Nepal-like earthquake can sink Kolkata:Study

Drimi Chaudhuri, Kolkata, July 19, 2015, dhns:

The recent Nepal earthquake might have shaken Kolkata, but if experts are to be believed, a similar quake here could sink large parts of the city.

Several parts of the eastern metropolis sits on very soft alluvial soil and a major earthquake could lead the city to sink several inches.

The revelation was made in a report by IIT-Kharagpur in a study funded by the Union Ministry of Earth Sciences that lasted over four years. The premier technology institute, which has been studying Kolkata’s stability, revealed in a report released in June that given the soft alluvium kind of soil large parts of the city rests on, places like Park Street in central Kolkata, the central business district of Dalhousie, the satellite township of Salt lake in eastern Kolkata and the newly-developed Rajarhat New Town township could sink. While most of these areas are densely populated, researchers and scientists feel the situation is a disaster in waiting.

Even areas in the south-eastern fringe of the city along the arterial Eastern Metropolitan Bypass, which passes by the eastern, south-eastern and southern parts of Kolkata, connecting the airport to the city’s southern fringes, are faced with a similar fate.

What has got researchers worried is that most of these parts are witnessing a real estate boom, which is adding further pressure to the soil. These parts and several other pockets in the city are floating on a bed of slurry and could just sink in case a major earthquake strikes Kolkata.The study pointed out that this layer of slurry, composed sand, clay, silt and rotten vegetation, extends up to a depth of 7.5 km from the surface.

“In between there are ground water aquifers, many of which are shallow and located within one to seven metres from the surface. On the east there is the East Kolkata Wetlands and on the west flows the Hooghly. All these provide the water source that will contribute to the unstable nature of the region,” the study noted.

“A major earthquake measuring more than 6.5 on the Richter scale can lead to a phenomenon called liquefaction, a process by which soft soil mixes with water and temporarily loses its strength.

http://www.deccanherald.com/content/490257/nepal-like-earthquake-can-sink.html