Seismotectonic Map

Seismotectonic map showing the geology, geomorphology, water features, faults, lineaments, shear zone and past earthquake events has been prepared for Bangalore. Seismicity of an area is the basic issue to be examined in seismic hazard analysis for evaluating seismic risk for the purpose of microzonation planning of urban centers. Detailed knowledge of active faults and lineaments and associated seismicity is required to quantify seismic hazard and risk. Indian peninsular shield, which was once considered to be seismically stable, has shown that it is quite active. Seismotectonic details of study area have been collected in a circular area having about 350 km radius around Bangalore. Study area lies between latitudes 9.83 north to 17.20 north and longitudes 74.4 east to 81.7 east.

Seismic Sources

 Seismotectonic details includes geology, rock type, fault orientation with length, lineaments with lengths, shear zones with length and seismic earthquake events. The well defined and documented seismic sources are published in the Seismotectonic Atlas-2000 published by Geological Survey of India. Geological survey of India has compiled all the available geological, geophysical and seismological data for thee entire India and has published a seismotectonic map in 2000. Seismotectonic atlas (SEISAT, 2000) contains 43 maps in 42 sheets of 3ox4o sizes with scale of 1:1 million, which also describes the tectonic frame work and seismicity. SEISAT is prepared with intention that it can be used for the seismic hazard analysis of Indian cities. In this analysis about 6 SEISAT maps are merged, seismic sources with 350km in a circular area having radius around Bangalore are used. Seismicity and activity of the plate tectonic will always change based on neotectonic activity of the region. Thus it is necessary that any seismic hazard should include recent seismicity. An extensive literature has been carried out to collect seismic sources from recent publications. Ganesha Raj and Nijagunappa (2004) have mapped major lineaments of Karnataka State with length more than 100 km using satellite remote sensing data and correlated with the earthquake occurrences. They have highlighted that there are 43 major lineaments and 33 earthquake occurrences with magnitude above 3 (since 1828) in the State. About 23 of these earthquakes were associated with 8 major lineaments, which they have named as active lineaments. The Mandya-Channapatna-Bangalore lineament, Lakshman Thirtha-KRS-Bangalore lineament, and Chelur-Kolar-Battipalle lineament are some of the seismically active lineaments identified by the authors. They have also stated that earthquakes are confined to the southern part of the state indicating that south Karnataka is seismically more active. The authors have also recommended the need to upgrade the seismic zonation map of Karnataka especially for areas surrounding Mandya, Bangalore, and Kolar. Karnataka lineaments published by Ganesha Raj and Nijagunappa (2004) using remote sensing data are also considered in the present study.

Seismicity of the Study Area

Seismic data collected from various agencies [United State Geological Survey (USGS), Indian Metrological Department (IMD), NewDelhi; Geological Survey of India (GSI) and Amateur Seismic Centre (ASC), National Geophysical Research Institute (NGRI),Hyderabad; Centre for Earth Science Studies (CESS), Akkulam, Kerala and Gauribindanur (GB) Seismic station] contain information about the earthquake size in different scales such as intensity, local magnitude or Richter magnitude and body wave magnitudes. These magnitudes are converted to moment magnitudes (Mw) to achieve the status of the uniform magnitude by using magnitude relations given by Heaton et al (1986). The data set contains 394 events which are less than moment magnitude 3, 790 events from 3 to 3.9, 212 events from 4 to 4.9, 22 events from 5 to 5.9 and 3 events which are more than moment magnitude 6.

The sources identified from SEISAT (2000) and remote sensing studies are compiled and a map has been prepared using Adobe Illustrator version 9.0. The seismotectonic map contains 65 numbers of faults with length varying from 9.73 km to 323.5km, 34 lineaments and 14 shear zones. The earthquake events collated and converted has been super imposed on base map with available latitudes and longitudes. The earthquake events collated are about 1421 with minimum moment magnitude of 1.0 and a maximum of 6.2 and earthquake magnitudes are shown as symbols with different shape and colours. Maximum source magnitude is assigned based on the maximum size of the earthquake close to the each of the sources.

Department of Civil Engineering

Indian Institute of Science, Bangalore

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Dr P Anbazhagan

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Department of Civil Engg

Indian Institute of Science

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This page was last updated on August 25, 2011