Urban-Scale Geographic Deaggregation of Seismic Hazard in Tehran Using Probabilistic Modeling

Tehran is a seismically active megacity with a complex network of faults. While conventional deaggregation methods provide statistical insight, they lack spatial resolution regarding the contribution of seismic sources. In this study, standard Mw–R–ε deaggregation was performed using EZ-FRISK at three representative sites across northern, central, and southern Tehran. We then developed customized coded spatial logic algorithms to generate geographic deaggregation maps for peak ground acceleration (PGA) and spectral acceleration (SA) at each structure's fundamental period. The results reveal that the northern site (Saman Bank Tower) is predominantly influenced by near-field sources, notably the North Tehran and Mosha faults, while the southern site (Kashani Hospital) is mainly affected by high-magnitude, moderate-to-far field events. Site-to-site variation in source contributions reflects differences in fault proximity, soil conditions, and structural periods. Our approach enables spatially resolved hazard characterization, offering a robust foundation for seismic design, retrofitting prioritization, and building code development in urban-scale seismic risk assessment. These findings support targeted retrofitting and zoning policies for fault-dense megacities such as Tehran.