When the earth pushed west
25 September 2011
The Sikkim earthquake has thrown both a challenge and an opportunity. UTPAL KUMAR, however, is not too sure if we will go for the right option
It was one calamitous September morning that changed Japan forever. On September 1, 1923, a massive earthquake shook that country’s Kanto Plain, killing at least 100,000 people and reducing the entire region to rubble. The devastation was so absolute, and the loss so mind-boggling, that Japan, for a moment, considered shifting its capital out of Tokyo. Thankfully, better sense prevailed and the people decided to fight it out — first by replacing fire-prone, wood and brick buildings with concrete and steel towers. And, then, by regularly updating their building guidelines and advancing research on earthquake safety and disaster management. Ninety years on, Japan continues to tremble, but it rarely witnesses a trail of death and destruction on the scale it encountered on that fateful September morning. Even in March this year, when the country was hit by an 8.9 magnitude earthquake, people suffered not because of tremors but due to accompanying tsunami that hit the Japanese shores with a vengeance.
India, too, encountered its ‘September moment’ last Sunday — in Sikkim and its suburbs. In magnitude and scale of destruction, this might not be a landmark earthquake, but it has done something that is likely to challenge the authorities to re-assess the country’s hazard zones.
So far, it has been known that India’s landmass is inching slowly up, moving in the north and north-easterly direction. The interaction of this moving landmass with the Eurasian tectonic plate — one getting below the other — in the Himalayas is what causes most of the tremors in the region. The September 18 earthquake, however, was not the result of a forward pushing of the Indian plate; it was caused by lateral movements.
“The initial analysis of the Sikkim earthquake suggests that it wasn’t caused by one plate thrusting beneath another, but by so-called ‘strike-slip faulting’, a mechanism where fault systems slide side-to-side when two tectonic plates butt heads. Geologists suspect that the earthquake was due to an intra-plate fault within the upper Eurasian plate or the underlying Indian plate, rather than the interface between the two plates,” says Prof RB Singh of the Department of Geography, Delhi School of Economics.
HR Wason, Head of the Department of Earthquake Engineering at IIT Roorkee, is surprised to see the lateral movement in the region. “Such movements are not known to happen in the Himalayas,” says he. Prof Paul Segall of Stanford University, however, believes there’s nothing new in all this. “It is not atypical to have diverse types of fault movement even in an area dominated by convergence of two plates,” he says. Roger G Bilham of Colorado University takes Segall’s argument forward, when he says: “The slip in this earthquake is an indication of ‘differential’ northward motion of the Indian plate and possibly the subsequent adjustment of the Tibetan Plateau above it.”
But, do all these make the region more vulnerable to earthquakes?
“Intra-plate earthquakes do not occur near plate boundaries, but at the location of ancient failed rifts, because such old structures may present a weakness in the crust where it can easily slip to accommodate regional tectonic strain. The earthquake caused by sideways movement of plates, therefore, is generally located in the stable interior parts of continents which are believed to be less vulnerable to hazards,” says Singh.
The recent event of intra-plate earthquake in Sikkim has, thus, pushed the hazard line to further south of the Himalayas. “I believe the Sikkim quake should serve as a reminder that more parts of the region than actually thought of are prone to earthquakes and planning should account for this risk,” says Segall.
Currently, as far as earthquakes are concerned, the country has been divided into five zones. The Northeast, Jammu & Kashmir, and a significant portion of Himachal Pradesh and Uttarakhand come under Zone V, which is the most volatile of the earth’s seismic centres. Uttar Pradesh, Delhi and a part of Uttarakhand fall in Zone IV. Central India is bracketed under Zone III; and, south India comes under Zone II. Now, after the Sikkim tremor, the entire zone system has to be reorganised, and the threat perception recast.
source; The daily pioneer
Heightened seismic activity
There are seismologists who believe that the earth has experienced a noticeable increase in seismic activity and intensity over the past few years. According to latest statistics from the United States Geological Survey, between 1986 and 1996, there were 15 earthquakes of magnitude 7.0 or greater. In the next 10 years, the frequency increased by more than six times. Even the rate of lesser magnitude earthquakes has increased. Around 120 earthquakes of magnitude 6.0-6.9 take place every year. And, in the last week alone, we have had six. At this rate, we would end up having almost three-times more earthquakes this year!
“I don’t think anyone can explain why the activity has increased,” says Segall. Several theories have been put forth to explain what is happening. Though most of them are no better than conspiracy theories, a few seem credible. One of the theories has to do with a meteor that has returned to the earth’s proximity and may be affecting its gravity balance. Another theory points to solar flares reaching the earth’s surface, thus affecting its electro-magnetic fields. And, of course, there are some who believe that the earth’s rotational axis has shifted, causing changes in climate, waves and gravity; this, according to them, has resulted in hurricanes, earthquakes and tornadoes.
Bilham, though not certain about the reasons behind heightened seismic activity in recent times, says there is nothing strange in all this. “It is not unusual for earthquakes to appear more frequently. They occur rather randomly and hence some periods of time will seem to contain more than others,” he says.
RK Chadha, Chief Scientist, CSIR-National Geophysical Research Institute, Hyderabad, agrees with Bilham. “The last 100 years of global data show that during the 1940-50 decade the earth was seismically more active. Since 2000, we have been again witnessing a seismically active period, more so after the 9.1 magnitude earthquake in Sumatra (2004). ‘Why’, is the million dollar question at the moment and is the area of active research globally,” he says.
Prepare for the worst
At least 38 Indian cities, including Delhi, Mumbai, Kolkata, Chennai and Ahmedabad, fall within moderate-to-high risk seismic zones. And, if reports are to be believed, India must prepare itself for earthquakes of Japan-like frequency and intensity, if not more. “The northern part of the subcontinent has long been awaiting an earthquake of magnitude 9,” says an Indian Meteorological Department official on the condition of anonymity. Jean-Philippe Avouac, a geophysicist at the California Institute of Technology, too, believes that an earthquake of high magnitude — like the one witnessed in Japan — is overdue. “The Himalayan region has a lot of energy that needs to be released at some point,” he says.
Earthquakes in the Himalayas can go beyond magnitude eight. “There have been four earthquakes over magnitude eight — 1897 Shillong, 1905 Kangra, 1934 Bihar-Nepal border and 1950 Arunachal Pradesh. So, the occurrence of a large magnitude earthquake cannot be ruled out,” says Chadha.
Such large earthquakes can occur either on thrust faults or strike-slip. So, the implications of earthquake hazard in the Himalayan region will not change. But, as the Sikkim quake has revealed, a large number of cities located in the vicinity of the Himalayas are no less vulnerable. “Earthquake hazards depend on the local site conditions in which you are located. It will increase in the presence of thick pile of sediments where seismic waves are amplified, causing more damage. This can happen even up to the distance of 300-400 km. Hence, several cities in the Indo-Gangetic plains where the thickness of sediments varies between 500 metres and 6,000 metres are exposed to earthquakes. The 2001 Bhuj earthquake in Gujarat is a perfect example as the tremors led to the collapse of buildings in Ahmedabad, located more than 300 km from the epicentre; in 1985, Mexico City suffered heavy damage due to an earthquake whose epicentre was along the coast in the Pacific Ocean, located more than 300 km away from the Mexican capital,” says Prof Chadha.
Quakes not real killers
“In recent earthquakes, buildings have acted as weapons of mass destruction,” remarked a leading seismologist after the devastating earthquake hit the Caribbean island of Haiti in January 2010, killing more than 300,000 people. Poor quality construction on the island made the quake lethal. The 8.8-magnitude earthquake that hit Chile a month later was 500-times stronger than the Haiti one. And, yet, the number of casualties in Chile was exponentially smaller, with the official death toll being confined to a few hundreds.
India is no different from Haiti. The Sikkim earthquake should, therefore, be a wake-up call for all concerned — the Government, policymakers and law enforcers. An earthquake on the scale that Japan or Chile experienced would lay waste whole cities here. But before the authorities can do anything, they need to understand that quakes do not kill people, buildings do. Safety essentially lies in ensuring quake-resistant construction of buildings. This is where our real worry lies, as illegal and poor quality constructions continue to be the bane of urban India, coupled with a lack of awareness of safety norms.
Bilham believes India is not being pro-active enough in dealing with earthquake hazards. “Building codes exist and need to be implemented, not avoided by corrupt or ignorant contractors,” the Colorado University professor says.
“Large earthquakes today will have greater impact because of haphazard way of urbanisation taking place in the country and also the density of population in large cities. Mushrooming of multi-storied buildings, especially in the hilly regions of the Himalayas, is equally worrisome,” says Chadha.
Traditional houses of wood and stone survived the Uttarkashi earthquake in 1991. One cannot prevent earthquakes from happening, but one can definitely construct a building that doesn’t pose danger when disasters strike. Perhaps the damage in the Sikkim quake could have been minimal, had authorities learnt lessons from Uttarkashi and discouraged the construction of ‘modern’ buildings in the mountains.
Also, the Government should understand that the seismic process in Sikkim and its suburbs has been complicated by the presence of multiple dams on the Teesta river and its tributaries. Though the role of the dams in the recent tremor is yet to be studied, the earthquake could have a Teesta angle. After all, in 1970, a major earthquake in Maharashtra was triggered by the Koyna dam located on the Sahyadri Hills. The Government needs to tread carefully on the issue as its “master vision” identifies the Northeast as the country’s “future powerhouse” by building about 168 dams in the region.
So, last Sunday a choice was given to us: To choose the Japanese way of tackling earthquakes, or go down the Haitian way. The choice is ours. The Sikkim quake has only emphasised that the threat is greater than what we actually believed.
25 September 2011
The Sikkim earthquake has thrown both a challenge and an opportunity. UTPAL KUMAR, however, is not too sure if we will go for the right option
It was one calamitous September morning that changed Japan forever. On September 1, 1923, a massive earthquake shook that country’s Kanto Plain, killing at least 100,000 people and reducing the entire region to rubble. The devastation was so absolute, and the loss so mind-boggling, that Japan, for a moment, considered shifting its capital out of Tokyo. Thankfully, better sense prevailed and the people decided to fight it out — first by replacing fire-prone, wood and brick buildings with concrete and steel towers. And, then, by regularly updating their building guidelines and advancing research on earthquake safety and disaster management. Ninety years on, Japan continues to tremble, but it rarely witnesses a trail of death and destruction on the scale it encountered on that fateful September morning. Even in March this year, when the country was hit by an 8.9 magnitude earthquake, people suffered not because of tremors but due to accompanying tsunami that hit the Japanese shores with a vengeance.
India, too, encountered its ‘September moment’ last Sunday — in Sikkim and its suburbs. In magnitude and scale of destruction, this might not be a landmark earthquake, but it has done something that is likely to challenge the authorities to re-assess the country’s hazard zones.
So far, it has been known that India’s landmass is inching slowly up, moving in the north and north-easterly direction. The interaction of this moving landmass with the Eurasian tectonic plate — one getting below the other — in the Himalayas is what causes most of the tremors in the region. The September 18 earthquake, however, was not the result of a forward pushing of the Indian plate; it was caused by lateral movements.
“The initial analysis of the Sikkim earthquake suggests that it wasn’t caused by one plate thrusting beneath another, but by so-called ‘strike-slip faulting’, a mechanism where fault systems slide side-to-side when two tectonic plates butt heads. Geologists suspect that the earthquake was due to an intra-plate fault within the upper Eurasian plate or the underlying Indian plate, rather than the interface between the two plates,” says Prof RB Singh of the Department of Geography, Delhi School of Economics.
HR Wason, Head of the Department of Earthquake Engineering at IIT Roorkee, is surprised to see the lateral movement in the region. “Such movements are not known to happen in the Himalayas,” says he. Prof Paul Segall of Stanford University, however, believes there’s nothing new in all this. “It is not atypical to have diverse types of fault movement even in an area dominated by convergence of two plates,” he says. Roger G Bilham of Colorado University takes Segall’s argument forward, when he says: “The slip in this earthquake is an indication of ‘differential’ northward motion of the Indian plate and possibly the subsequent adjustment of the Tibetan Plateau above it.”
But, do all these make the region more vulnerable to earthquakes?
“Intra-plate earthquakes do not occur near plate boundaries, but at the location of ancient failed rifts, because such old structures may present a weakness in the crust where it can easily slip to accommodate regional tectonic strain. The earthquake caused by sideways movement of plates, therefore, is generally located in the stable interior parts of continents which are believed to be less vulnerable to hazards,” says Singh.
The recent event of intra-plate earthquake in Sikkim has, thus, pushed the hazard line to further south of the Himalayas. “I believe the Sikkim quake should serve as a reminder that more parts of the region than actually thought of are prone to earthquakes and planning should account for this risk,” says Segall.
Currently, as far as earthquakes are concerned, the country has been divided into five zones. The Northeast, Jammu & Kashmir, and a significant portion of Himachal Pradesh and Uttarakhand come under Zone V, which is the most volatile of the earth’s seismic centres. Uttar Pradesh, Delhi and a part of Uttarakhand fall in Zone IV. Central India is bracketed under Zone III; and, south India comes under Zone II. Now, after the Sikkim tremor, the entire zone system has to be reorganised, and the threat perception recast.
source; The daily pioneer
Heightened seismic activity
There are seismologists who believe that the earth has experienced a noticeable increase in seismic activity and intensity over the past few years. According to latest statistics from the United States Geological Survey, between 1986 and 1996, there were 15 earthquakes of magnitude 7.0 or greater. In the next 10 years, the frequency increased by more than six times. Even the rate of lesser magnitude earthquakes has increased. Around 120 earthquakes of magnitude 6.0-6.9 take place every year. And, in the last week alone, we have had six. At this rate, we would end up having almost three-times more earthquakes this year!
“I don’t think anyone can explain why the activity has increased,” says Segall. Several theories have been put forth to explain what is happening. Though most of them are no better than conspiracy theories, a few seem credible. One of the theories has to do with a meteor that has returned to the earth’s proximity and may be affecting its gravity balance. Another theory points to solar flares reaching the earth’s surface, thus affecting its electro-magnetic fields. And, of course, there are some who believe that the earth’s rotational axis has shifted, causing changes in climate, waves and gravity; this, according to them, has resulted in hurricanes, earthquakes and tornadoes.
Bilham, though not certain about the reasons behind heightened seismic activity in recent times, says there is nothing strange in all this. “It is not unusual for earthquakes to appear more frequently. They occur rather randomly and hence some periods of time will seem to contain more than others,” he says.
RK Chadha, Chief Scientist, CSIR-National Geophysical Research Institute, Hyderabad, agrees with Bilham. “The last 100 years of global data show that during the 1940-50 decade the earth was seismically more active. Since 2000, we have been again witnessing a seismically active period, more so after the 9.1 magnitude earthquake in Sumatra (2004). ‘Why’, is the million dollar question at the moment and is the area of active research globally,” he says.
Prepare for the worst
At least 38 Indian cities, including Delhi, Mumbai, Kolkata, Chennai and Ahmedabad, fall within moderate-to-high risk seismic zones. And, if reports are to be believed, India must prepare itself for earthquakes of Japan-like frequency and intensity, if not more. “The northern part of the subcontinent has long been awaiting an earthquake of magnitude 9,” says an Indian Meteorological Department official on the condition of anonymity. Jean-Philippe Avouac, a geophysicist at the California Institute of Technology, too, believes that an earthquake of high magnitude — like the one witnessed in Japan — is overdue. “The Himalayan region has a lot of energy that needs to be released at some point,” he says.
Earthquakes in the Himalayas can go beyond magnitude eight. “There have been four earthquakes over magnitude eight — 1897 Shillong, 1905 Kangra, 1934 Bihar-Nepal border and 1950 Arunachal Pradesh. So, the occurrence of a large magnitude earthquake cannot be ruled out,” says Chadha.
Such large earthquakes can occur either on thrust faults or strike-slip. So, the implications of earthquake hazard in the Himalayan region will not change. But, as the Sikkim quake has revealed, a large number of cities located in the vicinity of the Himalayas are no less vulnerable. “Earthquake hazards depend on the local site conditions in which you are located. It will increase in the presence of thick pile of sediments where seismic waves are amplified, causing more damage. This can happen even up to the distance of 300-400 km. Hence, several cities in the Indo-Gangetic plains where the thickness of sediments varies between 500 metres and 6,000 metres are exposed to earthquakes. The 2001 Bhuj earthquake in Gujarat is a perfect example as the tremors led to the collapse of buildings in Ahmedabad, located more than 300 km from the epicentre; in 1985, Mexico City suffered heavy damage due to an earthquake whose epicentre was along the coast in the Pacific Ocean, located more than 300 km away from the Mexican capital,” says Prof Chadha.
Quakes not real killers
“In recent earthquakes, buildings have acted as weapons of mass destruction,” remarked a leading seismologist after the devastating earthquake hit the Caribbean island of Haiti in January 2010, killing more than 300,000 people. Poor quality construction on the island made the quake lethal. The 8.8-magnitude earthquake that hit Chile a month later was 500-times stronger than the Haiti one. And, yet, the number of casualties in Chile was exponentially smaller, with the official death toll being confined to a few hundreds.
India is no different from Haiti. The Sikkim earthquake should, therefore, be a wake-up call for all concerned — the Government, policymakers and law enforcers. An earthquake on the scale that Japan or Chile experienced would lay waste whole cities here. But before the authorities can do anything, they need to understand that quakes do not kill people, buildings do. Safety essentially lies in ensuring quake-resistant construction of buildings. This is where our real worry lies, as illegal and poor quality constructions continue to be the bane of urban India, coupled with a lack of awareness of safety norms.
Bilham believes India is not being pro-active enough in dealing with earthquake hazards. “Building codes exist and need to be implemented, not avoided by corrupt or ignorant contractors,” the Colorado University professor says.
“Large earthquakes today will have greater impact because of haphazard way of urbanisation taking place in the country and also the density of population in large cities. Mushrooming of multi-storied buildings, especially in the hilly regions of the Himalayas, is equally worrisome,” says Chadha.
Traditional houses of wood and stone survived the Uttarkashi earthquake in 1991. One cannot prevent earthquakes from happening, but one can definitely construct a building that doesn’t pose danger when disasters strike. Perhaps the damage in the Sikkim quake could have been minimal, had authorities learnt lessons from Uttarkashi and discouraged the construction of ‘modern’ buildings in the mountains.
Also, the Government should understand that the seismic process in Sikkim and its suburbs has been complicated by the presence of multiple dams on the Teesta river and its tributaries. Though the role of the dams in the recent tremor is yet to be studied, the earthquake could have a Teesta angle. After all, in 1970, a major earthquake in Maharashtra was triggered by the Koyna dam located on the Sahyadri Hills. The Government needs to tread carefully on the issue as its “master vision” identifies the Northeast as the country’s “future powerhouse” by building about 168 dams in the region.
So, last Sunday a choice was given to us: To choose the Japanese way of tackling earthquakes, or go down the Haitian way. The choice is ours. The Sikkim quake has only emphasised that the threat is greater than what we actually believed.
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