Vulnerable Cores, Expanding Peripheries: Intra-Urban Population Redistribution and Seismic-Risk Exposure Across Istanbul’s 847 Mahalle, 2007–2035

This paper develops a scenario-based population modelling framework for the 847 mahalle (smallest administrative unit) of Istanbul, Türkiye, extending an empirical baseline for 2007–2025 into prospective scenarios to 2035. The baseline combines rank-size (Zipf) analysis, density quintile trajectories, trajectory classification, and phase-diagram analysis of early versus late-period growth. It reveals a persistent U-shaped deviation from the Zipf benchmark: both the most and least populous mahalle grew strongly through suburban mega-development and peri-urban expansion, respectively, while the established inner-city middle tier remained essentially unchanged. Density followed an inverted gradient, rising sharply on the low-density suburban fringe and contracting in the hyper-dense core. Building on this baseline, the paper defines a baseline continuation (S0) and four alternative scenarios: moderate economic stress (S1), a major North Anatolian Fault earthquake (S2), a combined shock (S3), and policy-led urban renewal (S4). The baseline trajectory amplifies existing inequalities; seismic and economic shocks compress upper-tail growth while generating displacement demand in outer-ring mahalle; and only S4 partially reverses the density-gradient inversion, by stimulating inner-city regeneration under Türkiye’s risky-area programme. The findings link intra-urban population redistribution to seismic-risk exposure and inform spatially targeted planning.