Department of Civil Engineering

Indian Institute of Science, Bangalore

Seismic Microzonation of Bangalore


Bangalore has experienced several minor earthquakes in the 20th century. Even though damages caused by these earthquakes are not large, considering the rapid growth of the city coupled with indifferent planning has made Bangalore highly susceptible to earthquakes. Hence it is necessary to identify sub-regions within Bangalore (essence of microzonation) that may respond in a similar way to the earthquake. Prof T.G. Sitharam and Dr. P. Anbazhagan ,Civil Engineering Department Indian Institute of Science carried out extensive studies on seismic microzonation of Bangalore city, evaluated and mapped different hazard parameters for the project titled Seismic microzonation of Bangalore (Ref no. DST/23(315)/SU/2002 dated October 2003) funded by the Department of Science and Technology, Government of India . Part of research work is highlighted in IISc main web as How will different parts of Bangalore respond to an earthquake. This site presents the doctoral research work of Dr. P. Anbazhagan titled as SITE CHARACTERIZATION AND SEISMIC HAZARD ANALYSIS WITH LOCAL SITE EFFECTS FOR MICROZONATION OF BANGALORE in 2007.

In the present study an attempt has been made to characterize the site and to study the seismic hazard analysis considering the local site effects and to develop microzonation maps for Bangalore. Microzonation can be defined as the subdivision of a region into zones that have relatively similar exposure to various earthquake related effects. 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. Second part deals about site characterization using geotechnical and shallow geophysical techniques. An area of 220, encompassing Bangalore Municipal Corporation has been chosen as the study area in this part of the investigation. There were over 150 lakes, though most of them are dried up due to erosion and encroachments leaving only 64 at present in an area of 220 sq. km and 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 220 sq. km. 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 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.

The main objective of microzonation study is to effectively implement the selected parameters for land use and city planning. Therefore it is very important that the selected microzonation parameters should be meaningful for city planners as well as for public. Seismic zonation studies, whether they are at macro or micro scale are generally conducted by earth scientists (Seismologists or Geologist). But seismic microzonation requires an essential input from civil engineering, especially in the field of geotechnical engineering.