Earthquake: Some Indian cities, other parts of the world may now be vulnerable,scientists fear
Seismologists have been discovering unknown facts about the Indian sub-continent, primarily because of increased seismic monitoring.
By Hari Pulakkat, ET Bureau | Updated:
Residents of the east coast of the United States generally think of themselves as safe from earthquakes. This feeling was given a jolt on August 23 when a 5.9-magnitude earthquake hit near the town Mineral in Virginia. Nobody died, but a nuclear reactor there shut down by itself as its electricity supply tripped. This nuclear plant was designed to withstand earthquakes of magnitude up to 6.2 on the Richter scale. The designers of the plant had thought that Virginia would not experience stronger earthquakes, but the tremor last week was uncomfortably close to the limit. The plant was among the 27 nuclear plants in the east coast that registered unusual events because of the earthquake.
This earthquake has once again thrown open the possibility that earthquakes can strike anywhere any time, and not just in areas that are known to be at high risk. In the past few years, seismologists have been discovering surprising facts about dormant faults and places with no geological faults. Exactly three years ago Columbia University seismologists had found out that New York had more seismic activity than previously thought, and it posed a small danger to the nuclear plant there. In April this year, seismologists at the United Nations Development Programme (UNDP) had warned that 50% of the world's supercities faced high earthquake risk. And there are some seismologists who think that the world has entered an extended phase of heightened seismic activity.
Clash of Plates
Seismologists have recently been discovering unknown facts about the Indian sub-continent as well, primarily because of increased seismic monitoring. The northern part of the country, the foothills of the Himalayas in Uttaranchal, is known to be awaiting an earthquake of magnitude 8 on the Richter scale. This is not surprising because the Indian subcontinent is pushing at the Asian plate there, and one expects large earthquakes at plate boundaries. But geologists have also discovered large stresses in central India and think that there could be future damaging earthquakes in places that have not recorded earthquakes so far. And also that even cities in South India are not free from risk. What would happen if a moderate earthquake strikes Bangalore?
Earthquakes usually happen when two tectonic plates push against each other. All the high-risk areas are along fault lines, or boundaries between two plates. But about 10% of the earthquakes are called intraplate earthquakes, or those occurring far away from plate boundaries. The Bhuj earthquake that devastated Gujarat in 2001 was an intraplate earthquake. So was the Virginia earthquake last week. Intraplate earthquakes are not understood well and not studied as well as the interplate earthquakes, yet once in a while they strike with catastrophic effect. In 1811 and 1812, two earthquakes of magnitude larger than 8 had struck at New Madrid in Missouri. These earthquakes devastated the region, created a new lake and changed the course of the river Missouri. In a few months, we reach the 200th anniversary of this earthquake. What if such an earthquake happens now?
Ground Beneath Our Feet
The New Madrid earthquake was the worst intraplate earthquake known so far. Intraplate earthquakes of such intensity are rare. Moreover, they occur at places where the earth’s crust is weak. The crust at central US, where New Madrid lies, is stretched thin by tectonic forces and thus not strong enough. Gujarat, another site of intraplate earthquake, also has a crust weakened by several now-quiescent faults.
Central India, on the other hand, has a high degree of bulge from flexure due to stress built up from the Himalayas. Recent studies have discovered this stress as much as 1,000 km south of the Himalayas. The 1993 Latur earthquake had happened at a region of stress. This earthquake, measuring 6.4, had shocked seismologists as they had never expected an earthquake to happen there. The lessons of the recent spate of intraplate earthquakes are clear. A large portion of India lies in hazardous zones, a fact that is relevant to rapidly expanding nuclear power industry in India.
Given the ability of intraplate earthquakes to surprise, one should expect damaging earthquakes at many places in the country. Even southern cities are not entirely safe, although seismologists do not expect even moderate earthquakes to happen there. Many high-rise buildings are built without following any codes. Especially vulnerable are those on stilts and those built on or near dried lakes. The city of Bangalore is full of such buildings. So are several other cities in the country. Are we inching towards one of our worst natural disasters?
This earthquake has once again thrown open the possibility that earthquakes can strike anywhere any time, and not just in areas that are known to be at high risk. In the past few years, seismologists have been discovering surprising facts about dormant faults and places with no geological faults. Exactly three years ago Columbia University seismologists had found out that New York had more seismic activity than previously thought, and it posed a small danger to the nuclear plant there. In April this year, seismologists at the United Nations Development Programme (UNDP) had warned that 50% of the world's supercities faced high earthquake risk. And there are some seismologists who think that the world has entered an extended phase of heightened seismic activity.
Clash of Plates
Seismologists have recently been discovering unknown facts about the Indian sub-continent as well, primarily because of increased seismic monitoring. The northern part of the country, the foothills of the Himalayas in Uttaranchal, is known to be awaiting an earthquake of magnitude 8 on the Richter scale. This is not surprising because the Indian subcontinent is pushing at the Asian plate there, and one expects large earthquakes at plate boundaries. But geologists have also discovered large stresses in central India and think that there could be future damaging earthquakes in places that have not recorded earthquakes so far. And also that even cities in South India are not free from risk. What would happen if a moderate earthquake strikes Bangalore?
Earthquakes usually happen when two tectonic plates push against each other. All the high-risk areas are along fault lines, or boundaries between two plates. But about 10% of the earthquakes are called intraplate earthquakes, or those occurring far away from plate boundaries. The Bhuj earthquake that devastated Gujarat in 2001 was an intraplate earthquake. So was the Virginia earthquake last week. Intraplate earthquakes are not understood well and not studied as well as the interplate earthquakes, yet once in a while they strike with catastrophic effect. In 1811 and 1812, two earthquakes of magnitude larger than 8 had struck at New Madrid in Missouri. These earthquakes devastated the region, created a new lake and changed the course of the river Missouri. In a few months, we reach the 200th anniversary of this earthquake. What if such an earthquake happens now?
Ground Beneath Our Feet
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The New Madrid earthquake was the worst intraplate earthquake known so far. Intraplate earthquakes of such intensity are rare. Moreover, they occur at places where the earth’s crust is weak. The crust at central US, where New Madrid lies, is stretched thin by tectonic forces and thus not strong enough. Gujarat, another site of intraplate earthquake, also has a crust weakened by several now-quiescent faults.
Central India, on the other hand, has a high degree of bulge from flexure due to stress built up from the Himalayas. Recent studies have discovered this stress as much as 1,000 km south of the Himalayas. The 1993 Latur earthquake had happened at a region of stress. This earthquake, measuring 6.4, had shocked seismologists as they had never expected an earthquake to happen there. The lessons of the recent spate of intraplate earthquakes are clear. A large portion of India lies in hazardous zones, a fact that is relevant to rapidly expanding nuclear power industry in India.
Given the ability of intraplate earthquakes to surprise, one should expect damaging earthquakes at many places in the country. Even southern cities are not entirely safe, although seismologists do not expect even moderate earthquakes to happen there. Many high-rise buildings are built without following any codes. Especially vulnerable are those on stilts and those built on or near dried lakes. The city of Bangalore is full of such buildings. So are several other cities in the country. Are we inching towards one of our worst natural disasters?
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