Throughout history, human societies have been exposed to destructive natural hazards and have continuously sought effective measures to reduce their impacts. Among these hazards, earthquakes are considered one of the most destructive events in urban areas, causing not only human casualties but also extensive damage to buildings, urban infrastructure, public service facilities, and critical lifeline systems. This study aims to assess the potential human and economic losses resulting from a design-level earthquake in District 9 of Karaj Metropolis, Iran. The study area is characterized by high seismic hazard, diverse building stock, different construction periods, and proximity to active faults, making it highly vulnerable to earthquake damage. The assessment was conducted using the SELENA software package based on the HAZUS methodology within a Geographic Information System (GIS) environment. Data on building type, occupancy, number of stories, construction year, structural system, soil conditions, and neighborhood population were collected and subsequently refined through field surveys. Buildings were classified according to construction age and construction quality, while seismic damage was estimated using capacity curves and seismic design levels. The results indicate that District 9 is highly vulnerable to the selected design earthquake. Considerable human and economic losses are expected throughout the study area. The highest percentage of injured people is predicted to occur at 10:00 a.m., corresponding to the daytime population distribution considered in the analysis. Furthermore, one neighborhood is estimated to experience an economic loss of approximately 16%. These findings highlight the importance of incorporating seismic loss assessment into urban planning and disaster risk management. The results can serve as an effective tool for reducing seismic risk, improving disaster management, and supporting decision-making during the preparedness, response, and post-earthquake recovery phases.