Earlier this month, Kolkata felt some mild tremors. The social media was flooded with updates. âHave we just been hit by an earthquake? Felt our apartment swaying for a few seconds,â Shyambazar resident, Rajrupa Ghosh posted on Facebook just minutes after the tremors.
âDid anyone else feel the shake today? We emptied our office buildings and scurried downâ Sanchit Saxena, a bank employee working in Dalhousie, tweeted later that day.
It was an earthquake measuring 3.6 on the Richter scale with its epicentre located at Uluberia in Howrah. Though there were no damages reported, this magnitude is categorised as âstrongâ nonetheless. The other one this year was in May measuring almost 4 on the Richter scale and with the epicentre in Bankura. Kolkata has been witnessing minor earthquakes quite often in the last few years. If something major like the one in Nepal 2015 does strike the city, how prepared are we to face it?
The Threat of a Severe Earthquake is Real
A recent study by IIT-Kharagpur from 2011 to 2015 has found that Kolkata is sitting on the soft soil of the alluvium kind. This essentially means that the metro is staring at severe risk of soil liquefaction that will give way easily in the face of strong earthquakes. The study undertaken under the aegis of the Ministry of Earth Sciences has compiled seismic hazard maps for both Kolkata and New Delhi. The findings of the research have been shared with the concerned state and union government authorities, and also published in the Journal of Seismology.
The nature of the soil in the south-eastern parts of the city including upcoming suburbs, old central areas have a high risk of liquefaction. In the presence of groundwater aquifers, wetlands in the east and the Hooghly in the west, the soft clay-sand-silt-decomposed vegetation soil combination of Kolkata when mixes with water loses its strength. The resultant fluid soil compromises the foundations of building structures thereby making them sink in the event of moderate to high tremors.
The IIT-Kharagpur study has investigated and identified the risks at 654 sites across the city using a geotechnical investigation called micro-zonation. This process is a step ahead from the mere classification of seismic risk. In fact, micro-zonation provides an assessment of hazard areas and ground movement estimates. Thus, it can facilitate pre-construction guidelines as well as post-construction protection activities.
The areas that are under severe to high risk of soil liquefaction are: Anandapur, Bagbazar, Baguiati, Bally, Ballygunge, Beleghata, Belur, Dasnagar, Dhakuria, Dhapa, Eden Gardens, Garia, Howrah, Jadavpur, Kalighat, Kasba, Maidan, Mansadingi, New Town, Park Circus, Park Street, Rajarhat, Salt Lake, Sanatanpur, Shyambazar, Sinthi, Sultanpur, Taratola, Teghoria and Tollygunge. There are still other areas in Kolkata which fall under the moderate to low risk index.
The Past as a Lesson
The last time the city faced a severe soil liquefaction threat triggered by an earthquake was in 1934 and it measured 8.1 on the Richter scale. According to the records in Memoirs of the Geological Survey of India, the epicentre was located in the Bihar-Nepal border and affected severe damages in Ballygunge, Metiabruz, Rabindra Sadan and Sovabazar areas.
But has the city learned from its past? The IIT-Kharagpur study has many inputs from the engineering and structural construction-related points if the regulatory agencies take up cudgels. They should rigorously follow the codes of structural engineering just as fire safety codes are seen through. Kolkata is a melange of construction periods ranging from the pre-British era, to the colonial monuments to modern ones and often the news of structural failure greets the citizens. In such circumstances, this study should not be relegated to an academic exercise but should be integrated into practice.
The Current State of Preparedness
The West Bengal Disaster Management Department has crisis management arrangements during natural calamities and also prepares plans under disaster management for all tiers of the state authorities but still does not have substantial or consolidated codes for the prevention of large-scale damages.
The government needs to strengthen the network of regulatory authorities looking into the techno-legal regime of new and existing constructions. There should be a dedicated review of building bylaws, zonal code provisions and certification of architects and engineers.
On the level of local civic bodies, there should be a strong institutional framework that both supervises and regulates builders, promoters and real estate developers to adhere to safety norms in construction. The rampant neglect of laws in safe building procedures should be checked at this stage.
On their part, the citizens can also contribute to disaster preparedness by generating awareness and by dispensing responsible upkeep. The existing constructional retrofitting of buildings should be pursued with zeal with building contractors. The city has over 2500 unsafe buildings, mostly across central and north Kolkata, which could suffer heavy damages or even collapse during the monsoon spells itself. Imagine the tragedy waiting to happen in the face of severe earthquake!
The Way Ahead
Earthquakes are not just a hazard for houses but to bridges, electricity channels, gas lines, roads, telecommunications, and other essential infrastructures. The government should initiate earthquake preparedness plans from the ground up starting from Nagarik Samitis to generate awareness and work towards urban resilience. There should be careful and strict regulation of building activities wherein all earthquake-proof infrastructure investments are made.
Also, residentâs associations should be aware of all required codes of provisions and retrofitting measures in aging infrastructures and work in tandem with local authorities to institute all adaptation measures.
Local civic bodies should take preparedness in the real sense of the term by legislating for mandatory retrofitting, generating awareness through drills, setting response teams of volunteers and experts included. The sensitisation towards capacity building is strongly needed in urban and suburban development areas of Kolkata where the real estate boom is palpable.
The damage scenario in the face of a severe earthquake in Kolkata given the soil status and the proximity of the coast is immense and therefore, the onus of disaster management and preparedness is to be equally shared by the government at all levels and by the citizens. Decentralisation of hazard mapping, assessment and preparedness is the need of Kolkata now. If we donât wake up to these realities now, it could be too late.