Posted by Dr. Gopal Unnikrishna Kurup
The Himalayan Earthquake
As of latest estimate, the Nepal earthquake death toll just exceeded 2400 with about 6000 injured. Since the main quake that measured 7.9 in Richter.Scale(RC), there have been over 60 aftershocks measuring over 4 to 6.7 RC. One solace is that compared to the last one that rocked Nepal in 1934 that measured 8.2 RC and claimed 10 to 12 thousand lives, this time the causalities so far are much smaller while not ruling out a steep rise in figures when more reports from interiors might pour in.
Nepal, located at the central part of the Himalaya represents one of the active seismic zones in the Himalaya There are historical indications that Kathmandu has been struck by repeated severe earthquakes in the past centuries, and more recently in last centuary we know at least 6 earthquakes have occurred in the country.
Earthquakes happen when any of the major six plates or many minor plates, of which the earth consists of, releases suddenly the pent up strain energy at their margins. Where today the Himalaya mountains exist there was an ancient sea called Tethys sea separating the Indian subdcontinent and Eurasian continent. Tethys was obliterated when the Indian plate underthrust the Eurasian continental plate raising a ridge between them as the rudiment of the Himalyas and raising it to the present height in a process of continued action of converging stress field in the last fifty-fi ve million years after the under thrust or collision commenced. The process is still ongoing although much dissipated, the indian plate moving at a rate of about 20 to 45 millimeters an year going under the Eurasian plate. resulting in potentail earthquakes. Pressure builds up as the plates push together, until the Indian plate lurches suddenly downwards, sending a great earthquake reverberating across hundreds of kilometres.
The Himalaya Mountains, now a well defined arc, and extending for ~2500 km from Nanga Parbat (8215 m) in west-northwest to Namcha Barwa (7755 m) to the east-northeast are therefore very much prone to earthquakes. Himalayan belt was rocked by four great earthquakes (1897 Assam, 1905 Kangra, 1934 Nepal-Bihar border and 1950 Assam) within fifty-five years (1897-1950) and large number of strong earthquakes caused huge loss of lives and property. Many regions of the central Himalayas are now holding onto at least four meters of convergence, which would cause a great earthquake when released. This amount of slip is thought to have occurred in the great earthquake of 1934 that rocked the Bihar-Nepal region.ut the pressure has been mounting,
Large earthquakes have struck this region every few decades since the early nineteenth century. Since 1950, when the biggest earthquake within a single continent in recorded history shook Assam, the fault lines have been silent. But the pressure has been mounting, and it was predicted since 2001 and as recent as a couple of months back that an earthquake of up to 8 RC was actually overdue. Considering probable ruptures of 150 km segments the Himalayan plate boundary at seven positions, Kashmir, DehraDun, Garhwal, West Nepal, Kathmandu, Bhutan and Assam are identified as places where sufficient elastic energy is believed to be accumulated for magnitude eight earthquakes. Even if the great thrusts of the Himalaya are now apparently quiescent for large earthquakes, the foothill shows geologically very recent faulting and thrusting on a large scale.
But unfortunately earthquakes cannot be predicted with the accuracy anywhere nearing that of climatic disasters like cyclones. We are rather helpless in preparing and be ready to mitigate the deadly effects. All that any country can do is to cope with its aftermath.
The Himalayan Earthquake
Nepal, located at the central part of the Himalaya represents one of the active seismic zones in the Himalaya There are historical indications that Kathmandu has been struck by repeated severe earthquakes in the past centuries, and more recently in last centuary we know at least 6 earthquakes have occurred in the country.
Earthquakes happen when any of the major six plates or many minor plates, of which the earth consists of, releases suddenly the pent up strain energy at their margins. Where today the Himalaya mountains exist there was an ancient sea called Tethys sea separating the Indian subdcontinent and Eurasian continent. Tethys was obliterated when the Indian plate underthrust the Eurasian continental plate raising a ridge between them as the rudiment of the Himalyas and raising it to the present height in a process of continued action of converging stress field in the last fifty-fi ve million years after the under thrust or collision commenced. The process is still ongoing although much dissipated, the indian plate moving at a rate of about 20 to 45 millimeters an year going under the Eurasian plate. resulting in potentail earthquakes. Pressure builds up as the plates push together, until the Indian plate lurches suddenly downwards, sending a great earthquake reverberating across hundreds of kilometres.
The Himalaya Mountains, now a well defined arc, and extending for ~2500 km from Nanga Parbat (8215 m) in west-northwest to Namcha Barwa (7755 m) to the east-northeast are therefore very much prone to earthquakes. Himalayan belt was rocked by four great earthquakes (1897 Assam, 1905 Kangra, 1934 Nepal-Bihar border and 1950 Assam) within fifty-five years (1897-1950) and large number of strong earthquakes caused huge loss of lives and property. Many regions of the central Himalayas are now holding onto at least four meters of convergence, which would cause a great earthquake when released. This amount of slip is thought to have occurred in the great earthquake of 1934 that rocked the Bihar-Nepal region.ut the pressure has been mounting,
Large earthquakes have struck this region every few decades since the early nineteenth century. Since 1950, when the biggest earthquake within a single continent in recorded history shook Assam, the fault lines have been silent. But the pressure has been mounting, and it was predicted since 2001 and as recent as a couple of months back that an earthquake of up to 8 RC was actually overdue. Considering probable ruptures of 150 km segments the Himalayan plate boundary at seven positions, Kashmir, DehraDun, Garhwal, West Nepal, Kathmandu, Bhutan and Assam are identified as places where sufficient elastic energy is believed to be accumulated for magnitude eight earthquakes. Even if the great thrusts of the Himalaya are now apparently quiescent for large earthquakes, the foothill shows geologically very recent faulting and thrusting on a large scale.
But unfortunately earthquakes cannot be predicted with the accuracy anywhere nearing that of climatic disasters like cyclones. We are rather helpless in preparing and be ready to mitigate the deadly effects. All that any country can do is to cope with its aftermath.
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