Evaluation of Seismic Demand and Structural Damage Caused by the Mw 6.2 Silivri (İstanbul) Earthquake (April 23, 2025)

This study investigates the seismic demands of the 23 April 2025 Silivri earthquake (M _w = 6.2) and damage distribution across 38,049 inspected buildings in İstanbul. Although the building stock is characterized by poor structural quality, no significant damage was reported, even at settlements with a PGA of 0.21g. Post-earthquake damage assessments were compared with pre-estimated seismic risk distributions, providing a rare opportunity to evaluate predictive models against real outcomes. A critical discussion of the soil amplification factors prescribed in the 2018 Turkish Seismic Design Code is conducted using the recorded ground-motion amplitudes from approximately one million buildings. The performance of the substandard building stock in İstanbul is further evaluated by integrating observed damage distributions with structural characteristics and pre-earthquake seismic risk estimations for nearly 25,000 reinforced concrete buildings. A strong agreement is observed between pre-earthquake risk levels and post-earthquake damage observations, revealing neighborhood-scale damage hotspots and providing validation for large-scale seismic risk assessments. Comparative analyses demonstrate that earthquakes with significantly higher PGA values may not necessarily result in widespread damage, highlighting the importance of spectral demand measures and ground-motion duration. The detailed numerical analyses of a representative substandard building that survived the earthquake undamaged help to explain why many structurally deficient buildings in İstanbul sustained either no damage or only slight damage during this event. The results indicate that non-structural infill walls limited damage to the substandard building stock during the short-duration Silivri earthquake, whereas the buildings would have collapsed under a longer-duration record with similar PGA from another earthquake.