ORIGINAL PAPER Nonlinear Analysis of Local Site Effects on Seismic Ground Response in the Bam Earthquake M. H. T. Rayhani Æ M. H. El Naggar Æ S. H. Tabatabaei Received: 14 September 2006 / Accepted: 22 August 2007 Ó Springer Science+Business Media B.V. 2007 Abstract The influence of local geologic and soil conditions on the intensity of ground shaking is addressed in this study. The amplification of the ground motion due to local site effects resulted in severe damage to dwellings in the Bam area during the 2003 Bam Earthquake. A unique set of strong motion acceleration recordings was obtained at the Bam accelerograph station. Although the highest peak ground acceleration recorded was the vertical component (nearly 1 g), the longitudinal component (fault-parallel motion) clearly had the largest maximum velocity as well as maximum ground displacement. Subsurface geotechnical and geophys- ical (down-hole) data in two different sites have been obtained and used to estimate the local site condition on earthquake ground motion in the area. The ground response analyses have been conducted considering the nonlinear behavior of the soil deposits using both equivalent linear and nonlinear approaches. The fully nonlinear method embodied in FLAC was used to evaluate the nonlinear soil properties on earthquake wave propagation through the soil layer, and com- pare with the response from the equivalent linear approach. It is shown that thick alluvium deposits amplified the ground motion and resulted in signif- icant damage in residential buildings in the earthquake stricken region. The comparison of results indicated similar response spectra of the motions for both equivalent and nonlinear analyses, showing peaks in the period range of 0.3–1.5 s. However, the amplification levels of nonlinear analysis were less than the equivalent linear method especially in long periods. The observed response spectra are shown to be above the NEHRP building code design requirements, especially at high frequencies. Keywords Ground response  Bam earthquake  Site effect  Nonlinear 1 Introduction The powerful earthquake of December 26, 2003 almost destroyed the city of Bam that is located in the southeastern part of Iran. The magnitude of the earthquake was M w 6.6 (USGS), its epicenter was close to City of Bam in Kerman province, and the focal depth was estimated to be 8–10 km. The city had a population of around 150,000 prior to the earthquake. The earthquake destroyed almost 70% of M. H. T. Rayhani (&)  M. H. El Naggar Department of Civil and Environmental Engineering, University of Western Ontario, London, ON, Canada N6A 5B9 e-mail: mrayhani@ce.queensu.ca; mtofighr@uwo.ca M. H. El Naggar e-mail: helnaggar@eng.uwo.ca S. H. Tabatabaei Geotechnical Department, Building and Housing Research Center, P.O. Box 13145-1696, Tehran, Iran e-mail: htabatabaei@bhrc.ac.ir 123 Geotech Geol Eng DOI 10.1007/s10706-007-9149-0