Site-specific ground response analysis

Abstract

The local soil conditions have a profound influence on ground response during earthquakes. The recent destructive earthquakes have again demonstrated that the topography, nature of the bedrock and nature and geometry of the depositional soils are the primary factors thatinfluence local modifications to the underlying motion. We highlight the engineering importance of site-specific ground response analysis and difficulties faced in conducting a complete ground response analysis. Steps to be followed in conducting a meaningful site amplification study are explained. Difficulties/uncertainties in choosing an input ground motion are discussed and the various methods currently available for site amplification study are summarized. A casestudy on ground response analysis of a site in Ahmedabad City during the Bhuj earthquake is presented. The study shows that the varying degree of damage to multistorey buildings in the close proximity of Sabarmati river area in Ahmedabad was essentially due to amplification of the ground. Amplification was attributed to the fact that the natural frequencies of the building and frequency content of the ground motion recorded on the ground floor of the Regional Passport StaffQuarters building are in close proximity.