Article Preview
Top1. Introduction
The assessment of local site effect on strong ground motion characteristics plays an important role in earthquake engineering. If seismic wave travels from high velocity soil media to low velocity soil media, velocity decreases and amplitude of wave increases (Narayan, 2008; Zeng, 1996; Tsuda et al., 2006). Therefore identification of soft alluvial deposit susceptible to ground motion amplification plays an important role for purpose of seismic microzonation. The damage pattern during several past earthquakes like 1985 Mexico Earthquakes, 1989 San Franscisko Earthquake, 1995 Los Angeles Earthquake, 2001 Bhuj Earthquake (Kayen & Mitchell, 1997; Zeevaert, 1991; Seed et al., 1988; Dary et al., 2000; Narayan et al., 2002; Govindaraju et al., 2004) have shown that local site effect especially soft soil plays important role in ground motion amplification.
Kolkata City has experienced shaking due to near and far source earthquakes in past. The intensity of 1964 Calcutta earthquake was VII and 1897 Assam earthquake was VIII in MMI scale. The city have suffered many distance earthquake like 1918 Srimangal Earthquake, 1930 Dubhri Earthquake, 1934 Bihar Nepal Earthquake, 2011 Sikkim Earthquake (Shiuly & Narayan, 2012; Mohanty & Walling, 2008, Jhingram et al., 1969; GSI, 2000). The unexpected shaking has raised a serious question about the safety of Kolkata during earthquake and needs seismic microzonation.
Seismic microzonation of Delhi was carried out by Mukhopadhyay et al. (2002) by H/V ratio method. Anbazhagan and Sitharam (2007) conducted seismic hazard analysis for Bangalore City using deterministic and probabilistic approach and also developed peak ground acceleration map and hazard curves. They developed 3-D subsurface modeling of the geotechnical data using SPT test and borehole information. Measurement of shear wave velocity and evaluation of dynamic properties of soil in Bangalore was done using multi channel analysis of surface wave (MASW). Site amplification was computed by both by MASW result and one dimensional wave propagation technique SHAKE 2000. Site specific analysis for a seismically vulnerable site near Ahmedabad, Gujarat was evaluated out by Boominathan and Krishna Kumar (2010). In this study the seismic hazard analysis was carried out by DSHA approach and the ground response analysis was carried out by equivalent linear approach using SHAKE2000. Peak Ground Acceleration (PGA) and response spectra considering the local site effects of Bangalore city was evaluated by Sitharam and Vipin (2010). Shear wave velocity investigation for ten representative sites of national capital territory, New Delhi was carried out by Mahajan et al. (2011). A new site classification for India, China and Australia based on average soil thickness, shear wave velocity up to engineering bedrock was proposed by Anbazhagan and Sheikh (2012). Seismic ground response analysis of some typical sites of Guwahati City using one dimensional equivalent–linear ground response analyses were performed by Kumar and Murali Krishna (2013).