Journal of Earthquake Engineering, 14:898–917, 2010 Copyright Ó A.S. Elnashai & N.N. Ambraseys ISSN: 1363-2469 print / 1559-808X online DOI: 10.1080/13632461003653337 Synthesizing Broadband Time-Histories at Near Source Sites; Case Study, 2003 Bam Mw6.5 Earthquake AHMAD NICKNAM, REZA ABBASNIA, MOHSEN BOZORGNASAB, and YASSER ESLAMIAN Civil Engineering Department, Iran University of Science and Technology, Tehran, Iran The main objective of this article is to synthesize the 2003 Bam earthquake. A hybrid method is proposed for synthesizing the near-fault broadband timehistories; a theoretical green’s function method and a stochastic finite-fault approach for generating time histories at low and high frequencies, respectively. A genetic algorithm is developed to optimize the differences between synthesized and recorded ground motions. The proposed technique can be used for dynamic nonlinear analysis of structures and site specific hazard analysis of the regions with lack of sufficient data and also for retrofitting the damaged structures during Bam earthquake, particularly the well-known adobe buildings of Arg-e-Bam. Keywords Hybrid Method; Bam Earthquake; Broadband Time History; Genetic Algorithm; Near Source; Velocity Pulse 1. Introduction Within the last ten years, many Iranian cities, such as Bam, Zarand, and Karaj, have had a tremendous growth of urban areas in seismically active regions. Only recently, the seismologists have begun to realize how the shaking within several kilometers of a fault differs from shaking farther away and how this affects the seismic risk [Aagaard et al., 2001]. Today, it is quite postulated that near-source ground motions containing large displacement and velocity pulses could potentially cause great harm to modern flexible buildings [Heaton et al., 1995; Hall et al., 1995; Hall, 1998]. Due to specific characteristics of near source ground motions, structural damages are only apparent in moderate to large earthquakes, and irregular occurrence of such earthquakes makes the task of understanding near-source ground motions difficult. The main motivation of this study is the 2003 Bam earthquake which caused too much loss of lives. In this article, we present a technique for modeling ground shaking which includes near source problems, directivity effects to be used in performance evaluation of important structure in region under study. 1.1. Strong Motion Synthesis Techniques The discrete wave number method, originally introduced by Bouchon and Aki [1977], is used for simulation process of low-frequency parts of the earthquake. The high-frequency Received 30 October 2009; accepted 26 January 2010. Address correspondence to Ahmad Nicknam, Civil Engineering Department, Iran University of Science and Technology, Tehran, Iran; E-mail: a_nicknam@iust.ac.ir 898