards the Indian plains in the manner that it did in the 1934 quake. But India may not be so lucky next time.

As India’s northern territory is interfaced with a 2,400-km-long seismically potential Himalayan arc, it needs to develop a workable strategy to lessen the impact of earthquakes in populated areas. The ability to minimise damage and prepare for the aftermath of an earthquake has to come from a deeper insight on earthquake processes, and analyses of large amount of data that will enable us to study the source and effects of a quake. The latest advances in seismic sensor technology, data acquisition systems, digital communication and computer hardware and software facilitate developing real-time earthquake information systems. In rapid data dissemination, India needs to learn from the U.S. Geological Survey. India’s close proximity to an active plate boundary makes rapid dissemination of seismic data necessary. India should give priority to not only install but also sustain dense networks of observatories for both weak and strong motion data — like Japan, Taiwan and the U.S. do. Using such

data to understand source characteristics is one way of helping the seismological community understand and constrain the manner in which faulting occurred and its probable extent. This data can also be exploited to develop an earthquake alert system, which essentially uses the travel time difference between the body waves and surface waves. For example, a resident in Delhi can be given a few minutes of alert on a major Himalayan earthquake, originating about 250- km away, using the difference in travel time lag between the body waves and the damaging surface waves.

Better building practices

This would also allow us to quantify reasonably the expected ground motion in any region, which can be the basis for designing earthquake-resistant buildings. Our experience in the Himalayan towns, of moderate earthquakes (the 1996 Chamoli and the 1991 Uttarkashi earthquakes, for example), indicates that better building practices are major factors in lessening the impact of destructive events. Another learning experience is the historical example of the 1803 Uttarkashi earthquake which generated distant liquefaction in Delhi and Mathura and triggered landslides that smothered Himalayan villages. The top part of Qutb Minar toppled, too.

Yet, we haven’t made headway in risk assessment, the core database for disaster management. Risk assessment requires intense field studies, developing models that use data on the frequency and severity of a particular type of natural hazard that strikes an area, and combining this information with the nature and class of vulnerable structures. It would be prudent to calculate the earthquake risk in the region if such an earthquake were to happen in Uttarakhand. According to a study in 2000, if a 1905 Kangra earthquake were to occur today in the Himalayas, direct losses would amount to Rs.51 billion, cost around 65,000 lives and 4,00,000 houses. If all the houses were made earthquake-resistant, this would reduce to Rs.19 billion. The extra cost of retrofitting would be about Rs.19 billion, the loss of life would be reduced to one-fifth and the number of ruined houses would be reduced to one-fourth. It is also true that many new buildings in earthquake-prone areas do not comply with seismic codes because certificates of safety are easy to procure. People living in the hills should be encouraged to follow traditional building practices rather than concrete monstrosities. Laurie Baker, the legendary architect, had some meaningful suggestions to strengthen traditional houses in the Himalayas. Some of his pencil sketches, preserved in archives, will be useful in this regard. But it is also true that traditional stone houses using rounded boulders in the Himalayas are known for very poor performances during the earthquakes. The Indian Standard IS: 13828 (1993) suggests several methods to improve their design and construction to make them earthquake-resistant.

We need to focus not only on earthquake engineering but also on seismological research. For this to happen, along with an ambitious vision for a seismic network, we need trained manpower to conduct high-level seismological research. One way to reinvigorate both institutional and university-based research is to develop a strong framework where both can interact. Research without teaching and teaching without research are failed models, but we continue to follow this path. Seismology is a global science and interacting with the global research community should be encouraged. Our researchers must conduct research on equal footing with the international community. The Himalayas are a fantastic natural laboratory where earth processes can be captured live for new insights. Tackling future natural disasters will require a healthy mix of technology, scientific studies, trained and committed manpower, professionalism and the development of engineering skill and public awareness.

Courtesy : The Hindu

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