GIS BASED SEISMIC MICROZONATION OF WESTERN PART OF AHMEDABAD CITY

Abstract

Seismic microzonation is an engineering approach to analyze the detrimental effects of an earthquake on the soil and the structure constructed over it. It utilizes the services of persons from a variety of disciplines in the area of microzonation. It is useful in providing disaster mitigation measures for people in occurrence of an earthquake. The Kutchchh earthquake of 26 Jan.2001 caused wide spread damage in the city of Ahmedabad. A number of buildings collapsed that caused casualties. Some evidences of liquefaction were also reported in media. It might be a reason for the damage of buildings. The Seismic microzonation of Ahmedabad city is attempted on the basis of data made available by the Ahmedabad Municipal Corporation. This work is one of the pioneering works in India for microzonation of major urban and industrial centers. In the present study, the analysis has been carried out to find out the shear wave velocity, compression wave velocity, Young's modulus and dynamic shear modulus at various depths at different bore holes in Ahmedabad city. Shear wave velocity is computed on the basis of N-values that have been corrected for over burden pressure using codal provisions. After getting correct N-values, the plot given by Okamoto (1973), has been used to find out the shear wave velocity. Peak ground acceleration at different sites has been calculated after calculating magnification factor using equation suggested by Kanai (1962). After calculating the above mentioned parameters, the seismic microzonation maps have been prepared using software package SURFER. It is concluded from the seismic microzonation maps that the sites with higher velocities of shear waves and elastic moduli are safer than the sites of lower value of elastic moduli and wave velocities. Localities closer to the river have more chances of get damaged during an earthquake. The sites situated on filled up land are also weaker points and construction involves a lot of risk. Damage is more in southern parts of West Ahmedabad due to proximity to river and also due to presence of lower grounds and filled e l mod• Seismic microzonation is a comprehensive process. It needs thorough and elaborate research to complete it. In a small period of six months, it has been possible to deal with only a few parameters. A comprehensive work in this regard requires a lot more scientific data and efforts of technical personnel. The present work is a preliminary work in this ill direction which paves the way for further studies on larger scale with more organized efforts. iv