Seismic vulnerability assessment of Gangtok city and its mitigation measures

Abstract

Natural disasters are one of the most severely feared natural phenomena where the nature takes back control from anthropogenic developments and causes large scale destruction of properties and loss of human lives. Seismic disasters, primarily used as synonyms for earthquake, but technically also include associated events such as landslides are one of the most common disasters faced by society today. Any area which due to its locations, faces large number of seismic activity and its ill-prepared to face its impact, is term to be seismically vulnerable area. Gangtok, capital of state of Sikkim, is located at the altitude of 1650 meters in the Himalayan ranges in NorthEastern part of India. It had population of 98000 in 2011 and is spread over the area of 19 square KM. Due to inherent geological instability of Himalayan ranges, the area faces an at least one earthquake with intensity greater than 5 on Richter scale. This thesis studies the variations in vulnerability between the different wards of the Gangtok city due to various parameters. Although much of the past efforts in the domain of seismic disaster have been reactive in nature, a change in paradigm with focus on reducing the vulnerability to earthquake has taken spotlight. Various man made aspects of city such as building material, open spaces, critical services, etc. have influence on the impact of seismic disaster. This thesis also studies such parameters to understand variations in seismic vulnerability within the city boundary. Various analysis employing advance GIS and remote sensing techniques such as NDBI, service area determination, Thiessen polygon formulation, etc. have been used throughout this thesis. Based upon these parameters, vulnerability of every ward of the city, including the reasons for the given level of vulnerability is determined. For those wards which are identified to have high seismic vulnerability, proposals based upon their development status have been given. Suitable suggestions have been given to divert future urban growth from vulnerable to safer wards along with methods to reduce vulnerability of already developed wards. The thesis concluded with suggestion for further research required for effective integration of these suggestions in development / master plan of city.