When the ground shakes

THE YOUNG SCIENCE of seismology - dating back no more than a century - has added greatly to our understanding of earthquakes. But in spite of all the impressive advances, the uncertainty about when and where the Earth will next release its destructive energy from within remains just as strong as it has been throughout human history. After the Gujarat earthquake, reports have begun to appear of seismic activity in Kutch in late December which was not acted on by the State Government. But around the world 50,000 incidents of seismic activity that can be felt by humans take place every year, of which only about 100 cause some damage and just one causes widespread devastation. It is therefore impossible to organise a mass evacuation of human populations whenever there is the first sign of seismic activity. What science can now tell us is which areas on the earth's surface are more prone to seismic activity. This knowledge was available but not used in Kutch. Nor has it been used in the sub- Himalayas and Assam, the regions more commonly associated with earthquake dangers in India.

The subcontinent is an area of relatively high seismic activity since the Indian plate continues to move ahead by 5 cm a year and consequently exerts pressure on the Eurasian plate. Kutch does not lie in this zone but it is identified in all seismic maps as a region highly vulnerable to extreme seismic activity. While it is still not known if last week's quake was caused by shock waves from the fault under the Allah Bund (the scarp that emerged after the 1819 Kutch quake) or from the Narmada Son Lineament, it was in retrospect an earthquake that was going to happen sooner or later. What frustrates seismologists is that while the location of future events of major seismic activity can be identified with some probability, the probability of success in locating their timing - which is what people and Governments need to know - remains extremely low. Among the many approaches that have been experimented with, the more unusual one developed in China is studying the behavioural patterns of birds and animals, which have been observed to show heightened and abnormal activity on the eve of a major earthquake. Although even in the early 1970s the Chinese claimed some success in this field, the technique failed in predicting the Tangshan earthquake in 1976 in which 250,000 people died. The theory of dilatancy, or relating physical patterns to the dilation of underground rock formations, holds more promise. But the truth is that even the most sophisticated technology does not provide much of an answer. In spite of all the seismic monitoring of Japan (which along with California is the most closely watched region in the world because both are known to be sitting on major faults), there was no prior warning of the Kobe earthquake of 1995 which measured 7.2 on the Richter scale and took 5,000 lives.

Seismology still cannot make accurate and useful predictions of where the next earthquake will strike. But since geology and seismology can and have mapped India into zones of varying seismic activity, it should be possible to make an assessment of the risk of seismic activity and accordingly strengthen building structures to prevent the tragedy of the kind that has befallen Gujarat. For years the assessment has been that a major earthquake will strike India. But though Kutch was in the danger zone it was not this region but the sub-Himalayas and Assam which have been on the radar of seismologists. North and Northeast India remain highly vulnerable to a major quake. The first lesson of Gujarat must be that the existing structures in these parts of India should be strengthened for protection against major tremors and new buildings should be designed so that they can withstand events of extreme seismic activity. The country cannot go through the agonising trauma of another Gujarat.

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