A Workshop on Microzonation ©Interline Publishing, Bangalore Seismic Microzonation of Bangalore

In the present study an attempt has been made to study the seismic hazard analysis considering the local site effects and to develop microzonation maps for Bangalore. Seismic hazard analysis and microzonation of Bangalore is addressed in this study in three parts: In the first part, estimation of seismic hazard using seismotectonic and geological information. All the earthquake sources and seismicity has been considered within a radius of 350 km from the Bangalore city for the study. Second part deals about site characterization using geotechnical and shallow geophysical techniques. An area of about 220 sq.km encompassing Bangalore Municipal Corporation has been chosen as the study area. There were over 150 lakes, though most of them are dried up due to erosion and encroachments leaving only 64 at present in BMP (Bangalore Mahanagara Palika) area. emphasizing the need to study site effects. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis (using the program SHAKE 2000) using both borehole SPT data and shear wave velocity survey data within an area of BMP. Further, field experiments using microtremor studies have also been carried out (jointly with NGRI) for evaluation of predominant frequency of the soil columns. The same has been assessed using 1-D ground response analysis and compared with microtremor results. Further, Seed and Idriss’s simplified approach has been adopted to evaluate the liquefaction susceptibility and liquefaction resistance assessment. Microzonation maps have been prepared for Bangalore city covering 220 sq. km area on a scale of 1:20000. Key words: Seismic hazard, Microzonation, site characterization, shear wave velocity, site response and liquefactio