Earthquake in India

[Guest]

[url="http://dailypioneer.com/pioneer-news/top-story/8961-when-the-earth-pushed-west.html"]When the earth pushed west[/url]

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.