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25 Apr 16 08:55

During
last week, Delhi experienced two earthquake tremors and one of them forced the Delhi metro to stop their services. This should not lead to the notion that these two earthquakes occurred at or near Delhi. The epicenter of the first earthquake (magnitude 6.6) was in Afghanistan (near the north-western region of India) and the second one (magnitude – 6.9) in Myanmar (near the north-eastern region of India). However, the interesting fact is that even though these earthquakes were at a distance of 1000 and 1800 km from Delhi, they were felt widely and created panic in the city.

Why has this happened? There no simple answer to this question. One of the main reasons for these far distant earthquakes being felt in Delhi is the presence of soft alluvial soil deposits. These soft soils amplify the earthquake waves (vibrations) and in many parts of Delhi, the thickness of soil deposits are more than 100 meters. Moreover, the natural frequency of vibration of these soils closely matches that of high-rise buildings. This means that the effect of the ground shaking will be more predominant in high-rise buildings than for a single or two-storied building. In addition to these, we need to take into account the huge share of unreinforced masonry structures in Delhi, which are highly vulnerable to earthquakes, as well.

Though any major earthquake (magnitude > 8.0) has not hit Delhi in the past, such an event cannot be ruled out in future. Researchers who are working on the Himalayan seismicity have pointed out the existence of a central Himalayan seismic gap. Seismic gaps are those areas, where the deformation has been occurring due to the plate movement, but there have been no major earthquakes in the recent past to release this accumulated energy. These regions are considered as high risk areas as the likelihood of big earthquakes in future is very high.

Since we will not be able to predict, warn or prevent an earthquake, the way forward in reducing the impact of an earthquake, when it does occur, is through better preparedness. There are many measures taken by the government in assessing the seismic hazard, soil characteristics and preparation of maps showing vulnerable areas in Delhi. However, one can question as to how much of these research findings are being translated into actions. It is key that going forward, seismic code provisions need to be enforced rigorously. So far, this has not always been the case. The government will have to ensure that the provisions of the code and research findings are being followed in all construction activities in areas, which are vulnerable to earthquake damage.


Category: Climate/natural disasters: Disaster risk, Earthquakes

Location: New Delhi, India


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