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J Seismol (2013) 17:593605 DOI 10.1007/s10950-012-9340-5
ORIGINAL ARTICLE
Ground motion estimation in Delhi from postulated regional and local earthquakes
Himanshu Mittal & Ashok Kumar & Kamal
Received: 25 July 2011 /Accepted: 17 October 2012 /Published online: 30 October 2012 # Springer Science+Business Media Dordrecht 2012
Abstract Ground motions are estimated at 55 sites in Delhi, the capital of India from four postulated earthquakes (three regional Mw07.5, 8.0, and 8.5 and one local). The procedure consists of (1) synthesis of ground motion at a hard reference site (NDI) and (2) estimation of ground motion at other sites in the city via known transfer functions and application of the random vibration theory. This work provides a more extensive coverage than earlier studies (e.g., Singh et al., Bull Seism Soc Am 92:555569, 2002; Bansal et al., J Seismol 13:89105, 2009). The Indian code response spectra corresponding to Delhi (zone IV) are found to be conservative at hard soil sites for all postulated earthquakes but found to be deficient for Mw08.0 and 8.5 earthquakes at soft soil sites. Spectral acceleration maps at four different natural periods are strongly influenced by the shallow geological and soil conditions. Three pockets of high acceleration values
are seen. These pockets seem to coincide with the contacts of (a) Aravalli quartzite and recent Yamuna alluvium (towards the East), (b) Aravalli quartzite and older quaternary alluvium (towards the South), and (c) older quaternary alluvium and recent Yamuna alluvium (towards the North).
Keywords Delhi . EGF. Himalayas . Response spectra . RVT
1 Introduction
India has a long history of earthquakes. In the last 50 years, the population of India has doubled and resulted in very rapid growth of settlements, especially in urban areas. Presently about 50 million people in India, living in the Himalayan region and adjoining plains, are at risk from earthquakes. During the last 200 years, the Indian peninsula has experienced several great earthquakes, namely: Kutch, Gujrat (1819), M08.0; Assam earthquake (1897), M08.7; Kangra earthquake (1905), M08.0; Bihar-Nepal earthquake (1934), M08.3; and Assam earthquake (1950), M08.5. Most of the Himalayas comprising North India and North eastern India are mapped as either seismic zone IV or V in the seismic zonation map of India (on a scale of II to V). Two of the...