Revised Probabilistic Seismic Hazard Mapping for Greater Tehran Based on Updated Tectonic Interpretations

Iran ranks among the world's most seismically active regions, and its capital, Tehran, has endured major earthquakes throughout both prehistoric and documented history. Accurately characterizing ground motion parameters in this region is therefore critical for both public safety and informed urban development. In recent decades, paleoseismological investigations of Tehran's surrounding faults have provided crucial insights into prehistoric seismicity and long-term fault slip behavior. Despite their importance, these findings have been largely overlooked in previous hazard models. This study presents a probabilistic seismic hazard assessment (PSHA) for the Tehran metropolitan area that integrates updated tectonic interpretations and contemporary seismotectonic datasets. Non-seismogenic features previously misclassified as active faults – such as the North Rey, South Rey, Kahrizak, and Eshtehard scarps – have been excluded following comprehensive geological and geomorphic re-evaluations. The revised model reflects a more realistic seismic hazard scenario. A logic-tree framework was implemented using both qualitative and quantitative seismicity data, combined with NGA-West2 ground motion prediction equations (GMPEs), to produce high-resolution spectral acceleration maps for return periods of 475, 975, and 2475 years. Results indicate that several areas – particularly southeastern Tehran – exhibit significantly lower ground motion levels than previously estimated, emphasizing the need to update seismic design criteria for these zones. The resulting hazard model – scientifically validated and aligned with contemporary site-specific PSHA advances – provides a robust foundation for seismic risk mitigation and code development in Tehran and other seismically threatened urban regions worldwide.