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چکیده
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The assessment and modeling of earthquake forces and their influence on structural performance remain persistent challenges in seismic engineering, particularly in regions characterized by complex tectonics and enclosed fault systems. In Iraq, as in many seismically active regions, conventional design methodologies have primarily relied on Uniform Hazard Ground Motions (UHGM) derived from probabilistic seismic hazard analysis (PSHA). These motions are uniformly applied to all structures, irrespective of their dynamic response characteristics, which results in inconsistent probabilities of collapse despite nominally uniform hazard levels. Addressing this limitation, recent international seismic provisions, such as ASCE 7-22, have advanced the concept of risk-targeted design. This approach integrates probabilistic hazard modeling with structural performance assessment to achieve more consistent and reliable collapse probabilities across various building categories. This research develops the first comprehensive Risk-Targeted Ground Motion (RTGM) maps for Iraq, explicitly incorporating regional seismicity, active fault systems, and the tectonic framework, with particular emphasis on the Zagros fold–thrust belt. Spectral accelerations corresponding to key vibration periods, including PGA, Sa (0.2s), and Sa (1.0s), were evaluated within the Maximum Considered Earthquake (MCE) framework. The analysis also accounts for structural uncertainties by introducing the β factor, which captures variability in structural capacity and collapse resistance. RTGM values were calculated to correspond to a uniform 1% probability of collapse in 50 years, thereby providing a consistent safety margin for ordinary, essential, and critical structures. The findings reveal pronounced spatial variability in seismic hazard across Iraq. Northern and northeastern regions, particularly those adjacent to the Zagros fault system, exhibit the highest RTGM values, reflecting elevated seismic risk, whereas central and southern regions demonstrate moderate to low hazard levels. Sensitivity analyses indicate that increases in β substantially amplify spectral accelerations, especially for short-period structures, underscoring the importance of incorporating epistemic and aleatory uncertainties in risk-targeted seismic design. Comparisons with traditional UHGM confirm that RTGM maps provide more accurate and performance-consistent representations of seismic demand, thereby reducing the risks of both overdesign and underdesign. The RTGM maps produced through this research establish a scientifically rigorous foundation for the revision and modernization of Iraqi seismic codes. They promote the adoption of performance-based design methodologies aligned with international risk-targeted standards, ultimately enhancing structural resilience, safeguarding human life, and reducing seismic risk for infrastructure across Iraq’s earthquake-prone regions.
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