Site Characterization and Seismic Vulnerability Studies of greater Shillong Meghalaya
The seismic vulnerability of highly populated cities can be accessed through quantification of site amplification behaviour, seeking intensity and the resonance pattern of ground vibration and their impact on built environment lifeline structures and the population as a whole. The site response parameters can be used to identify the area if higher amplification based on surface geology and may be correlated to the natural frequency of the sun. The mapping of the soil behaviour in general provides an over view of the possible damage of an individual structure or a set of buildings. During the recent years the State Capitals of the North East India have experience a burgeoning growth of population and commercialization. The entire North East India lies in the seismically vulnerable zone V as displayed in the seismic zoning map of India. Moreover, the reason is structurally very complex and has experience 2 great earthquake past in 1897 and 1950. Keeping view of the active seismic history, the necessity to adopt seismic micro zoning procedure for the thickly populated cities and urban areas of North East India imperative.
Keeping in mind council of scientific and industrial research (CSIR) North East Institute of Science & Technology (NEIST), Jorhat and department of Revenue & Disaster Management, Government of Meghalaya has jointly proposed to conduct and study on site characterization and seismic vulnerability study for greater Shillong. Total project cost of the study is ` 70.05 Lakhs out of which CSIR-NEIST, Jorhat contributed 50.25 Lakhs and remaining 19.80 Lakhs will be beared by Revenue & Disaster Management, Government of Meghalaya. The Project duration is of 2 years. The implementing agency will be CSIR-NEIST, Jorhat and Co-ordinating agency is Department of Revenue & Disaster Management, Government of Meghalaya.
The main objectives of the proposed study can be summarized as –
- Preparation of base map and thematic maps such as geology and geomorphology, lithology, soil and works type, seismicity and seism tectonics, ground water and hydrogeology, land use/land cover, forest cover ,habit and habitat and population density using remote sensing and GIS tool.
- Preparation of seism tectonics map covering 305-500Km radius of Shillong city and using local/global seismic network data, identification of active tectonic lineament.
- Geotechnical investigation, SPT borehole and n value up to 30m depth from available borehole data covering geographical and geological variation for determination of spatial variation for shear wave velocity using empherical relations which will lead to identification of liquefaction potential.
- Determination of predominant frequency as well representated sites from the ratio between Fourier spectra of horizontal and vertical component of noise survey.
- Integration of data liquefaction, susceptibility, local geology, hydrogeology, seismicity and seism tectonic, geotechnical data with local seismic site amplification and land use pattern geographical information system (GIS) to generate seismic site amplification map for Shillong.
- An area of 250sq km covering Shillong City and is suburb is proposed to map (site amplification, ground acceleration and basement contour) on a to neighbourhood basis. Important land form, topographic features and manmade structures identified through field traversing and using satellite imageries with geo coded and plotted on the basement
- Compilation of geological/geomorphologic map of city showing varies land form, rock types and geomorphic features on 1:2 25,000 maps.
- The corresponding grid points selected on the topographic map/base map will be identify in the field with the help of hand held GPS.
- Total 150 stations/sampling points (preferable at 0.5 to 1km grid interval) will be considered for site amplification and basement contour map.
- Data acquisition for site amplification (continuous modes/100sps) will be completed within 4-6 month by deploying as many as 4-5 sets of weak motion seismographics.