Eco-Scope Bihar
When Nature strikes…human beings have no answer…
By Prof. Ashok Kumar Ghosh
I was working in my home (Third Floor) on my computer in the evening on 18th September, 2011 when suddenly the computer screen started shaking. My home has many rodents, and first I thought that it is mischief by some of them. I knocked the screen a few times and kept working. But the screen of computer continued its trembling, and then it came to my mind that it is not a mischief by rodents, but it is earthquake. I ran for my life downstairs shouting that it is earthquake. By the time I reached ground floor, it was gone, but almost all of my neighbours were on road. This was my third encounter with earthquake – the first was on 21st August, 1988 at Patna, the second was on 22nd December at San Diego, USA, and third on 18th September, 2011.All the three earthquakes were mild and by the grace of God the damage was very limited, but we do not know what the future has in store for us.
Based on the geo-tectonic features, history of past seismic events and potential hazards from earthquakes, the entire north-eastern and eastern region of India has been included in the severe seismic Zone V/IV of BIS code. At least a dozen mega earthquakes of more than 7 in the Richter scale had devastated the region during the past eleven and half decades and at least two of them – the great Shillong earthquake of 1897 and the Assam earthquake of 1950, both recorded 8.7 in the Richter scale, are considered among the most severe earthquakes anywhere in the world. The largest instrumented earthquake in Bihar was recorded on 15th January 1934 – Location was Bihar- Nepal border and the magnitude was 8.4 on Richter scale. Close to 10,700 people killed in North Bihar and Nepal. Heavy damage in the towns of Muzaffarpur, Motihari, Dharbhanga, and Munger was recorded. Tremors were felt all over the Indian subcontinent, as far as Mumbai and even Kerala.
Seismo-tectonic analysis of the eastern Himalayan zone has clearly indicated that many of the transverse strike-slip faults are at present active producing most of the earthquake events in this zone. The most important of them, from west to east, are East Patna, Kanchen Dzonga, Yadaon Gulu, Tista, Jamuna, Dudhnoi, Kulsi, Gyau , Kopili and Bomdila faults . Focal mechanism solutions for well constrained events occurring along these faults yielded predominantly strike-solutions but the events occurring along the central Himalayan graben structures gave normal solutions. It may be mentioned here that the Dudhnoi and Kulsi faults cutting across the Meghalaya Plateau and Brahmaputra valley also traverse across the frontal Himalayan fold and thrusts belt.
The state of Bihar lies in the Gangetic Plain. This is a fore-deep, a down warp of the Himalayan foreland, of variable depth, converted into flat plains by long-vigorous sedimentation. This is known as a geosyncline and the Gangetic Plain is the Indo-Gangetic Geosyncline. This has shown considerable amounts of flexure and dislocation at the northern end and is bounded on the north by the Himalayan Frontal Thrust.
The September 18, 2011 Sikkim, India earthquake occurred near the boundary between the India and Eurasia plates, in the mountainous region of northeast India near the Nepalese border. Initial analysis suggests the earthquake was complex, likely a result of two events occurring close together in time at depths of approximately 20 km beneath the Earth’s surface.
At the latitude of the September 18 earthquake, the India plate converges with Eurasia at a rate of approximately 46 mm/year towards the north-northeast. The broad convergence between these two plates has resulted in the uplift of the Himalayas, the world’s tallest mountain range. The preliminary focal mechanism of the earthquake suggests strike slip faulting, and thus an intraplate source within the upper Eurasian plate or the underlying India plate, rather than occurring on the thrust interface plate boundary between the two. This region has experienced relatively moderate seismicity in the past, with 18 earthquakes of M 5 or greater over the past 35 years within 100 km of the epicenter of the September 18 event.
The impact of this earthquake in Bihar was mild, but it should be taken as warning by nature for future. Earthquake in Bihar came as a nature’s warning and raised question mark over the congested urban planning. The buildings of all the cities of Bihar are not built to face the fury of major earthquake. If in future the earthquake of M6 or greater may be devastating for all the cities of Bihar, including Patna. Construction of multi-storey buildings in congested urban locality, which don’t comply with the conditions of earthquake resistant construction, should be completely prohibited.
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Prof. Ashok Kumar Ghosh is Professor-in-Charge in the department of Environment and Water Management, A.N.College [Magadh University], Patna, India.He writes a column on environment and water resources in Bihar, exclusively for BiharDays every Mondays.
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